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PubMed1996

Comparing mass spectrometric characteristics of peptides and peptoids.

The collision-induced dissociation (CID) spectra of the [M+H]+ ions of a pentapeptide and the corresponding peptoid and retropeptoid have been compared. The spectra of the peptide and peptoid both exhibit B- and Y"-type sequence ions at identical m/z values. In contrast to the peptide, the [M+H]+ ion of the peptoid and all sequence ions containing an N-substituted glycine derivative corresponding to a tyrosine amino acid residue can easily lose a C7H6O molecule in a charge-remote fragmentation process. The presence of N-substituted glycine residues in a peptoid is further apparent from the presence of N-substituted immonium ions, which differ significantly in their fragmentation behaviour from the corresponding immonium ions observed in the spectra of common oligopeptides. Loss of the CH2 = NH imine molecule is the dominant fragmentation reaction in the CID spectra of all peptoid immonium ions investigated in this study. The elimination of the CH = NH2 ylide analogue from common peptide immonium ions is energetically less favourable as shown by ab initio calculations. The relative heat of formation of the CH = NH2 ylide neutral appeared to be 168 kJ mol-1 more than that of the CH2 = NH imine molecule.

Amino Acid Sequence↗
PubMed1998

Structure activity relationship of homochiral 7-substituted 1-aminoindans as 5-HT1A receptor ligands.

A series of homochiral 7-substituted 1-aminoindans was prepared by means of asymmetric reductive amination from racemic 7-substituted 1-indanones via E-imines and E-imine/enamine mixtures, respectively, and subjected to 5-hydroxytryptamine (5-HT) receptor subtype binding studies. The ee's of the title compounds were determined by HPLC of the corresponding Mosher's amides and range from 96 to 99.9%. The absolute configuration was elucidated by means of correlation CD spectroscopy. On the basis of the pK1 values obtained from various test systems, structure activity relationships have been established with respect to the absolute configuration, degree of N-alkylation, and the type of 7-substituents. The tested 1-aminoindans show the highest affinity to the 5-HT1A receptor, with decreasing magnitude for the 5-HT2A, 5-HT1D, and 5-HT2C receptors. The highest affinities for the 5-HT1A receptor were observed for the R-(-)-7-propoxy-1-(di-n-propylamino)indan hydrochloride (R-(-)-30). S,S'-(+)-7-benzylamido-1-(1-phenylethylamino)indan hydrochloride [S,S'-(+)-19] and R-(-)-7-methoxy-1-(di-n-propylamino)indan hydrogenembonate (R-(-)-29) with pK1 = 7.07 +/- 0.19, 6.40 +/- 0.09, and 6.22 +/- 0.10, respectively, in comparison to 8-OH-DPAT with pK1 = 8.70 +/- 0.30. Nearly all other compounds showed low affinity at all 5-HT receptors tested. The three above mentioned ligands were tested on HeLa cells (cell line HA6) expressing recombinant human 5-HT1A receptors for their effects on forskolin-stimulated cAMP accumulation in intact cells. Both the di-n-propylamino substituent bearing R-(-)-30 and R-(-)-29 acted as efficacious agonists with a pEC50 value of 5.89 +/- 0.20 for R-(-)-30 compared to 5-HT with a pEC50 value of 8.06 +/- 0.14, S,S'-(+)-19 with the 1-phenylethylamino substituent was devoid of intrinsic activity up to the highest tested concentration (10 microM).

Colforsin↗
PubMed2002

Transfer hydrogenation processes to mu(3)-alkylidyne groups on the organotitanium oxide [Ti(3)Cp*O(3)].

