1,3‐Oxathiole and Thiirane Derivatives from the Reactions of Azibenzil and α‐diazo amides with thiocarbonyl compounds

Abstract

AbstractThe reactions of α‐diazo ketones 1a,b with 9H‐fluorene‐9‐thione (2f) in THF at room temperature yielded the symmetrical 1,3‐dithiolanes 7a,b, whereas 1b 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 (1c), thio ketones 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 1c were more sluggish than those with 1a,b, they were catalyzed either by the addition of LiClO4 or by Rh2(OAc)4. In the case of 2d in THF/LiClO4 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 trans‐9b by treatment with 1c in the presence of Rh2(OAc)4 (Scheme 4). Xanthione (2e) and 1c 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 α‐diazo amides 1d,e (Schemes 5–7). It is worth mentioning that formation of 1,3‐oxathiole or thiirane is not only dependent on the type of the carbonyl compound 2 but also on the α‐diazo amide. In the case of 1d 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‐carboxamide 11b 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 mechanism via initial formation of acyl‐substituted thiocarbonyl ylides which undergo either a 1,5‐dipolar electrocyclization to give 1,3‐oxathiole derivatives or a 1,3‐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 1,3‐dithiolane derivatives by a 1,3‐dipolar cycloaddition.