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[reaction: see text] Heteroaromatic thioethers and aryl, heteroaryl, and alkenylstannanes participate in a palladium-catalyzed, copper(I)-mediated cross-coupling reaction at 50 degrees C in THF.
The stannylcupration of allenes and alkynes has emerged as a powerful tool for the synthesis of allyl- and vinylorganostannanes. The regio- and stereoselectivity of this reaction depends upon the nature of the cuprate, the temperature and the structure of the allene or alkyne. The versatility and synthetic scope of the tin-synthons thus obtained is very wide. These intermediates have been employed as precursors in the key step of the stereoselective synthesis of many natural products, heterocycles or conjugated polyenes. This tutorial review shows a general survey of the recent advances in this area together with the contribution of our lab to this field.
Platinum compounds containing the ligand 1,2-diaminocyclohexane (DACH) such as tetraplatin [PtCl4(DACH)] have been found to be active in cisplatin-resistant tumour models. In an attempt to develop novel metal-based drugs with a different therapeutic profile to cisplatin, we have synthesised a series of tin compounds containing the DACH ligand, including the Sn analogue of tetraplatin [SnCl4(DACH)], and the di- and monoorganotin complexes [Ph2Sn(OAc)2(DACH)], [Bu2Sn(OAc)2(DACH)], [PhSnCl3(DACH)], [BuSn(OAc)3(DACH)], [BuSnCl3(DACH)], and [PhSn(OCOCF3)3(DACH)]. Mossbauer and IR spectroscopy indicates that the Sn(DACH) complexes are hexacoordinated with a molecular structure similar to that of tetraplatin. These compounds were tested for potential antitumour activity against a panel of human tumour cell lines, (SW620, SW1116 colon carcinoma, ZR-75-1 breast carcinoma, HT1376 bladder carcinoma, SKOV-3, PA-1 ovarian carcinoma). [Ph2Sn(penicillinate)], [Ph2Sn(OCOCH2NCOCH2NH2)], [Ph2Sn(OAc)2] were included for comparison. The results show that whereas [SnCl4(DACH)] and the monoorganotin complexes had limited or no activity, the diorganotin DACH complexes were cytotoxic with an associated increase in potency on going from diphenyl to dibutyltin, with mean IC50 values of 7.26+/-4.09 micromol ml(-1) for [Ph2Sn(OAc)2(DACH)] and 2.58+/-0.83 micromol ml(-1) for [Bu2Sn(OAc)2(DACH)] across the cell line panel. Comparison with [Ph2Sn(OAc)2] (IC50 0.69-0.43 micromol ml(-1)) indicated that addition of the DACH ligand resulted in a decrease in cytotoxicity but increased differential toxicity across the cell line panel. These results indicate that the diorganotin DACH complexes merit further investigation as potential metal-based antitumour drugs.
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[reaction--see text] A series of novel 6-endo [4 + 2] and 7-endo [5 + 2] radical-mediated annulation reactions are described. These annulation sequences involve an intermolecular radical addition followed by intramolecular trapping with an allyltin moiety incorporated into the radical precursor fragment. This methodology allows for access to functionalized 6- and 7-membered carbocycles as well as bicyclic compounds with good to excellent levels of stereocontrol.
[reaction: see text] Bu2Sn(OTf)H (1a), easily prepared from Bu2SnH2 and TfOH, was found to be very valuable for highly regio- and stereoselective hydrostannylation of various propargyl alcohols leading to (Z)-gamma-stannylated allyl alcohols. The stannylation with 1a is applicable to the synthesis of hydroxy-substituted (Z)-vinylstannanes from terminal alkynes bearing a hydroxy group at the homoallylic or bishomoallylic position. The coordination of the hydroxy group to the Lewis acidic tin center plays an important role for the observed regio- and stereochemistry.
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Nonstabilized azomethine ylides (i.e. those bearing only hydrogens or alkyl groups) can be generated from (2-azaallyl)stannanes and (2-azaallyl)silanes through an intramolecular N-alkylation/demetalation cascade. The resulting ylides undergo [3+2] cycloaddition with electron-poor or electron-rich dipolarophiles yielding indolizidines and related 1-aza[m.3.0]bicycloalkane systems in good yield. An in situ protocol allows for a one-pot, three-component synthesis of indolizidines. The (2-azaallyl)stannanes tolerate enolizable hydrogens in these cycloadditions, while (2-azaallyl)silanes do not. The mechanism of the cycloaddition cascade is clarified by a series of control experiments. The same (2-azaallyl)stannanes may be transmetalated by n-butyllithium to generate 2-azaallyllithiums, which also may undergo a [3+2] cycloaddition/N-alkylation cascade to form indolizidines.
The toxicology of tin is almost entirely the toxicology of the organic compounds of tin, for the metal itself and its inorganic compounds appear to be nearly harmless for practical purposes. Furthermore, the neurotoxicity of organotin is essentially that of trimethyltin and triethyltin.
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In order to evaluate the toxicity of the fungicide triphenyltin acetate (TPTA) on hatching, survival, morphology, and histology of early life stages of zebrafish (Danio rerio), newly fertilized eggs were exposed to concentrations of 0.5, 5, 25, 75, and 100 microg/liter TPTA for 96 h at 28+/-0.5 degrees C. Embryos and larvae were kept under constant observation for up to 7 days and studied with respect to mortality and teratogenic effects as well as histological and cytological alterations in the liver as endpoints of sublethal toxicity of TPTA. Exposure to TPTA caused dose- and time-related effects with respect to all parameters investigated: (1) Hatching was delayed at concentrations >/=0.5 microg/liter TPTA; (2) mortality increased at >/=25 microg/liter TA after 96 h exposure, with TPTA toxicity being higher in larval than in embryonic stages; (3) from >/=25 microg/liter, larvae exhibited skeletal malformation, retarded yolk sac resorption, and edema in the heart and yolk sac regions; and (4) histo- and cytopathological alterations of larval liver included changes in nuclei and mitochondria as well as glycogen depletion from >/=0.5 microg/liter TPTA. The study thus demonstrates not only an elevated sensitivity of zebrafish embryos to TPTA in stages prior to hatching, but also the importance of continuous observation over extended periods after termination of the actual exposure for a comprehensive evaluation of the toxicity of chemical compounds.
[reaction: see text] The condensation between a functionalized allylstannane and alpha-alkoxyaldehydes allows rapid access to complex and selectively protected trihydroxylated synthons. The stereocontrol of this process is strongly dependent upon the nature and the amount of the Lewis acid employed.
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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.
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