The photochemical treatment of mu(3)-alkylidyne complexes [[TiCp*(mu-O)](3)(mu(3)-CR)] (R=H (1), Me (2), Cp*=eta(5)-C(5)Me(5)) with the amines (2,6-Me(2)C(6)H(3))NH(2), Et(2)NH, and Ph(2)NH and the imine Ph(2)C=NH leads to the partial hydrogenation of the alkylidyne moiety that is supported on the organometallic oxide, [Ti(3)Cp*O(3)], and the formation of new oxoderivatives [[TiCp*(3)(mu-CHR)(R'NR")] (R"=2,6-Me(2)C(6)H(3), R'=H, R=H (3), Me (4); R'=R"=Et, R=H (5), Me (6); R'=R"=Ph, R=H (7), Me (8)) and [[TiCp*(mu-O)](3)(mu-CHR)(N=CPh(2))] (R=H (9), R=Me (10)), respectively. A sequential transfer hydrogenation process occurs when complex 1 is treated with tBuNH(2), which initially gives the mu-methylene [[TiCp*(mu-O)](3)(mu-CH(2))(HNtBu)] (11) complex and finally, the alkyl derivative [[TiCp*(mu-O)](3)(mu-NtBu)Me] (12). Furthermore, irradiation of solutions of the mu(3)-alkylidyne complexes 1 or 2 in the presence of diamines o-C(6)H(4)(NH(2))(2) and H(2)NCH(2)CH(2)NH(2) (en) affords [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(6)H(4)NH)] (13) and [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(2)H(4)NH)] (14) by either methane or ethane elimination, respectively. In the reaction of 1 with en, an intermediate complex [[TiCp*(mu-O)](3)(mu-CH(2))(NHCH(2)CH(2)NH(2))] (15) is detected by (1)H NMR spectroscopy. Thermal treatment of the complexes 4-10 quantitatively regenerates the starting mu(3)-alkylidyne compounds and the amine R'(2)NH or the imine Ph(2)C=NH; however, heating of solutions of 3 or 4 in [D(6)]benzene or a equimolecular mixture of both at 170 degrees C produces methane, ethane, or both, and the complex [[TiCp*(mu-O)](3)[mu(3)-eta(2)-NC(6)H(3)(Me)CH(2)]] (16). The molecular structure of 8 has been established by single-crystal X-ray analysis.

Journal Article↗
PubMed2002

Oligomerization and hydroamination of terminal alkynes promoted by the cationic organoactinide compound [(Et2N)3U][BPh4].

The three ancillary amido moieties in the cationic complex [(Et2N)3U][BPh4] are highly reactive and are easily replaced when the complex is treated with primary amines. The reaction of [(Et2N)3U][BPh4] with excess tBuNH2 allows the formation of the cationic complex [(tBuNH2)3(tBuNH)3U][BPh4]. X-ray diffraction studies on the complex indicate that three amido and three amine ligands are arranged around the cationic metal center in a slightly distorted octahedral mer geometry. The cationic complex reacts with primary alkynes in the presence of external primary amines to primarily afford the unexpected cis dimer and, in some cases, the hydroamination products are obtained concomitantly. The formation of the cis dimer is the result of an envelope isomerization through a metal-cyclopropyl cationic complex. In the reaction of the bulkier alkyne tBuC identical to CH with the cationic uranium complex in the presence of various primary amines, the cis dimer, one trimer, and one tetramer are obtained regioselectively, as confirmed by deuterium labeling experiments. The trimer and the tetramer correspond to consecutive insertions of an alkyne molecule into the vinylic CH bond trans to the bulky tert-butyl group. The reaction of (TMS) C identical to CH with the uranium catalyst in the presence of EtNH2 followed a different course and produced the gem dimer along with the hydroamination imine as the major product. However, when other bulkier amines were used (iPrNH2 or tBuNH2) both hydroamination isomeric imines Z and E were obtained. During the catalytic reaction, the E (kinetic) isomer is transformed into the most stable Z (thermodynamic) isomer. The unique reactivity of the alkyne (TMS) C identical to CH with the secondary amine Et2NH is remarkable because it afforded the trans dimer and the corresponding hydroamination enamine. The latter probably results from the insertion of the alkyne into a secondary metal-amide bond, followed by protonolysis.

Journal Article↗
PubMed2004

Schiff base of gossypol with 3,6,9-trioxa-decylamine complexes with monovalent cations studied by mass spectrometry, (1)H-NMR, FTIR, and PM5 semiempirical methods.

