ALLYLIC OXIDATION OF OLEFINS WITH CHROMIUM TRIOXIDE-PYRIDINE COMPLEX

The allylic oxidation of 16 substituted cyclohexenes and steroids with the isolated dry CrO3-(pyridine)2 complex in methylene chloride at room temperature has been studied. The yield of enones varied from 48 to 95% (based on recovered starting material). The following generalizations were formulated: (1) allylic methyl groups are not readily oxidized; (2) if more than one allylic methylene group is present in a conformationally flexible molecule, enones resulting from attack at both positions are formed; if the molecule is conformationally rigid, like a steroid, a selectivity is found; (3) attack at an allylic methine position yields the isomeric enone where possible; similar rearrangements occur with a methylene system possessing steric hindrance. The advantages and limitations of this oxidation procedure are mentioned and the course of the oxidation is discussed on a mechanistic basis. © 1969, American Chemical Society. All rights reserved.