Photochemical Synthesis of 3,4-Dihydro-2H-1,3-oxazin-4-ones
24 September 2004 (online)
The first example of a C-O bond formation in the course of the Norrish-Yang reaction is described. Starting with readily accessible α-mesyloxy-β-keto amides 4, a δ-hydrogen transfer to the excited carbonyl group occurs and the diradicals thus formed undergo a very rapid elimination of methane sulfonic acid providing enolate diradicals. These ambidental enolate diradicals undergo a regioselective cyclization to 3,4-dihydro-2H-1,3-oxazin-4-ones 5. In two cases a cleavage reaction is observed, giving cyclic imines. The mechanism is investigated by means of DFT- and ab initio methods.
Norrish-Yang reaction - diradicals - oxazinones - photocyclization - heterocycles