Organostannanes Lewis acid promotion

Lewis acids catalyse the addition of allylic organostannanes or organosilanes to aldehydes. In contrast to the thermal reactions of allylboranes or allylstannanes, the use of a Lewis acid promotes reaction via an acyclic transition state. With a y-substituted allylsilane, such as crotyltrimethylsilane 156, the E-isomer reacts with excellent selectivity for the syn product (1.149). The corresponding Z-isomer (of 156) also favours the syn product, although with reduced selectivity (64 36). The transition state is thought to involve the ahgnment of the two tt-bonds 180° to one another (1.150). 

MECHANISTIC VARIABILITY IN THE LEWIS ACID-PROMOTED REACTIONS OF ALDEHYDES WITH ORGANOSTANNANES... 

Other reactions of organostannanes. Hydrostannylation of allenes catalyzed by Pd(0) is regiochemically distinct from reactions promoted by Lewis acids [e.g.,... 

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