The reaction of alkenylisocyanide 6a and mercaptoethanol affords cis and trans pyroglutamates 16 and 17 (72%, 1: 2.5 cisltans ratio). Evidently, the product of free radical cyclization is the 2-((hydroxyethyl) thio)-A1-pyr-roline 14 shown in Scheme 3. It was originally assumed that this compound is transformed to tert-butyl4-methylpyroglutamates 16/17 through the intermediacy of the ortho derivative 15 which undergoes hydrolysis ...
