Abstract
The reactions of 1,1,3,3-tetramethyl-8-thia-5,6-diazaspirol[3.4]oct-5-en-2-one (1a) with imidazole-2-thiones 3 and pyrimidine-2(1H)-thione (6) in CHCl3 at 40 - 50° yield 2,2,4,4-tetramethylcyclobutanone dithioacetals of type 4 and 7, respectively, by interception of the intermediate thiocarbonyl ylide 2a (Scheme 2). Thiirane 5 is formed as a minor product by 1,3-dipolar electrocyclization of 2a. When thioacetamide (8a) and thiobenzamide (8b) are used as trapping reagents, the primary adduct 10 undergoes a spontaneous cyclization by intramolecular nucleophilic addition of the imino group at the carbonyl group to yield bicyclic products of type 9. The structure of 9a has been established by X-ray crystallography.
Mlostoń, Grzegorz