Boron-homologation reactions represent an efficient and programmable approach to prepare alkylboronates, which are valuable and versatile synthetic intermediates. The typical boron-homologation reaction, also known as the Matteson reaction, involves formal carbenoid insertions into C−B bonds. Here we report the development of aza-Matteson reactions via carbenoid insertions into the N−B bonds of aminoboranes. By changing the leaving groups of the carbenoids and altering Lewis acid activators, selective mono-and double-methylene insertions can be realized to access various αand β-boron-substituted tertiary amines, respectively, from common secondary amines. The derivatization of complex amine-containing bioactive molecules, diverse functionalization of the boronate products, and sequential insertions of different carbenoids have also been achieved.