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PubMed1984

Stable free radical and benzoquinone imine metabolites of an acetaminophen analogue.

The enzymatic oxidation of the acetaminophen analogue 3',5'-dimethyl-4'-hydroxyacetanilide (3',5'-dimethylacetaminophen) with the horseradish peroxidase/hydrogen peroxide system forms a phenoxyl free radical metabolite. The structure of this free radical is established by a complete analysis of the ESR spectrum and confirmed by deuterium isotope substitution. Concomitant with phenoxyl radical formation, N-acetyl-3,5-dimethyl-p-benzoquinone imine was detected by optical spectroscopy. The free radical is also formed by comproportionation in solutions of the quinone imine containing added 3',5'-dimethylacetaminophen. In contrast to acetaminophen, the imine and radical metabolites are stable and can be detected without resort to rapid-mixing techniques. Factors leading to the increased stability of these metabolites relative to those formed from acetaminophen are discussed in terms of the toxicity of acetaminophen.

Acetaminophen↗
PubMed2000

Bis axial ligation of simple imine and methyleneamido groups by ruthenium porphyrins

Bis(N-ethylideneethanamine)ruthenium(ii) porphyrins, [Ru11(Por)(N(Et)=CHMe)2] (Por=TTP, 4-Cl-TPP), were prepared by the reaction of dioxoruthenium(VI) porphyrins with triethylamine in approximately 85% yields. The reaction between dioxoruthenium(VI) porphyrins and benzophenone imine afforded bis(diphenylmethyleneamido)ruthenium(IV) porphyrins, [Ru(IV)(Por)(N=CPh2)2] (Por=TTP, 3,4,5-MeO-TPP), in approximately 65% yields. These new classes of metalloporphyrins were characterized by 1H NMR, UV/Vis, and IR spectroscopy as well as by mass spectrometry and elemental analysis. The X-ray crystallographic structures of [Ru(II)(TTP)(N(Et)=CHMe)2] and [Ru(IV)(3,4,5-MeO-TPP)(N=CPh2)2] revealed an axial Ru-N bond length of 2.115(6) A for the imine complex and 1.896(8) A for the methyleneamido complex. Each of the N=CPh2 axial groups in [Ru(IV)(3,4,5-MeO-TPP)(N=CPh2)2] adopts a linear coordination mode with a corresponding Ru-N-C angle of 175.9(9)degrees. Spectral and structural studies revealed essentially single bonding character for the bis(imine) complexes but a multiple bonding character for the bis(methyleneamido) complexes with respect to their axial Ru-N bonds.

Journal Article↗
PubMed2004

Palladium-catalyzed cross-coupling reactions of amines with alkenyl bromides: a new method for the synthesis of enamines and imines.

The palladium-catalyzed cross-coupling reaction of alkenyl bromides with secondary and primary amines gives rise to enamines and imines, respectively. This new transformation expands the applicability of palladium-catalyzed C-N bond forming reactions (the Buchwald-Hartwig amination), which have mostly been applied to aryl halides. After screening of different ligands, bases, and solvents, the catalytic combination [Pd(2)(dba)(3)]/BINAP in the presence of NaOtBu in toluene gave the best results in the cross-coupling of secondary amines with 1-bromostyrene (dba=dibenzylideneacetone, BINAP=2,2'-bis(diphenylphosphino)-1,1'-binaphthyl). The corresponding enamines are obtained cleanly and in nearly quantitative yields. However, steric hindrance seems to be a limitation of the reaction, as amines carrying large substituents are not well converted. The same methodology can be applied to the coupling of secondary amines with 2-bromostyrene. Moreover, the reaction with substituted 2-bromopropenes allows regioselective synthesis of isomerizable terminal enamines without isomerization of the double bond. The best catalytic conditions for the cross-coupling of 1-bromostyrene with primary amines include again the use of the Pd(0)/BINAP/NaOtBu system. The reaction gives rise to the expected imines in very short times and with low catalyst loadings. A set of structurally diverse imines can be prepared by this methodology through variations in the structure of both coupling partners. However, 2-bromostyrene failed to give good results in this coupling reaction, probably due to product inhibition of the catalytic cycle. Competition experiments of vinyl versus aryl amination reveal that the reaction occurs preferentially on vinyl bromides.

