Von organometallisch substituierten Alkenylboranen zu Alienen und 3-Borolenen / From Alkenylboranes Bearing Organometallic Substituents to Alienes and 4-Borolenes

Alkenylboranes bearing organometallic substituents (E)—Me M(R )C=C(Et)BEt [M = Sn, R = H (la), Me (lb); M = Pb, R = Me (2a), PbMe (2b)] react with alkynyllead compounds Me Pb—C=C—R [R = Me (3a), 'Bu (3b), PbMe (3c)] to give either alienes (5) or 3-borolenes (7), depending on the nature of R . 3-Borolenes are observed for R = Me and diene derivatives were identified in the reaction mixtures as intermediates, consistent with mechanistic suggestions. Only one of the two possible diastereomers of the allene 5b (from la and 3b) is formed. The products have been characterized by multinuclear NMR spectroscopy ( H, B, C, Sn and Pb NMR). In the case of 5c (from 2b and 3c), a homonuclear two-dimensional Pb COSY NMR spectrum serves for the assignment of the Pb resonances of diastereomers.