Hydroboration of 1-alkynyl(chloro)silanes - new synthons in heterocyclic chemistry

The 1-alkynyl(chloro)dimethylsilanes (RC)-C-1=C(Cl)SiMe2 [1a (R-t = Bu), 1b (R-1 = Bu-t)] react with tetraethyldiborane(6) to give the (Z)-1-chlorodim ethylsilyl-1-diethylboryl-alkenes 2a,b. These alkenes react with N- or C-li thiated azoles (pyrazole, thiazole) by LiCl elimination and formation of th e novel five-membered heterocycles 4a, 5b and 6b. In 5b and 6b, derived fro m thiazole and 4-methyl-thiazole, zwitterionic structures result which can be regarded as borane adducts of carbenes. All new compounds were character ised by H-1-, B-11-, C-13-,N-14/15- and Si-29-NMR spectroscopy (C) 1999 Els evier Science S.A. All rights reserved.