Cyclizations of N-Stannylaminyl Radicals onto Nitriles (original) (raw)

Stannylaminyl radicals derived from radical reactions of Bu 3 SnH with azidoalkylmalononitriles exhibit highly efficient 5-and 6-exo cyclization onto either nitrile group to give aminoiminyl radicals that in turn are reduced to amidines or undergo successive 5-exo cyclization onto an internal alkene. Radical cyclization reactions have become a powerful tool for the construction of carbocyclic and heterocyclic systems, even those occurring in natural products. 1 Radical cyclizations most often involve carbon-carbon bond formation, whereas those leading to carbon-nitrogen bonds are much less documented. The reported methods rely on additions of aminyl 1e,2 and iminyl 1e,3 radicals to CdC and CdO double bonds or additions of carbon radicals to nitrogen atoms of imines. 1e,4 The synthetic potential of azide radical reactions has so far been rather poorly investigated, though the reported studies have revealed that the azido moiety can act as a valuable radical acceptor toward carbon-and heteroatomcentered species to yield an aminyl radical after loss of molecular nitrogen by the initial triazenyl adduct. 2e,f,5 Indeed, intramolecular additions of aryl, 6 thiocarbonyl, 7 alkyl, 8 vinyl, 9