A new Schiff base of gossypol with 3,6,9-trioxo-decylamine (GSTB) forms stable complexes with monovalent cations. This process of complex formation was studied by electrospray ionization mass spectrometry, (1)H-NMR and FTIR spectroscopy, and the PM5 (parametric method 5) semiempirical method. It is found that GSTB forms 1 : 1 and 1 : 2 complexes with Li(+) and Na(+) and 1 : 1 complexes with K(+), Rb(+), or Cs(+) cations and exists in all these complexes in the enamine-enamine tautomeric form. Moreover, within these complexes only Li(+) cations can fluctuate between the oxygen atoms of trioxo-alkyl chains. All other cations are strongly localized. In the complex of GSTB with two protons localized on the N atoms of the Schiff base, the imine-imine tautomeric form is realized. The complexes of the Schiff base with K(+), Rb(+), or Cs(+) cations are the 1 : 1 type with the oxygen atoms of the trioxo-alkyl chains, as well as the O(1)H or O(1')H group coordinating the cation. The structures of the complexes are calculated by the PM5 semiempirical method and discussed.

Amines↗
PubMed2004

The schiff base of gossypol with 3,6,9,12,15,18,21,24-octaoxa-pentacosylamine complexes and monovalent cations studied by electrospray ionization-mass spectrometry, (1)H nuclear magnetic resonance, Fourier transform infrared, as well as PM5 semiempirical methods.

A Schiff base of gossypol with 3,6,9,12,15,18,21,24-octaoxa-pentacosylamine (GSOB) forms stable complexes with monovalent cations. This process of complex formation was studied by electrospray ionization-mass spectrometry, (1)H-NMR and Fourier transform infrared spectroscopy as well as by the PM5 semiempirical method. It was found that GSOB forms 1:6 complexes with Li(+) and Na(+), and 1:4 complexes with K(+) as well as 1:2 complexes with Rb(+) or Cs(+) cations and exists in all these complexes in the enamine-enamine tautomeric form. Moreover, within these complexes only Li(+) cations can fluctuate between the oxygen atoms of the octaoxaalkyl chains. The interactions of Li(+) cations with hydroxyl groups of the gossypol part is also possible. All other cations are much more localized. In the complex of GSOB with protons, a 1:2 stoichiometry is realized. The two protons are localized on the N atoms of the Schiff base, and the complex exists in the imine-imine tautomeric form. The structures of the complexes are calculated by PM5 semiempirical methods and discussed.

Cations, Monovalent↗
PubMed2006

1H- and 13C-NMR, FTIR, UV-VIS, ESI-MS, and PM5 studies as well as emission properties of a new Schiff base of gossypol with 5-methoxytryptamine and a new hydrazone of gossypol with dansylhydrazine.

A new Schiff base of gossypol with 5-methoxytryptamine (GSTR) and a new hydrazone of gossypol with dansylhydrazine (GHDH) have been synthesized and studied by Fourier transform infrared (FTIR), 1H and 13C nuclear magnetic resonance (NMR), ultraviolet-visible (UV-VIS), electrospray ionization-mass spectroscopy (ESI-MS) as well as the parametric method PM5. The spectroscopic methods have provided clear evidence that GSTR exists in chloroform solution as an enamine-enamine tautomer, whereas GHDH is present in chloroform as a N-imine-N-imine tautomer. The fluorescence spectra of both compounds indicate that their quantum yield of fluorescence is increased by one or two orders of magnitude compared to that of pure gossypol. The ESI-MS spectra of the 1:1 mixtures of GSTR or GHDH with formic acid have demonstrated that both compounds exist as protonated monomers in the gas phase, whereas GHDH can also exist in a stable protonated dimeric structure. The structures of the stable tautomers are calculated and visualized using the PM5 semiempirical method. The intra- and intermolecular hydrogen bonds within these structures are discussed.

5-Methoxytryptamine↗
PubMed2006

Multinuclear magnetic resonance, electrospray ionization-mass spectroscopy, and parametric method 5 studies of a new derivative of gossypol with 2-thiophenecarbohydrazide as well as its complexes with LI+, Na+, K+, RB+, and Cs+ cations.

