Lewis-acid-catalysed oxygenation of 1,1'-bicyclohexenyl and α-terpinene. Reactions in dichloromethane and liquid sulphur dioxide

Abstract

1,1'-Bicyclohexenyl and α-terpinene are converted into the corresponding cyclic peroxides in the presence of oxygen and Lewis acids in dichloromethane. In liquid sulphur dioxide under oxygen, the . major product from 1,1'-bicyclohexenyl in the presence of SnCl₄, SbF₅, and SbCl₅, is the corresponding cyclic sulphone, whereas the cyclic peroxide is almost exclusively formed in this medium with MoCl₅, WCl₆ and VOCl₃. Under the same conditions, α-terpinene is quantitatively oxygenated in a dark reaction, in the absence of added Lewis acids. In a 1 : 1 dichloromethane-sulphur dioxide medium, ergosteryl acetate requires irradiation for conversion into the corresponding peroxide. Mechanistic interpretations of these observations are presented.