Thermal rearrangement of 1,3-thiazolidine sulfoxides: Thiolsulfinate and thioaldehyde intermediates

Abstract

Stereospecific ring opening of the sulfoxides cis-13 and trans-14 in refluxing toluene gave the corresponding sulfenic acids 9, 10 intermediates respectively. The sulfenic acid 9 dimerized to the thiolsulfinate 17 by dual function of the sulfenic acid as S-nucleophile/S-electrophile with loss of water while the sulfenic acid 10 was unchanged. The stereospecific recyclization of 10 to the parent sulfoxide 14 increases the higher pi-electron density of the double. The thermolysis of the thiolsulfinate 17 gave the transient sulfenic acid 9, which dimerized again to repeat the process and unisolable thioaldehyde 21. The thioaldehyde 21 was converted to either pyrrole 15 by the action of a sulfinic acid 20 catalyst formed inevitably by hydrolysis of 17 under the reaction conditions, or thiazole 18 under neutral conditions. In these rearrangements, the amide carbonyl group facilitated the elimination of a neighboring hydrogen.