Journal Article↗
PubMed2000

Imidacloprid, thiacloprid, and their imine derivatives up-regulate the alpha 4 beta 2 nicotinic acetylcholine receptor in M10 cells.

Neonicotinoids are the most important new class of insecticides of the last decade. They act as nicotinic acetylcholine receptor (AChR) agonists. This investigation tests the hypothesis for the first time that neonicotinoid insecticides and their imine derivatives up-regulate the alpha 4 beta 2 nicotinic AChR subtype, which represents >90% of the high-affinity [(3)H]nicotine binding sites in mammalian brain. The alpha 4 beta 2 receptor stably expressed in mouse fibroblast M10 cells was assayed after 3 days' exposure to the test compound, as [(3)H]nicotine binding following immunoisolation by monoclonal antibody (mAb 299) or as [(125)I]mAb 299 labeling for cell surface receptors. We found that imidacloprid (IMI) (one of the most important insecticides) and thiacloprid (THIA) increased [(3)H]nicotine binding levels (up-regulation of the alpha 4 beta 2 AChRs) by five- to eightfold with EC50s of approximately 70,000 and 19,000 nM, respectively, compared with 760 nM for (-)-nicotine. In contrast, two imine analogs [the desnitro metabolite of IMI (DNIMI) and the descyano derivative of THIA] gave up-regulation by eightfold and EC50s of 870 and 500 nM, respectively. The potency order for up-regulation by the five aforementioned compounds was correlated with their in vitro IC50s for inhibiting [(3)H]nicotine binding (r(2) = 0.99, n = 5), indicating that binding to the alpha 4 beta 2 receptor initiates the up-regulation. A potent olefin derivative of the THIA imine up-regulated with an EC50 of 22 nM. DNIMI-induced up-regulation mainly occurred intracellularly rather than at the cell surface. These findings in alpha 4 beta 2-expressing M10 cells indicate the possibility that some neonicotinoid insecticides or their metabolites, on accidental human exposure or when used for flea control on dogs, may also up-regulate the receptor in mammals.

Animals↗
PubMed2002

N-tert-butanesulfinyl imines: versatile intermediates for the asymmetric synthesis of amines.

N-tert-Butanesulfinyl aldimines 3 and ketimines 4 are exceedingly versatile intermediates for the asymmetric synthesis of amines. The N-tert-butanesulfinyl imines are prepared in high yields by condensing enantiomerically pure tert-butanesulfinamide 1, which is readily available in either configuration, with a wide range of aldehydes and ketones. The tert-butanesulfinyl group activates the imines for the addition of many different classes of nucleophiles, serves as a powerful chiral directing group, and after nucleophilic addition is readily cleaved by treatment of the product with acid. A wide range of highly enantioenriched amines, including alpha-branched and alpha,alpha-dibranched amines, alpha- and beta-amino acids, 1,2- and 1,3-amino alcohols, and alpha-trifluoromethyl amines, are efficiently synthesized using this methodology. In addition, N-tert-butanesulfinyl imine derivatives provide a new family of ligands for asymmetric catalysis.

Journal Article↗
PubMed2001

Tetranuclear mixed-metal M(II)2Cu(II)2 complexes derived from a phenol-based macrocyclic ligand having two N(amine)2O2 and two N(imine)2O2 metal-binding sites.

