One of the early reactions reported by Stille was the coupling of unsymmetrical
tetraalkyltins 1-53 with acid chlorides (Scheme 13). 29 The rate of transmetalation
reaction of unsymmetrical organotrimethyltin or organotributyltin (R1
SnR3) followed the
order of R1
PhC≡C > PrC≡C > PhCH=CH, CH2=CH > Ph > PhCH2 > CH3OCH2 > CH3 >
Bu, Et > i-Pr.30 This trend makes sense since these groups have to be able to stabilize the
developing negative charge in the transition state.