Oxidation of alkyl phenyl selenides, tellurides, and telluroxides with meta-chloroperbenzoic acid for a facile and novel transformation of C-Se and C-Te bonds to C-O bonds

Abstract

In sharp contrast to the well-known selenoxide elimination leading to olefins, the treatment of alkyl phenyl selenides (PhSeR) with an excess of meta-chloroperbenzoic acid (MCPBA; 2–5 equiv. to a selenide) in alcohol at room temperature affords the corresponding dialkyl ethers by the substitution of a phenylselenium (PhSe) moiety with an alkoxy group. A similar reaction proceeds by using alkyl phenyl tellurides (PhTeR) and telluroxides [PhTe(O)R], a facile substitution of PhTe or PhTe(O) moiety by an alkoxy group being observed. Methanol is the most appropriate solvent for these oxidations and alkyl methyl ethers are formed in excellent yields. The reaction is accompanied by phenyl migration when applied to some selenides, tellurides, and telluroxides having a phenyl group at a vicinal position to the PhSe, PhTe, or PhTe(O) moiety. Application to the methoxyselenation and methoxytelluration products of cyclohexene and cycloheptene results in a ring-contraction to afford the dimethyl acetals of cyclopentane- and cyclohexane-carbaldehyde, respectively. In case of an allylic phenyl selenide, a [2,3]sigmatropic rearrangement giving a rearranged allylic alcohol occurs in much preference to the substitution by the methoxy group. Other oxidizing agents than MCPBA such as NalO₄, H₂O₂, t-BuOOH, and ozone are generally ineffective under similar conditions. It is proposed that the reaction mainly takes place as follows. Alkyl phenyl selenone, alkyl phenyl tellurone, or the MCPBA addition product to them is formed as a reactive intermediate in which an alkyl C–Se or alkyl C–Te bond fission occurs heterolytically by a nucleophilic attack of alcohol, sometimes accompanied by a 1,2-shift of the β-substituent, i.e., phenyl migration and ring-contraction.