Preparation of 2-halogeno S-phenyl thioesters from 2-phenylsulphony -2-phenylthiooxiranes. Crystal structures of 2-phenylsulphonyloxiranes

Abstract

1-Phenylsulphonyl-1-phenylthioalkenes 8 are prepared with high stereoselectivity as (E) isomers in a one-pot process by reaction of phenyl phenylthiomethyl sulphone 9 with aldehydes, followed by elimination. Nucleophilic epoxidation of these alkenes with lithium tert-butyl hydroperoxide yields 2-phenylsulphonyl-2-phenylthiooxiranes 4 as single diastereoisomers, without detectable oxidation of the phenylthio function. The oxiranes are also prepared by treatment of phenylsuiphonyloxiranes 13 with butyllithium followed by diphenyl disulphide, which allows the preparation of 3,3-dialkyl2-phenylsulphonyl-2-phenylthiooxiranes. The oxiranes 4 react with lithium or magnesium halides to give good yields of 2-halogeno S-phenyl thioesters 5, 6 and 7. 2-lodo S-phenyl thioesters 7 are deiodinated by further treatment with magnesium iodide. In an analogous manner, 2-bromo Smethyl thioesters 15 and a 2-bromo Se-phenyl selenoester 17b are also prepared from the corresponding oxiranes. X-Ray crystal structures of 2-phenylsulphonyloxiranes 4b, 13e and 14b, reveal consistent lengthening of the C–O bond distant from the sulphonyl group, together with significant shortening of the C–O bond adjacent to the sulphonyl group.