Azide/oxygen photocatalysis with homogeneous and heterogeneous photocatalysts for 1,2-aminohydroxylation of acyclic/cyclic alkenes and Michael acceptors

Abstract

Homogeneous as well as heterogeneous photocatalysts that are able to oxidize the azide anion with low competitive singlet oxygen quantum yields are used to generate azidyl radicals. These radicals add to electron-rich as well as electron-poor (Michael acceptors) alkenes, and carbon radicals are formed regioselectively. Trap- ping with triplet oxygen (type I photooxygenation) is diffusion controlled, and the initially formed peroxy radicals are reduced with regeneration of the photocatalyst. Fluorescence quenching studies reveal rapid photoinduced electron transfer in the first catalysis step. The lack of rearrangement products in the bicyclic terpene series (pinenes, limonene) accounts for rapid subsequent oxygen trapping and back electron transfer steps. The 1,2-azidohydroperoxidation enables synthesis of 1,2-azidoalcohols and 1,2-aminoalcohols by different reduction protocols. Substrate modification and combination of type II photooxygenation with electron transfer photocatalysis allows the synthesis of 1-amino-2,3-diols and 2-amino-1,3-diols.