Reactions of Fused Carbonyl-containing Spirodihydrofurans with Hydrogen Sulfide and Acids

Reactions were studied of fused spirodihydrofurans originating from 1,3-cyclohexanedione with hydrogen sufide arising in situ. Depending on a substituent at the atom C ³ of the heterocycle the reaction ended by thionation of the conjugated carbonyl group followed by heterocyclization involving the spirodimedonyl fragment. A quantum-chemical forecasting of the protonation stages of substrates and their thionated analogs was performed applying the semiempirical PM3 procedure. A probable mechanism of investigated transformations of the spirodihydrofurans was suggested.