The reaction of N,N'-dimethyl-N,N'-ethylenebis(5-bromo-3-formyl-2-hydroxybenzylaminato)copper(II) with ethylenediamine in aqueous DMF with excess perchloric acid resulted in the [2:2] cyclic condensation of the constituents, providing the dinuclear Cu(II) complex [Cu2(H2R)](ClO4)2. It crystallizes in the monoclinic space group P2(1)/c, with a = 19.603(3) A, b = 13.370(2) A, c = 21.072(3) A, beta = 98.87(1) degrees, V = 5456(1) A3, and Z = 4. The ligand R4- has two N(amine)2O2 and two N(imine)2O2 metal-binding sites sharing two phenolic oxygens, and [Cu2(H2R)](ClO4)2 has the two Cu(II) ions in the N(imine)2O2 sites and two protons in the N(amine)2O2 sites. [Cu2(H2R)](ClO4)2 was converted by neutralization into [Cu2(R)], from which mixed-metal Cu(II)2M(II)2 complexes [Cu2M2(R)Cl4] (M = Co(II), Ni(II), Zn(II)) were derived. [Cu2Co2(R)Cl4]*2CHCl3*H2O crystallizes in the monoclinic space group C2/c, with a = 32.514(3) A, b = 12.246(3) A, c = 19.827(2) A, beta = 126.082(1) degrees, V = 6380(1) A3, and Z = 4. [Cu2Zn2(R)Cl4]*2CHCl3*H2O crystallizes in the monoclinic space group C2/c, with a = 32.53(1) A, b = 12.242(2) A, c = 19.729(9) A, beta = 126.03(3) degrees, V = 6354(4) A3, and Z = 4. The two complexes are isotructural and have a dimer-of-dimers structure with two separated Cu(II)M(II) units. In each dinuclear unit, the Cu(II) is bound to the N(imine)2O2 site and the M(II) is bonded to a phenolic oxygen and two nitrogens of the N(amine)2O2 site. The Cu(II) and M(II) ions are bridged by a phenolic oxygen and an exogenous chloride ion. The Cu(II)2Ni(II)2 complex has a defect double-cubane structure. Cryomagnetic studies for the Cu(II)2Co(II)2 complex indicate an antiferromagnetic spin-exchange interaction within each dinuclear Cu(II)Co(II) unit (J = -9.5 cm(-1) based on H = -2JS(Cu)S(Co)). The Cu(II)2Ni(II)2 complex shows a weak antiferromagnetic interaction between the adjacent Cu(II) and Ni(II) ions (-3.5 cm(-1)) and a weak ferromagnetic interaction between the two Ni(II) ions (+2.0 cm(-1)).

Journal Article↗
PubMed2003

Rhenium chemistry of diazabutadienes and derived iminoacetamides spanning the valence domain II-VI. Synthesis, characterization, and metal-promoted regiospecific imine oxidation.

