Synthesis, characterisation and reactivity of 2-functionalised vinylstannanes

The functionalised vinylstannanes of the type (E)/(Z)-Ph3SnCR ' =CHYRn and (E)/(Z)-Ph3SnC(YRn)-CHR ' (YRn = NMe2, OEt, SMe, SEt; R ' = Ph, Bu (n-butyl), Pe (n-pentyl), H) were prepared by non-catalysed or Pd-catalysed hydrostannylation reactions. Particular stereoisomers were isolated by means of preparative HPLC and fully characterised using H-1-, C-13(-) and Sn-119-NMR spectroscopy. The reactions of 2-functionalised vinylstannanes (E)/(Z) -Ph3SnCR ' =CHYRn, with acetic and chloroacetic acid in CDCl3 proceeded by protodestannylation yielding Ph3SnOOCCH2X (X = H, Cl) and CHR ' =CHYRn. The results of kinetics measurements reveal that Lewis-basic substituents YR,, facilitate the electrophilic cleavage of Sn-C= bonds, and this effect increases with the basicity of the heteroatom Y, i.e. in the order S < O < N. In contrast, an alkyl substituent at the cc-carbon atom slightly suppresses the reaction rate. Furthermore it was found that the E-isomers react faster than the corresponding Z-isomers. (C) 2001 Elsevier Science B.V. All rights reserved.