Selective access to sulfurated and selenated heterocycles by intramolecular cyclization of -substituted sulfides and selenides

delta-Hydroxy- and delta-amino alfa-thio-esters, easily obtainable through S-alkylation of beta-mercapto alcohols and beta-amino thiols with bromo acetate, behave as suitable starting compounds to obtain various 2-hydroxy-1,4-oxathianes and (S)-3,4-dihydro-2H-1,4-thiazines via a reductive ring closure. Under similar conditions, selenated heterocycles are also synthesized.