PHENYL-SUBSTITUTED VINYLSTANNANES - SYNTHESIS AND REACTIVITY IN ELECTROPHILIC SUBSTITUTION-REACTIONS

Seven phenyl-substituted vinylstannanes have been prepared. (Z)-beta-( trimethylstannyl)styrene, alpha-(trimethylstannyl)styrene, and 1,1-dip henyl-2-(trimethylstannyl)ethene were prepared by Grignard coupling be tween the appropriate phenyl-substituted vinyl bromide and chlorotrime thylstannane. (E)-beta-(Trimethylstannyl)styrene and (Z)-(trimethylsta nnyl)stilbene were prepared by AIBN catalyzed hydrostannation of the a ppropriate phenyl-substituted acetylene. (E)-(Trimethylstannyl)stilben e and methyl (E)-2-(trimethylstannyl)cinnamate were prepared by pallad ium(0) catalyzed hydrostannation of diphenylacetylene and methyl pheny lpropiolate, respectively. Each compound was characterized by H-1, C-1 3, and Sn-119 NMR. Reactivity of each compound to protodestannylation was determined by spectrophotometric or H-1 NMR measurement of second order rate constants. The relative reactivity is interpreted on the ba sis of the electronic and steric effects of the phenyl substituents. T he stereochemistry of destannylation resulted in retention of configur ation for four of the compounds, consistent with an S(E)2 mechanism. H owever, methyl (E)-2-(trimethylstannyl)cinnamate gave an E/Z product r atio of essentially. This result is consistent with an allenol mechani sm for protodestannylation of this compound.