Serendipitous synthesis of 2-alkenyl- and 2-aryl-4-thiazolidinones using dithiodiglycolic anhydride

Cyclic anhydrides, including sulfur-embedded anhydrides such as thiodiglycolic anhydride, are useful dipolar synthons for the synthesis of complex organic molecules through formal cycloaddition reactions with imines (i.e., the Castagnoli-Cushman Reaction (CCR)). Here, we disclose that a disulfide-embedded anhydride (i.e., dithiodiglycolic anhydride) unexpectedly underwent an efficient formal cycloaddition with aryl aldimines to afford functionalized 4-thiazolidinones, without complications arising from the CCR. Importantly, when 1,3-azadienes were employed, the 2-alkenyl-4-thiazolidinones were obtained without complications stemming from the sulfa-Michael reaction or the Tamura reaction. These 4-thiazolidinones constitute the core of several pharmaceuticals that display a broad spectrum of biological activities, including anti-HIV and anticancer. The current tactic obviates the need for thioglycolic acid, an alternative annulation partner associated with a strongly unpleasant odor. The ensuing N,S-heterocycles are then engaged in several selective fragment growth processes, including oxidation to sulfoxides, sulfones, and epoxysulfones.

Automated summary

This study reveals that dithiodiglycolic anhydride can undergo formal cycloaddition with aryl aldimines to yield functionalized 4-thiazolidinones. 2-alkenyl-4-thiazolidinones can be obtained when 1,3-azadienes are used. These compounds serve as the core structure of various pharmaceuticals with diverse biological activities.