A new derivative of racemic gossypol with 2-thiophenecarbohydrazide (GHHT) and its complexes with monovalent cations have been synthesized and studied by electrospray ionization-mass spectroscopy (ESI-MS), multinuclear nuclear magnetic resonance (NMR), as well as by the Parametric Method 5 (PM5) methods. It is demonstrated that GHHT forms stable complexes of 1:1 stoichiometry with monovalent metal cations. The structures of the complexes are stabilized by three types of intramolecular hydrogen bonds. The spectroscopic methods have provided clear evidence that GHHT and its complexes exist in the DMSO-d6 solution in the N-imine-N-imine tautomeric forms. The structures of the GHHT and its complexes with Li+, Na+, K+, Rb+, and Cs+ cations are visualized and discussed in detail.

Cations, Monovalent↗
PubMed2003

One-step preparation, structural assignment, and X-ray study of 2,2-di-n-butyl- and 2,2-diphenyl-6-aza-1,3-dioxa-2-stannabenzocyclononen-4-ones derived from amino acids.

Twenty-four 2,2-di-n-butyl- and 2,2-diphenyl-6-aza-1,3-dioxa-2-stannabenzocyclononen-4-ones, each having a transannular N-->Sn bond, have been prepared by one-step reactions of alpha-amino acids (1 a-l), salicylaldehyde (2), and either di-n-butyltin(IV) oxide (3) or diphenyltin(IV) oxide (4). The new methodology constitutes an easy, highly efficient one-step synthesis of diorganotin(IV) derivatives, such as 5 a-l and 6 a-l, from iminic tridentate ligands without isolation of the Schiff bases. The structures of all the compounds have been established by a combination of (1)H, (13)C, (15)N, and (119)Sn NMR spectroscopy, IR spectroscopy, mass spectrometry, and elemental analysis. In all cases, the (119)Sn chemical shifts, as well as the (1)J((119)Sn,(13)C) coupling constants, are indicative of pentacoordinated tin atoms in solution. The structures of compounds 5 a, d, f, 6 a, b, b-racemic, c, d, f, g, and l have been established by single-crystal X-ray diffraction analyses. The tin atoms in 5 d, f, 6 a, b, b-racemic, c, d, g, and l each have a distorted trigonal-bipyramidal (TBP) geometry, with the oxygen atoms from the phenol and carboxylate moieties occupying the axial positions, and the imine nitrogen and phenyl or n-butyl substituents occupying the equatorial positions. Compounds 5 a and 6 f show distorted octahedral (DOC) geometries due to intermolecular coordination of the carbonyl oxygen to the tin atom, in a trans disposition to the N-->Sn bond, leading to trimeric 5 a and a polymeric structure for compound 6 f. Additionally, measurement of the one-bond coupling constants (1)J((119)Sn,(13)C) in diphenyltin(IV) complexes (6 a-l) and their correlation with the CSn-C bond angles has allowed the derivation of an equation that can be applied to assess the geometry around the tin atom for other diphenyltin(IV) compounds in solution.

Amino Acids↗
PubMed2004

Enantioselective total syntheses of the Ipecacuanha alkaloid emetine, the Alangium alkaloid tubulosine and a novel benzoquinolizidine alkaloid by using a domino process.

The first enantioselective syntheses of the Ipecacuanha alkaloid emetine (1) and the Alangium alkaloid tubulosine (2) is described employing a domino Knoevenagel/hetero-Diels-Alder reaction and an enantioselective catalytic transfer hydrogenation of imines as key steps. Thus, hydrogenation of the imine 15 with the catalyst (R,R)-16 gives the tetrahydroisoquinoline 14 with 95 % ee which was transformed into the aldehyde (1S)-7. The three-component domino reaction of (1S)-7 with 6 and 8 led to 19, which in a second domino process was treated with K(2)CO(3) in methanol followed by a hydrogenation to give the benzoquinolizidine 4 together with the diastereomers 22 and 23 in a overall yield of 66 %. Further transformation of 4 with the amines 3 and 5 yielded enantiopure emetine (1) and tubulosine (2), respectively. In addition, starting from 19 the novel benzoquinolizidine alkaloid 34 was synthesised; this compound resembles the vallesiachotamine alkaloid dihydroantirhin 31, which has not been isolated so far but probably must also exist in nature.

