Diastereoselective synthesis of 3,6-dihydro-2 H-1,3,4-thiadiazines

Abstract

Thionation of the benzil hydrazones 3 with Lawesson's reagent afforded the 3,6-dihydro-2 H-1,3,4-thiadiazines 4 by an intramolecular cyclisation. This reaction was shown to be diastereospecific and allowed the formation of the exo compounds 4b– e. When the homochiral SAMP–hydrazone 3f was used, the reaction afforded enantiomerically pure (4 R,6 R,9 S)- 4f.