Erste Synthese eines Benzodihydroborets

Article abstract of DOI:10.1016/0022-328X(88)80522-9

The alkali metal mediated 1,4-cyclization of <2-(bromomethyl)phenyl>boranes, which yields B-alkyl- and dialkylamino substituted dihydrobenzoboretes, has been investigated.The unknown starting materials for the cyclizations are made by selective monoalkylation or -amination of the <2-(bromomethyl)phenyl>dichloroborane (5) with tetramethyl stannane (giving 6a), t-butyllithium (giving the isobutylborane 6b), and diisopropylamine (giving 6c).Only 6c cyclizes, either to the dihydrobenzoborete 7 (with lithium) or its dimer tetrahydrodibenzo<1,5>diborocine 9 (with potassium).The bora-o-quinodimethane derivative 8, being a valence isomer of 7, could not be trapped.Reaction of 7 with the electrophile boron trichloride yields the ring-opening product 10, with hydrogen chloride a cyclic dichloroborate 12.