DI-PI-METHANE-LIKE PHOTOREARRANGEMENTS OF ALPHA,BETA-UNSATURATED ORGANOBORANES IN THE SYNTHESIS OF BORIRENES AND BORACARBENOID INTERMEDIATES

The photoisomerization of alpha, beta-unsaturated organoboranes, either as the neutral coordination complex with tertiary amines (R3B.NR3) or as the anionic complex with organoalkali compounds (R4B-), leads, via a 1,2-shift of organic groups from boron to the adjacent carbon, to three-membered boracarbocycles or to the eventual alpha-elimination of R2 and the generation of subvalent organoboranes reminiscent of boron analogues of carbenes. These alternative reaction pathways will be illustrated by the photogeneration of the boracyclopropene ring and by the production of RB and R2B- boracarbenoids.