Radical reactions involving the loss of $N_2$

Abstract

Radical reactions involving the loss of nitrogen have been investigated. They include; (1) radical cyclization of arenesulfonylhydrazones as radical acceptors, (2) radical cyclization of $\alpha$-diazocarbonyl compounds as radical precursors, and (3) radical ring opening of gem-alkoxyazides via $\beta$-fragmentation. The radical cyclization of arenesulfonylhydrzones with Bu$_3$SnH/AIBN proceeded with the loss of N$_2$, providing unsubstituted five- and six-membered cyclic compounds in good yields. In these reactions, most of the carbon-centered radicals such as alkyl, vinyl, and allyl radicals were used as precursors. Among several arenesulfonylhydrazones, 2-mesitylsulfonylhydrazones gave the best results and mechanistic insights of this reaction have been briefly studied. Radical cyclizations of $\alpha$-diazocarbonyl compounds were conducted along with the loss of N$_2$, using diazo group as a radical precursor. In these reactions, diazomalonates, $\alpha$-diazo-$\beta$-keto esters, and $\alpha$-diazoketones have been subjected to radical reaction to afford lactones or cyclic ketones in moderate yields. Besides, relative reactivity tests between diazo group and alkyl halides revealed that the decreasing order of reactivity is iodide, diazo group, and bromide. But, the ability of diazo group as radical acceptor could not be found. Ring opening of gem-alkoxyazides under radical condition have been studied. gem-Methoxyazides, 1-azido-2-oxabicyclic compounds, and 2-azidotetrahydropyrans have been cleaved in excellent yields via $\beta$-fragmentation of tin-aminyl radicals, which were generated by the ejection of nitrogen from the azido groups. Furthermore, the effects of the substituents attached at the departing part and $\alpha$-alkoxy group on $\beta$-fragmentation have been elucidated.