The reaction of diazabutadienes of type R'N=C(R)-C(R)=NR', L (R = H, Me; R' = cycloalkyl, aryl) with Re(V)OCl(3)(AsPh(3))(2) has furnished Re(V)OCl(3)(L), 1, from which Re(III)(OPPh(3))Cl(3)(L), 2, and Re(V)(NAr)Cl(3)(L), 3, have been synthesized. Chemical oxidation of 2(R = H) by aqueous H(2)O(2) and of 3(R = H) by dilute HNO(3) has yielded Re(IV)(OPPh(3))Cl(3)(L'), 5, and Re(VI)(NAr)Cl(3)(L'), 4, respectively, where L' is the monoionized iminoacetamide ligand R'N=C(H)-C(=O)-NR'(-). Finally, the reaction of Re(V)O(OEt)X(2)(PPh(3))(2) with L has furnished bivalent species of type Re(II)X(2)(L)(2), 6(X = Cl, Br). The X-ray structures of 1 (R = Me, R' = Ph), 3 (R = H, R' = Ph, Ar = Ph), and 4 (R = H, R' = cycloheptyl, Ar = C(6)H(4)Cl) are reported revealing meridional geometry for the ReCl(3) fragment and triple bonding in the ReO (in 1) and ReNAr (in 3 and 4 ) fragments. The cis geometry (two Re-X stretches) of ReX(2)(L)(2) is consistent with maximized Re(II)-L back-bonding. Both ReX(2)(L)(2) and Re(NAr)Cl(3)(L') are paramagnetic (S = (1)/(2)) and display sextet EPR spectra in solution. The g and A values of Re(NAr)Cl(3)(L') are, respectively, lower and higher than those of ReX(2)(L)(2). All the complexes are electroactive in acetonitrile solution. The Re(NAr)Cl(3)(L) species display the Re(VI)/Re(V) couple near 1.0 V versus SCE, and coulometric studies have revealed that, in the oxidative transformation of 3 to 4, the reactive intermediate is Re(VI)(NAr)Cl(3)(L)(+) which undergoes nucleophilic addition of water at an imine site followed by induced electron transfer finally affording 4. In the structure of 3 (R = H, R' = Ph, Ar = Ph), the Re-N bond lying trans to the chloride ligand is approximately 0.1 A shorter than that lying trans to NPh. It is thus logical that the imine function incorporating the former bond is more polarized and therefore subject to more facile nucleophilic attack by water. This is consistent with the regiospecificity of the imine oxidation as revealed by structure determination of 4 (R = H, R' = cycloheptyl, Ar = C(6)H(4)Cl).

Journal Article↗
PubMed2005

Rhenium chemistry of azooximes: oxygen atom transfer, azoimine chelation, and imine-oxime contrast.

The concerned azooximes (L1OH, 1) are of type p-X-C6H4C(N2Ph)(NOH) (X = H, Me, Cl). The reaction of [Re(MeCN)Cl3(PPh3)2] with [Ag(L1OH)(L1O)] in cold dichloromethane-acetonitrile solvent has furnished the green colored ionized azoimine complex [ReV(O)Cl(PPh3)2(L1)](PF6), 2. In effect L1O- has undergone oxidative addition, the oxygen atom being transferred to the metal site. Upon treatment of [ReV(NPh)Cl3(PPh3)2] with L1OH in solution, the neutral azoimine complex [ReV(NPh)Cl3(L1H)], 3, resulted due to the spontaneous transfer of the oxime oxygen atom to a PPh3 ligand, which is eliminated as OPPh3. In contrast, the oxime of 2-acetylpyridine (L2OH, 4) did not undergo oxygen atom transfer and simply afforded the imine-oxime complex [ReV(NC6H4Y)Cl2(PPh3)(L2O)], 5, upon reacting with [ReV(NC6H4Y)Cl3(PPh3)2] (Y = H, Me, Cl). The spectral and electrochemical properties of 2, 3, and 5 and the structures of three representative compounds are reported. In the cation of 2 (X = H) the two PPh3 ligands lie trans to each other and the equatorial plane is defined by the five-membered azoimine chelate ring and the oxo and chloro ligands. The oxo ligand which forms a model triple bond (Re-O length 1.616(6) A) lies cis to the imine-N atom. In 3 (X = Cl) the ReCl3 fragment has meridional geometry and the imido nitrogen lies trans to the imine nitrogen of the planar azoimine chelate ring. In 5 x H2O (Y = Me), the Cl, oximato-N, and P atoms define an equatorial plane and the pyridine-N lies trans to the imido-N. The water of crystallization is hydrogen bonded to the oximato oxygen atom (O...O, 2.829(5) A). Reaction models in which chelation of the azooxime precedes oxygen atom transfer are proposed on the basis of oxophilicity of trivalent rhenium, Lewis acid activity of pentavalent rhenium, electron withdrawal by the azo group, and observed relative disposition of ligands in products.

Journal Article↗
PubMed2002

The asymmetric dialkylzinc addition to imines catalyzed by [2.2]paracyclophane-based N,O-ligands.

