Organocatalyzed Skeletal Editing of Unstrained Rings via Wolff-type Rearrangement: Modular Synthesis of BN- Isosteres and [1,2]- Azaborines

Abstract

Herein, we report a rare example of organocatalyzed skeletal editing of unstrained rings (n = 4–8) to ring-expansion via Wolff-type rearrangement and through regioselective fixation of carbon and nitrogen atom. Strategy employed 2-formylarylboronic acid as C-B surrogate and TMSN3 as an exogenous single nitrogen source; allowed the de novo rapid synthesis of BN isosteres by forging C-C, C-N and B-N bonds under single operation. The developed method proved to be compatible with wide substrate scope (50 examples) including cyclic ketones and diverse heterocycles afforded 1C ring expanded [1,2]-azaborines. Reaction was also effective to acyclic ketones to give BN naphthalene isosteres. Control experiments and DFT study dictate the plausible reaction pathways following [1,2]-C-C/C-H shift, analogous to Wolff rearrangement.