Alangiaceae↗
PubMed2003

Instantaneous SmI2/H2O/amine-mediated reductions in THF.

The SmI(2)-mediated reductions of ketones, imines, and alpha,beta-unsaturated esters have been shown to be instantaneous in the presence of H(2)O and an amine in THF. The SmI(2)-mediated reductions are not only shown to be fast and quantitative by the addition of H(2)O and an amine, but the workup procedures are also simplified. Competing experiments with SmI(2)/H(2)O/amine confirmed that alpha,beta-unsaturated esters could be selectively reduced in the presence of ketones or imines. Comparison of analogue ligands showed that nitrogen and phosphorus ligands are superior to oxygen and sulfur ligands in these reductions. The trialkylphosphine 1,2-bis(dimethylphosphino)ethane (DMPE) provided a primary kinetic isotope effect, yielding a k(H)/k(D) of 4.5.

Amines↗
PubMed2003

Formation, preservation, and cleavage of the disulfide bond by vanadium.

Reaction of the disulfide [HpicanS](2) (HpicanS is the carboxamide based on picolinate (pic) and o-mercaptoaniline (anS); the [] brackets are used to denote disulfides) with [VOCl(2)(thf)(2)] leads to reductive scission of the disulfide bond and formation of the mixed-valence (V(IV)/V(V)) complex anion [(OVpicanS)(2)mu-O](-) (1), with the dianionic ligand coordinating through the pyridine-N atom, the deprotonated amide-N atom, and thiophenolate-S atom. Reductive cleavage of the SbondS bond is also observed as [VCl(2)(tmeda)(2)] (tmeda=tetramethylethylenediamine) is treated with the disulfides [HsalanS](2) or [HvananS](2) (HsalanS and HvananS are the Schiff bases formed between o-mercaptoaniline and salicylaldehyde (Hsal) or vanillin (Hvan), respectively), yielding the V(III) complexes [VCl(tmeda)(salanS)] (2 a), or [VCl(tmeda)(vananS)] (2 b). The disulfide bond remains intact in the aerial reaction between [HsalanS](2) and [VCl(3)(thf)(3)] to yield the V(V) complex [VOCl[salanS](2)] (3), where (salanS)(2-) coordinates through the two phenolate and one of the imine functions. The S-S bond is also preserved as [VO(van)(2)] or [VO(nap)(2)] (Hnap=2-hydroxynaphthalene-1-carbaldehyde) is treated with bis(2-aminophenyl)disulfide, [anS](2), a reaction which is accompanied by condensation of the aldehyde and the diamine, and complexation of the resulting bis(Schiff bases) [HvananS](2) or [HnapanS](2) to form the complexes [VO[vananS](2)] (4 a) or [VO[napanS](2)] (4 b). In 4 a and 4 b, the phenolate and imine functions, and presumably also one of the disulfide-S atoms, coordinate to V(IV). 2-Mercaptophenyl-2'-pyridinecarboxamide (H(2)picanS) retains its identity in the presence of V(III); reaction between [VCl(3)(thf)(3)] and H(2)picanS yields [V[picanS](2)](-) (5). The dithiophenolate 2,6-bis(mercaptophenylthio)dimethylpyridine (6 a) is oxidized, mediated by VO(2+), to the bis(disulfide) octathiadiaza-cyclo-hexaeicosane 6 b. The relevance of these reactions for the speciation of vanadium under physiological conditions is addressed. [HNEt(3)]-1.0.5 NEt(3,) 3.3 CH(2)Cl(2), [HsalanS](2), [HNEt(3)]-5, and 6 b.4 THF have been characterized by X-ray diffraction analysis.

Crystallography, X-Ray↗
PubMed2004

Olefins as steering ligands for homogeneously catalyzed hydrogenations.

