I2-mediated carbamate annulation: scope and application in the synthesis of azasugars

The I2-mediated carbamate annulation provides an efficient and highly stereoselective route for the synthesis of a variety of pyrrolidines and piperidines, both in the presence and absence of protecting groups. Evidence for the formation of an iodoamine intermediate during the annulation is provided and, for the first time, we explore possible mechanisms of the annulation. The high cis-selectivity of the carbamate annulation is also compared to other N-halocyclisations and aminomercurations and some general conclusions about the diastereoselectivity of these types of reactions are made.