The first highly enantioselective dialkylzinc addition to imines in the presence of catalytic amounts of N,O-ligands is reported. N-formyl-alpha-(p-tolysulfonyl)benzylamines are the readily available starting materials easily obtained in a one-pot synthesis from benzaldehydes, formamide, and p-tolylsulfinic acid. Upon deprotonation, the sulfinate is eliminated to give the acyl imine. The acyl imines further react with alkylzinc reagents in the presence of catalytic amounts of [2.2]paracyclophane-based N,O-ligands L yielding the alkylated N-(1-phenylpropyl)formamides with excellent yields and enantioselectivities.

Journal Article↗
PubMed2003

Unfunctionalized, alpha-epimerizable nonracemic ketones and aldehydes can be accessed by crystallization-induced dynamic resolution of imines.

This paper describes an operationally simple deracemization process of aldehydes and ketones. This new crystallization-induced dynamic resolution (CIDR) protocol allows for nearly complete conversion of the racemic mixture into one enantiomer. Crystallization of imines derived from racemic ketones or aldehydes 1 and trans-(1R,2R)-1-amino-6-nitroindan-2-ol (2) afforded diastereomerically pure, crystalline imines 3. Biphasic hydrolysis of 3 then affords recovered 2 and enantiomerically enriched 1 in high yield and er (substrate, yield/ee: 2-methylcyclohexanone, 97%/92; 2-ethylhexanal, 94%/98; 2-methylcyclopentanone, 94%/98; 2-cyclohexylcyclohexanone, ND/98; 3-methyl-2-pentanone, ND/76). The scope, limitations, and industrial perspective of this process are discussed. This highly effective CIDR process is likely due to pi-stacking of 2 and a hydrogen bonding of the imine with the free hydroxyl of 2 in the solid state.

Journal Article↗
PubMed2003

Chiral bis-pi-allylpalladium complex catalyzed asymmetric allylation of imines: enhancement of the enantioselectivity and chemical yield in the presence of water.

The chiral pi-allylpalladium complex 2a, prepared from exoethylidenenorpinane 7, catalyzed the allylation of diverse imines with allyltributylstannane in the presence of 1 equiv of water in good to high enantioselectivities. The catalyst prepared from a 1:1 mixture of (E)- and (Z)-7 was found to be consisting of two stereoisomers 2a and 2b in 1.3:1 ratio. On separation, 2a catalyzed the allylation of imines in much higher enantioselectivities than 2b, giving the same major enantiomer and thereby justifying the need to separate 2a free of 2b. We have achieved the highest separation ratio of >400:1 for 2a:2b by repeated recrystallizations. Isomerization of 2b to 2a during recovery of 2a from the filtrates was observed as more of 2a was recovered each time during recrystallization. Although dry THF was the best solvent, we tried various additives and found that addition of one equivalent of water gave the best results with respect to shorter reaction time, higher yields and enantioselectivities. Thus, we have developed a more general, reproducible, robust and a non-Lewis acid catalyzed procedure for catalytic asymmetric allylation of imines under essentially neutral conditions.

Journal Article↗
PubMed2004

Imine insertion into a late metal-carbon bond to form a stable amido complex.

