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

Stereospecific ring opening of the sulfoxides cis-13 and trans-14 in reflux ing toluene gave the corresponding sulfenic acids 9, 10 intermediates respe ctively. The sulfenic acid 9 dimerized to the thiolsulfinate 17 by dual fun ction of the sulfenic acid as S-nucleophile/S-electrophile with loss of wat er while the sulfenic acid 10 was unchanged. The stereospecific recyclizati on of 10 to the parent sulfoxide 14 increases the higher pi-electron densit y of the double. The thermolysis of the thiolsulfinate 17 gave the transien t sulfenic acid 9, which dimerized again to repeat the process and unisolab le thioaldehyde 21. The thioaldehyde 21 was converted to either pyrrole 15 by the action of a sulfinic acid 20 catalyst formed inevitably by hydrolysi s of 17 under the reaction conditions, or thiazole 18 under neutral conditi ons. In these rearrangements, the amide carbonyl group facilitated the elim ination of a neighboring hydrogen.