Conformational analysis. Part VII. 2-Alkyl-4-methyl- and 2-alkyl-2,4-dimethyl-1,3-dithiolans

Abstract

2-Alkyl-4-methyl- and 2-alkyl-2,4-dimethyl-1,3-dithiolans have been prepared and studied by means of the acid-cataysed equilibration of the diastereoisomers and ¹H n.m.r. spectroscopy. Free energy differences between diastereoisomers are small and within the range 0·13–0·54 kJ mol^–1 for the dialkyl series and 0·71–1·00 kJ mol^–1 for the trialkyl series. The data suggest that the dithiolan ring is quite a flexible system and a possible minium energy conformation can be defined only if there is a bulky substituent at the 2-position.