Radical reaction of alkyl azides

Abstract

Radical reaction of alkyl azides has been studied for carbon-nitrogen bond formation. First, the use of alkyl azides as radical acceptors was investigated. Our approach relied on the intramolecular addition of an alkyl radical to an azido group, followed by the loss of nitrogen to produce an aminyl radical. Intramolecular addition of alkyl radicals to the azido group afford 5- and 6-membered N-heterocycles in high yields. With Bu$_3$SnH/AIBN, only the iodide could be used as a radical precursor, whereas the iodide, bromide, thionocarbonate, and ketone could be utilized as a radical precursor with (TMS)$_3$SiH/AIBN. Several tandem cyclizations were achieved by using the azido group as a radical acceptor. Our attention was next given to the use of the alkyl azides as radical precursors, and our approach relied on the intermoleclar addition of the tributyltin radical to the azides to generate the tributyltin substituted aminyl radicals. The radical reaction of the acyclic keto azides under the standard reaction condition (Bu$_3$SnH/AIBN) afforded the acyclic amides in quantitative yields, via 1,5- or 1,6-acyl group transfer from carbon to nitrogen. The radical reaction of the cyclic keto azides with Bu$_3$SnH/AIBN afforded the ring expansion products, macrolactams, in high yields via $\beta$-fragmentation of the intermediate alkoxy radicals. Intramolecular addition of the aminyl radical to the aziridinylimine bond was examined. The radical reaction of the azido aziridinylimines with a catalytic amount of Bu$_3$SnH and AIBN afforded the cyclic imines in high yields.