The nonstereospecific addition of benzeneselenenyl chloride to 3,4-dihydro-2H-pyran

Abstract

The addition of benzeneselenenyl chloride to 3,4-dihydro-2H-pyran in methylene chloride at 25 °C gives 65% of the trans and 35% of the cis Markownikoff adduct: 2-chloro-3-phenylseleno-tetrahydropyran under conditions of kinetic control. The above reaction was observed to be reversible, the adducts subsequently reacting with the benzeneselenenyl chloride under conditions similar to those used for the reaction with 3,4-dihydro-2H-pyran to give diphenyl diselenide and 2,3-dichlorotetrahydropyran in good yield. There was no evidence for the formation of 3-chloro-2-phenylselenotetrahydropyran under conditions of either kinetic or thermodynamic control. Kinetic studies support a mechanism involving a seleniranium ion that opens to an oxacarbonium ion before the product determining step.