An arylrhodium(I) complex containing a labile dative ligand was prepared, and its reactivity toward aryl imines was investigated. The arylrhodium(I) complex (DPPE)Rh(C5H5N)(p-tol), 2, was isolated in 65% yield from [(DPPE)Rh(mu-Cl)]2, pyridine, and p-tolyllithium. Reaction of 2 with the aldimine (p-tol)CH=N(C6H4-p-CO2Me) (3a-Tol) gave the Rh amide insertion product 4 in 88% isolated yield. The solid-state structure of 4 was determined by single-crystal X-ray diffraction. The reaction of 2 with the electron-neutral and electron-rich aldimines (Ph)CH=NPh (3b) and (p-tol)CH=N(C6H4-p-OMe) (3c) also appeared to involve insertion, but the amido complexes formed from these insertions were not stable. Thus, reaction of 2 with 3b, followed by addition of Et3NHCl, gave the amine and ketimine products (Ph)(p-tol)CH-NHPh, 5, and (p-tol)(Ph)C=N(Ph), 6, in 25% and 50% yields. Several lines of data indicate that these products are formed by a sequence of transformations involving insertion of imine to give a Rh amide intermediate, beta-hydrogen elimination, cyclometalation to form a bound imine and H2, and protonolysis of the metallacycle upon addition of Et3NHCl. Consistent with this proposal, the proposed metallacycle containing the ortho-metalated ketimine ligand (p-tol)2C=N(C6H4-p-OMe) was isolated and characterized by single-crystal X-ray diffraction.

Journal Article↗
PubMed2005

A fluorobenzene adduct of Ti(IV), and catalytic carboamination to prepare alpha,beta-unsaturated imines and triaryl-substituted quinolines.

A rare fluorobenzene adduct of group 4, [(nacnac)Ti=NAr(FC6H5)][B(C6F5)4] (nacnac- = [ArNC(tBu)]2CH, Ar = 2,6-iPr2C6H3), has been isolated and structurally characterized. This highly electron-deficient system engages readily in imine metathesis and catalyzes carboamination reactions involving diphenylacetylene and aldimines to afford alpha,beta-unsaturated imines as well as triaryl-substituted quinolines. The latter product results from cyclization of the corresponding electron-rich alpha,beta-unsaturated imine.

Journal Article↗
PubMed2003

Evaluation of chiral oxazolines for the highly enantioselective diethylzinc addition to N-(diphenylphosphinoyl) imines.

On the basis of the principle that the incorporation of the structurally rigid and conformationally restricted skeleton in beta-amino alcohols is beneficial to the enantioselective diethylzinc addition to imines, a series of chiral oxazolines, which had been designed and conveniently prepared from commercially available (1S,2S)-2-amino-1-phenylpropane-1,3-diol, were applied in the diethylzinc addition to diphenylphosphinoyl imines to give high yields of 68-84% and excellent ee values of 90-95%. The configuration of the product was controlled by the chirality of the carbon bonded to the hydroxyl group in the oxazoline. Oxazolines bearing a para- or meta-substituted phenyl group generally offered higher enantioselectivity than those containing an ortho-substituted phenyl. The X-ray structures of 4f and 4j, in combination with the proposed transition state, preliminarily explained why oxazolines with a para- or meta-substituent on the phenyl group gave higher enantioselectivities than those bearing an ortho-substituent. This successful example using chiral oxazolines to promote the titled reaction implies that a large family of chiral compounds containing an oxazoline ring moiety have the potential to be developed for promoting the highly enantioselective dialkylzinc addition to N-(diphenylphosphinoyl) imines.

Journal Article↗
PubMed2004

The first catalytic asymmetric allylation of imines with the tetraallylsilane-TBAF-MeOH system, using the chiral bis-pi-allylpalladium complex.

The asymmetric allylation of imines with use of catalytic transition metals with chiral ligands should be a new frontier of the enantioselective C-C bond formation. So far allyltrimethylsilane, allyltrichlorosilane, and allyltrimethoxysilane have been commonly employed with use of either silane activators or dual silane-imine activators. However, tetraallylsilane is untouched in the allylation of aldimines. The first allylation of aldimines with the tetraallylsilane-TBAF-MeOH system with use of the bis-pi-allylpalladium catalyst under catalytic, non-Lewis acid, essentially neutral and very mild reaction conditions has been achieved. The reaction is triggered by dual activation/promotion by TBAF and MeOH in which the fluoride anion activates the C-Si bond cleavage and MeOH promotes the facile protonation of intermediate palladium amide. Thus, the synthesis of chiral homoallylamines is achieved in a shorter reaction time and higher yields and enantioselectivities through an efficient, general, and reproducible allylation protocol for imines.