Iridium(I) complexes containing a (5H-dibenzo[a,d]cyclohepten-5-yl)-phosphane (tropp(R); R = phosphorus-bound substituent = Ph, Cyc) as a rigid, concave-shaped, mixed phosphane olefin ligand were prepared and tested as catalyst precursors in the hydrogenation of imines. With the complex [Ir(tropp(Cyc))(cod)]OTf, turnover frequencies (TOFs) of >6000 h(-1) were reached in the hydrogenation of N-phenyl-benzylidenamine, PhN==CHPh. Lower activities (TOF>80 h(-1)) are observed with N-phenyl-(1-phenylethylidene)amine, PhN==CMePh. Chiral tropp-type ligands were prepared in few simple steps. Monosubstitution of the olefinic unit in the dibenzo[a,d]cycloheptenyl moiety with (R)- or (S)-mentholate gave mixtures of diastereomers that could be separated and isolated in enantiomerically pure form. Iridium(I) complexes with these ligands are rare examples of side-on bonded enolether complexes. In catalytic imine hydrogenations, complete conversion (>98 %) was reached in all cases (conditions: p[H(2)] = 50 bar, T = 50 degrees C, t = 2 h, substrate/catalyst 100:1). The best enantiomeric excess (ee = 86 % S isomer) was reached with PhN==CMePh as substrate and the R,R form of the (10-menthyloxy-5H-dibenzo[a,d]cyclohepten-5-yl)diphenylphosphane ligand. The iridium(I) complex containing the same phosphane gave a 60 % ee (S isomer) with the enamide N-(1-phenylvinyl)acetamide as substrate (conditions: p[H(2)] = 4 bar, T = 50 degrees C, t = 18 h, substrate/catalyst = 50:1). These reactions constitute the first examples in which chiral olefins have been used as steering ligands in catalytic enantioselective hydrogenations.

Journal Article↗
PubMed2005

Template-directed synthesis of multiply mechanically interlocked molecules under thermodynamic control.

The template-directed construction of crown-ether-like macrocycles around secondary dialkylammonium ions (R2NH2+) has been utilized for the expedient (one-pot) and high-yielding synthesis of a diverse range of mechanically interlocked molecules. The clipping together of appropriately designed dialdehyde and diamine compounds around R2NH2+-containing dumbbell-shaped components proceeds through the formation, under thermodynamic control, of imine bonds. The reversible nature of this particular reaction confers the benefits of "error-checking" and "proof-reading", which one usually associates with supramolecular chemistry and strict self-assembly processes, upon these wholly molecular systems. Furthermore, these dynamic covalent syntheses exploit the efficient templating effects that the R2NH2+ ions exert on the macrocyclization of the matched dialdehyde and diamine fragments, resulting not only in rapid rates of reaction, but also affording near-quantitative conversion of starting materials into the desired interlocked products. Once assembled, these "dynamic" interlocked compounds can be "fixed" upon reduction of the reversible imine bonds (by using BH3.THF) to give kinetically stable species, a procedure that can be performed in the same reaction vessel as the inital thermodynamically controlled assembly. Isolation and purification of the mechanically interlocked products formed by using this protocol is relatively facile, as no column chromatography is required. Herein, we present the synthesis and characterization of 1) a [2]rotaxane, 2) a [3]rotaxane, 3) a branched [4]rotaxane, 4) a bis [2]rotaxane, and 5) a novel cyclic [4]rotaxane, demonstrating, in incrementally more complex systems, the efficacy of this one-pot strategy for the construction of interlocked molecules.

Journal Article↗
PubMed2006

Fine tuning of the oxidation locus, and electron transfer, in nickel complexes of pro-radical ligands.

A large number of complexes of the first-row transition metals with non-innocent ligands has been characterized in the last few years. The localization of the oxidation site in such complexes can lead to discrepancies when electrons can be removed either from the metal center (leading to an M((n+1)+) closed-shell ligand) or from the ligand (leading to an M(n+) open-shell ligand). The influence of the ligand field on the oxidation site in square-planar nickel complexes of redox-active ligands is explored herein. The tetradentate ligands employed herein incorporate two di-tert-butylphenolate (pro-phenoxyl) moieties and one orthophenylenediamine spacer. The links between the spacer and both phenolates are either two imines ([Ni(L1)]), two amidates ([Ni(L3)]2-), or one amidate and one imine ([Ni(L2)]-). The structure of each nickel(II) complex is presented. In the noncoordinating solvent CH2Cl2, the one-electron-oxidized forms are ligand-radical species with a contribution from a singly occupied d orbital of the nickel. In the presence of an exogenous ligand, such as pyridine, a Ni(III) closed-shell ligand form is favored: axial ligation, which stabilizes the trivalent nickel in its octahedral geometry, induces an electron transfer from the metal(II) center to the radical ligand. The affinity of pyridine for the phenoxylnickel(II) species is correlated to the N-donor ability of the linkers.

