Palladium-Catalyzed Insertion of Alkynes into the Sn−B Bond of a 2-Stannyl-2,3-dihydro-1H-1,3,2-diazaborole and X-ray Structure Analyses of 1,3-Di-tert-butyl-2[(Z)-2-phenyl-2-trimethylstannylethenyl]- 2,3-dihydro-1H-1,3,2-diazaborole and 1,3-Di-tert-butyl-2[(Z)-1-ethyl-2-phenyl-2- trimethylstannylethenyl]-2,3-dihydro-1H-1,3,2-diazaborole

Abstract

Reaction of equimolar amounts of 1,3-di-tert-butyl-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (1) with a series of alkynes R1−C⋮C−R2 (2) (a: R1 = H, R2 = Ph; b: H, 4-ClC6H4; c: H, 4-BrC6H4; d: Ph, Ph; e: Me, Ph; f: Et, Ph; g: H, n-C4H9; h: Et, Et; i: H, n-C6H13) in the presence of a catalytic amount of [Pd(PPh3)4] (2 mol %) regioselectively afforded high yields of the alkenes (Z)-R1[B]CC(R2)SnMe3 (3a−h) ([B] = as the result of a cis-addition of the BSn bond of 1 to the acetylenic triple bond of 2. Spectroscopic evidence and X-ray structural analyses of 3a and 3f revealed that the bulky borolyl unit was added to the least sterically hindered end of the CC multiple bond.