Pyridinium Chloride in Three Membered Ring Opening. Synthesis of Chlorohydrins

Abstract

Despite the fact that pyridinium chloride has been reported¹ as a reagent in the quantitative analysis of oxiranes, we know only two examples of the use of pyridinium iodide, in pyridine, for preparative purpose. The products isolated in that solvent were the corresponding quaternary salts² derived from the iodohydrins, along with a large amount of ketone .(up to 90% in the case of 1,2-epoxycyclohexane). Even the use of a “sophisticated reagent” such as dichlorobis(benzonitrile) palladium(II) results in the formation of a good quantity (30% in the case of 1,2-epoxycyclohexane) of α-chloro ketone as byproduct.³ Unsymmetrically substituted oxiranes open under acidic conditions to give variable amounts of the two possible products according to reaction conditions. The best regioselectivity was observed, for example, using hydrogen chloride in diethyl ether