Synthesis of Internal 1,3-Dienes

It is postulated that the attack of 9-BBN occurs initially from the less hindered allyl side of 29 or 30 to produce the Z isomer [A], which then rapidly rearranges through [B] to the thermodynamically more stable E isomer (31 or 32, Eq. 24.18). 

Consequently, the four possible geometric isomeric of several representative internal 1,3-dienes are synthesized (Table 24.16) [30], with high isomeric purity. 

Borane Workup Diene R R Yield (%) Isomer ratio (37 38 40 41) 

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