Structure of a push-pull olefin prepared by ynamine hydro-boration with a borandiol ester.

-[()-2-(2-1,3,2-Benzodioxaborol-2-yl)-2-phenyl-ethen-yl]--(propan-2-yl)aniline, CHBNO, 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 mol-ecule 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 hydro-boration of ynamines with borandiol esters is feasible. Compared to olefin hydro-boration with borane, the ynamine substrate is activated enough to undergo reaction with the less active hydro-boration reagent catecholborane.