Reaction of 2,3-Dihydro-1H-1,3,2-diazaboroles and Diphenylketene: A Novel Synthesis of 1,3,2-Oxazaborolidines

Reaction of equimolar amounts of diphenylketene with a series of 1,3-di- tert -butyl-2,3-dihydro-1 H -1,3,2-diazaboroles [X = Br ( 1a ), F ( 1b ), NH 2 ( 1c ), NMe 2 ( 1d ), Me ( 1e ), SnMe 3 ( 1f ), CH C(SnMe 3 )C 6 H 4 -4-Cl ( 1g )] regioselectively afforded good yields of the 1,3,2-oxazaborolidines ( 2a − g ). The X-ray structure analysis of 2d revealed an essentially planar five-membered heterocycle with a long B−O bond and a strong exocyclic BN−π bond.