Synthesis of Stannyl Dienes

The lithium[2-tri- -butylstannyl-Z-l-alkenyl]-l-borates, prepared by copper catalyzed addition of Bu3SnB-(OCH3)-9-BBNLb to 1-alkynes (vide supra), are selectively coupled via organopalladium or organocuprate with allylbromide, exclusively at the vinyl boron bond. The process results into the exclusive or predominant formation of 5-tributylstannyl-l,4-(fi)-dienes (Chart 24.8) [38]. 

Typical of allylboranes, B-isoprenyl-9-BBN reacts with acetaldehyde with allylic rearrangement to provide the borinate intermediate via a six-mem-bered transition state [43]. The alkaline hydrogen peroxide oxidation of this intermediate affords the desired 4-methylene-5-hexen-2-ol (Eq. 24.20). Table 24.20 [41] summarizes the results of representative aldehydes with B-isopre-nyl-9-BBN. 

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