Formation of 1,3-oxaselenoles via Pummerer reaction in selenium dioxide oxidation of cyclic 1,2- and 1,3-diketones, and the preparation of 1,5,5-trimethyl-7-selenabicyclo [2.2.1] heptane-2,3-dione

Abstract

4,5,6,7-Tetrahydro-4′,4′,6,6-tetramethylspiro[1,3-benzoxaselenole-2,1′-cyclohexane]-2′,4,6′-trione and related 1,3-oxaselenole derivatives, and not the previously reported selenoxides of type (1), are formed in the selenium dioxide oxidation of cyclohexane-1,3-dinoes. The structural assignments were made on the basis of n.m.r. spectroscopy, and in the case of (5), X-ray analysis was undertaken. Oxidation of 3,3,5,5-tetramethylcyclohexane-1,2-dione with selenium dioxide yielded the bis-selenide (9) and the 1,3-oxaselenole (10) along with the usual oxidation products, whereas the oxidation of 3,5,5-trimethylcyclohexane-1,2-dione gave the title, bridged selenabicyclic compound.