THE GENERATION OF NITROGEN RADICALS AND THEIR CYCLIZATIONS FOR THE CONSTRUCTION OF THE PYRROLIDINE NUCLEUS

Many of the conditions necessary for the incorporation of nitrogen centered radicals in synthesis have been met. Several precursors exists that can be used to generate monoalkyl and dialkyl aminium cation radicals as well as amidyl radicals under relatively mild conditions. An important advancement was the extension of Barton's pyridine-2-thioneoxycarbonyl group (PTOC) protocol to the production of various nitrogen centered radicals. The PTOC precursors to nitrogen radicals appear to be as useful as the PTOC ester precursors for carbon radicals, especially in light of the variety of trapping agents available to functionalize the product carbon radicals formed by cyclizations and addition reactions of nitrogen radicals. The relative rate constants for competitive reactions involving nitrogen radicals and, in some cases, absolute rate constants are known; these allow design of efficient nitrogen radical chain reactions. Based on the many ring constructions demonstrated in this chapter, it is expected that the applications of nitrogen radical reactions in synthesis will become more common. © 1993, Academic Press Inc. All rights reserved.