Stille reaction triple couplings

Let us close this section with a gold- and palladium-cocatalyzed carbostannylation of substituted propiolates 89 by vinylstannanes 90 (Scheme 45) [81]. The Au(I) electrophilic activation of the triple bond is said to promote the oxidative addition of the Pd(0) to the alkyne. Next, a transmetallation of the vinylstannane across one of the Pd-C bonds puts the reaction back on a Stille-type track. Several a-stannylated dienic esters such as 91 were thus prepared in medium to good yields. The stereocontrol is similar to that observed in the Stille coupling (high syn selectivity for the addition and stereospecificity with respect to the vinylstannane), albeit some stereochemical leakage was observed with bulky Z-stannanes. 

Some palladium-catalyzed reactions of organotins, such as carbostannylations, are not related to the Stille cross-coupling. The history of the transition-metal-cata-lyzed carbostarmylation [148] began with alkynylstannylation of alkynes catalyzed by a palladium-iminophosphine complex [149]. Thus, alkynylstannanes added to a carbon-carbon triple bond of various acetylenes, conjugated ynoates and propar-gyl amines and ethers in the presence of a catalytic amount of a palladium-iminophosphine complex [150]. The reaction also proceeded with arynes to afford ortho-substituted arylstannanes, which could further be converted into 1,2-substituted arenes via carbon-carbon bond-forming reactions [151]. 

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