Structure of a push–pull olefin prepared by ynamine hydroboration with a borandiol ester

Abstract

N-[(Z)-2-(2H-1,3,2-Benzodioxaborol-2-yl)-2-phenylethenyl]-N-(propan-2-yl)aniline, C23H22BNO2, contains a C=C bond that is conjugated with a donor and an acceptor group. An analysis that included similar push–pull olefins revealed that bond lengths in their B—C=C—N core units correlate with the perceived acceptor and donor strength of the groups. The two phenyl groups in the molecule are rotated with respect to the plane that contains the BCCN atoms, and are close enough for significant π-stacking. Definite characterization of the title compound demonstrates, for the first time in a reliable way, that hydroboration of ynamines with borandiol esters is feasible. Compared to olefin hydroboration with borane, the ynamine substrate is activated enough to undergo reaction with the less active hydroboration reagent catecholborane.