Journal Article↗
PubMed1996

Stereochemical Aspects in the Asymmetric Michael Addition of Chiral Imines to Substituted Electrophilic Alkenes.

The Michael-type addition of chiral imines, derived from racemic alpha-substituted cyclanones and optically active 1-phenylethylamine, to electrophilic alkenes, in neutral conditions, constitutes one of the most efficient methods for the stereocontrolled construction of quaternary carbon centers. In order to create an additional stereogenic center at the alpha- or beta-position to the quaternary one, the behavior of a variety of alpha- and beta-substituted alkenyl acceptors was examined. In general, these additions are highly regioselective, the alkylation taking place predominantly, if not exclusively, at the more substituted alpha-side of the imine function; however, in some cases (electrophilic alkenes 28 and 49), significant amounts (10-15%) of regioisomeric adducts were obtained. With the exception of methyl propiolate 52, a remarkable control of the absolute configuration of the adducts were always observed with these Michael acceptors. According to the general rule we have previously proposed, the alkylation process takes place preferentially on the less hindered pi-face of the more substituted secondary enamine, in tautomeric equilibrium with the starting imine. An excellent diastereocontrol was always obtained by using the present alpha- and beta-substituted alkenes. These stereochemical outcomes can be interpreted by invoking that the reaction proceeds through a compact approach of the reactants, the hydrogen atom at the nitrogen center of the enamine being transferred to the alpha-vinylic carbon atom of the acceptor, concertedly with the creation of the C-C bond. In this respect the "endo-approach" 58, in which the electron-withdrawing group of the acceptor faced to the nitrogen atom of the enamine (case of acceptors 10, methyl methacrylate, 24, 28, 43, 47, and 49) largely prevails over the "exo-approach" 59 (case of acceptor 38). This predominant "endo-preference" can be reasonably interpreted in terms of a cooperative effect between steric and stereoelectronic factors.

Journal Article↗
PubMed1996

Addition of Transiently-Generated Methyl o-Lithiobenzoate to Imines. An Isoindolone Annulation.

Addition of phenyllithium to a mixture of an imine, methyl o-iodobenzoate, and BF(3).etherate at -105 degrees C gives good to excellent yields of isoindolones. The transient formation of methyl o-lithiobenzoate is proposed, which is formed by a rapid lithium/iodide exchange reaction of the phenyllithium with methyl o-iodobenzoate in the presence of the imine. The transiently generated anions can then be captured by the BF(3)-activated imines to form the isoindolones in good to high yield. The reactions conditions are sufficiently mild, and selective, to permit functional groups such carbmethoxy and aryl bromide, which could otherwise react with the added PhLi, to be tolerated.

Journal Article↗
PubMed1997

Construction of Quaternary Stereogenic Centers via [2 + 2] Cycloaddition Reactions. Synthesis of Homochiral 4,4-Disubstituted 2-Azetidinones and Imine Substituent Effects on beta-Lactam Formation.

A study on the asymmetric construction of quaternary stereogenic centers via [2 + 2] cycloaddition reaction of ketenes with ketimines is described. Reaction of achiral ketenes and chiral alpha-alkoxy ketone-derived imines resulted in formation of new beta-lactams as single diastereomers. The cycloaddition was extended to pyruvate imines, aralkyl ketone-derived imines, and dialkyl ketimines. In these cases the asymmetric induction was satisfactorily achieved using beta-silylalkanoyl ketenes and the Evans-Sjögren ketene. C,C-Bis (trimethylsilyl)methylamine ketimines derived from enolizable dialkyl ketones cleanly led to the corresponding C(4) disubstituted beta-lactams without deprotonation. Therefore, a general methodology for a convergent asymmetric synthesis of beta-lactams in which C(4) exists as a quaternary carbon is provided.

Journal Article↗