Intramolecular cyclisation using methyl(bismethylthio)sulphonium salts, bromine, and iodine. 5-Methylene-4,5-dihydro-oxazoles from 3-amidopropynes

Abstract

The reaction of methyl(bismethylthio)sulphonium hexachloroantimonate (3) with acylaminopropynes (1) and (2) gave (E)-5-methylthiomethylene-2-phenyl-4,5-dihydro-oxazolium (4) and (E)-2-methyl-5-methylthiomethylene-4,5-dihydro-oxazolium (7) hexachloroantimonates which were transformed into the corresponding methylenedihydro-oxazoles (10) and (13). The reaction of iodine with (1) and (2) gave (E)-5-iodomethylene-2-phenyl-4,5-dihydro-oxazolium (6) and (E)-5-iodomethylene-2-methyl-4,5-dihydro-oxazolium (9) tri-iodides which were also transformed into the methylenedihydro-oxazoles (12) and (14). The reaction of bromine with (1) gave (E)-5-bromomethylene-2-phenyldihydro-oxazole tribromide (5), which was also converted into the free base (11), while the reaction with (2) afforded ultimately 5-dibromomethyl-2-methyloxazolium bromide (25); from (25) the corresponding oxazole derivative (26) was obtained. In the reactions of both bromine and iodine with (2) some (E)-3-acetamido-1,2-dibromopropene (E)-(16) and (E)-3-acetamido-1,2-di-iodopropene (E)-(17) were also obtained.