The Reaction of Trialkylboranes with Allyl Phenyl Ether. Syntheses of 1-Alkenes and 1,5-Alkadienes

In the organoborane chemistry, the homologation reaction is one of the useful methods for the synthesis of organoboranes not available via hydroboration.¹⁾ The allylic boranes are known to be highly reactive and exhibit specific behaviors,²⁾ but with few exceptions,³) these are difficult to be prepared directly by the hydroboration reaction.⁵⁾ Previously, we reported that in the reaction of the dianion of phenoxyacetic acid with organoborane, the phenoxy group acts as a good leaving group.⁶⁾ This result suggested us a new homologation reaction converting a saturated organoborane to a allylic borane (1) by the treatment with the carbanion of allyl phenyl ether. Here we wish to report the synthesis of 1-alkenes (II) three-carbon-homologated from starting alkenes⁷⁾ and the regioselective synthesis of 1,5-dienes (III) using allylic borane intermediates (1) (eq. 1).