Crystallography, X-Ray↗
PubMed2007

Mechanistic study on rearrangement cascades starting from annulated 2-aza-hepta-2,4-dienyl-6-ynyl anions: formation of aniline and azepine derivatives.

Deprotonation of benzothiophene-derived alkynyl imine 11 with lithium diisopropylamide (LDA) and subsequent transmetalation with ZnCl2 etherate furnished azepine 12 upon aqueous workup. Similarly, alkynyl benzaldimine 1a gave a mixture of benzazepine 13 and naphthylamine 14. Allylic benzonitriles 15 a,b reacted to produce naphthylamine 16 upon deprotonation with LDA at room temperature. In an analogous manner, imino benzonitrile 17 may be converted into 4-amino isoquinoline 18 by means of an intramolecular nucleophilic attack on the nitrile function upon treatment with LDA. The allylic benzonitriles 19 a,b were prepared by LDA treatment of alkynyl imine 11. They were further converted to amino dibenzothiophene 20 by LDA deprotonation and aqueous workup. These various transformations represent the key steps of a multistep reaction cascade, which was previously postulated on the basis of quantum chemical calculations. Thus, all features of this complex rearrangement mechanism could now be confirmed experimentally. DFT calculations support the lower reactivity of zinc species in the ring-opening step compared to the lithium intermediates. All new compounds were completely characterized by spectroscopic data, including X-ray diffraction studies for the key compounds 12, 19 a, and 20.

Journal Article↗
PubMed1984

Preparation of 7,8-dimethoxy-3,4-dihydroisoquinoline, facile route to 7,8-dioxygenated-3,4-dihydroisoquinolines.

Oxidation of 7,8-dimethoxy-1,2,3,4-tetrahydroisoquinoline with potassium permanganate in acetone afforded 7,8-dimethoxy-3,4-dihydroisoquinoline as the primary product. Hence, oxidation of the appropriate secondary nonphenolic 7,8-dioxygenated tetrahydroisoquinoline alkaloid is thus a facile method for the generation of the corresponding imine. The imine is not easily prepared via the usual synthetic route involving ring closure of beta-phenethylamine derivatives.

Chemical Phenomena↗
PubMed1991

Isoxazoles. VII: Hydrolysis of 4-methyl-5-isoxazolylnaphthoquinone derivatives in aqueous solutions.

The kinetics for the degradation of 2-(4-methyl-5-isoxazolylamine)-N-(4-methyl-5-isoxazolyl)-1,4 -naphthoquinone-4- imine (1) in solution were investigated at 70 degrees C and at a constant ionic strength of 0.5 over a pH range of 1.75 to 12.85. The degradation rates were determined by absorption and second-derivative UV spectrometry. Two degradation products were identified in acidic and neutral pHs; they are 4-N-(4-methyl-5-isoxazolyl)-1,2-naphthoquinone (2) and 2-methyl-cyanoacetamide (5), respectively. In alkaline pH, two degradation products, 2-hydroxy-N-(4-methyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (3) and 5-amino-4-methylisoxazole (4), were isolated. The pathway for degradation of 1 in acidic and neutral pH followed consecutive first-order kinetics since 2 undergoes hydrolysis giving 2-hydroxy-1,4-napthoquinone (6) and 2-methylcyanoacetamide (5). No appreciable buffer effect on the degradation of 1 and 2 was observed for any of the buffer species in this study. The pH-rate profiles exhibited specific acid and specific basic catalysis for 1 and specific acid catalysis for 2. The maximum stability for 1 and 2 occurred in the neutral pH region.

Buffers↗