Methods that provide rapid access to new heterocyclic structures in biologically relevant chemical space provide important opportunities in drug discovery. Here, a strategy is described for the preparation of 2,2-disubstituted azetidines, pyrrolidines, piperidines and azepanes bearing ester and diverse aryl substituents. A one-pot rhodium catalyzed N–H insertion and cyclization sequence uses diazo compounds to stitch together linear 1,m-haloamines (m = 2 to 5) to rapidly assemble 4-, 5-, 6- and 7-membered saturated nitrogen heterocycles in excellent yields. Over fifty examples are demonstrated, including with diazo compounds derived from biologically active compounds. The products can be functionalized to afford alpha,alpha-disubstituted amino acids and applied to fragment synthesis.