DABN Borazabicycles: Formation from MIDA Boronates and Synthetic Utility
We report that coordinative hemilability allows the MIDA amine to behave as a nucleophile to intercept π-allyl intermediates. A mechanistic investigation indicates that this rearrangement proceeds through an SN2-like displacement at tetrasubstituted boron to furnish novel DABN (2,8- dioxa-5-aza-1-borabicyclo[3.3.1]nonane-3,7-dione) boronates. Oxidative addition into the N-C bond of the DABN scaffold reverses the reaction and furnishes borylated π-allyl intermediates that can then be trapped with complete linear selectivity. DFT calculations indicate that stabilizing interactions in the transition state, as well as the steric bulk of the MIDA unit, are the origins of the excellent regioselectivity. We further demonstrate the utility of our new reagents by way of a 3-component coupling that features allylammonium DABN boronates as linchpin reagents. This report disseminates a previously unknown aspect of MIDA boronates that can now be exploited.