1,3-Oxathiole and Thiirane Derivatives from the Reactions of Azibenzil and alpha-Diazo Amides with Thiocarbonyl Compounds

Abstract

The reactions of alpha-diazoketones la,b with 9H-fluorene-9-thione (2f) in THF at room temperature yielded the symmetrical l,3-dithiolanes 7a,b, whereas lb and 2,2,4,4-tetramethylcyclobutane-1,3-dithione (2d) in THF at 60' led to a mixture of two stereoisomeric 1,3-oxathiole derivatives cis- and trans-9a (Scheme 2). With 2-diazo-1,2-diphenylethanone (lc), thioketones 2a-d as well as 1,3-thiazole-5(4H)-thione 2g reacted to give 1,3-oxathiole derivatives exclusively (Schemes 3 and 4). As the reactions with lc were more sluggish than those with la,b, they were catalyzed either by the addition of LiCIO4, or by Rh2(OAc)4. In the case of 2d in THF/LiCIO4 at room temperature, a mixture of the monoadduct 4d and the stereoisomeric bis-adducts cis- and trans-9b was formed. Monoadduct 4d could be transformed to cis- and rrans-9b by treatment with lc in the presence of Rh2(OAc)4 (Scheme 4). Xanthione (2e) and lc in THF at room temperature reacted only when catalyzed with Rh2(OAc)4, and, in contrast to the previous reactions, the benzoyl-substituted thiirane derivative 5a was the sole product (Scheme 4). Both types of reaction were observed with alpha-diazo amides ld,e (Schemes 5-7). It is worth mentioning that formation of I,3-oxathiole or thiirane is not only dependent on the type of the carbonyl compound 2 but also on the alpha-diazo amide. In the case of Id and thioxocyclobutanone 2c in THF at room temperature, the primary cycloadduct 12 was the main product. Heating the mixture to 60", 1,3-oxathiole 10d as well as the spirocyclic thiirane-carboxamide11lb were formed. Thiirane-carboxamides 11d - g were desulfurized with (Me2N)3P in THF at 60", yielding the corresponding acrylamide derivatives (Scheme 7). All reactions are rationalized by a mecha- nism via initial formation of acyl-substituted thiocarbonyl ylides which undergo either a 1,5-dipolar electrocyclization to give 1,3-oxathiole derivatives or a I,3-dipolar electrocyclization to yield thiiranes. Only in the case of the most reactive 9H-fluorene-9-thione (2f) is the thiocarbonyl ylide trapped by a second molecule of 2f to give I,3-dithiolane derivatives by a 1,3-dipolar cycloaddition.