Synthesis of Thienothiopyranthiones by a New Molecular Rearrangement

Abstract

On heating with alkynes, the readily prepared 1,3-dithioles 3 undergo a new cycloaddition reaction and an unprecedented molecular rearrangement with loss of chlorine to give the first 7H-thieno[2,3-c]thiopyran-7-thiones 4 and 4H-thieno[3,2-c]thiopyran-4-thiones 5 whose structures were confirmed by X-ray diffraction. Unexpectedly, the different alkynes used to form 3 and to convert it into 4 and 5 were incorporated regiospecifically into the thiophene and thiopyran rings, respectively. [reaction: see text]

Domino Reaction of Acyclic α,α‐Dialkenoylketene S,S‐Acetals and Diamines: Efficient Synthesis of Tetracyclic Thieno[2,3‐b]thiopyran‐Fused Imidazo[1,2‐a]pyridine/Pyrido[1,2‐a]pyrimidines

“…Initially, due to the two strongly electron-withdrawing groups at the a-positions of the ketene S,S-acetals 2, an S N V (nucleophilic vinylic substitution) type reaction [14] occurs by attack of one of the amino groups of 1,2-ethanediamine to the vinyl carbon atom of 1,3-dithiole, leading to the fragmentation of the 1,3-dithiole ring and the formation of enamine intermediate A, in which the cleavage of the C À S bond is involved. [15] It was noticeable that, in all the experiments, the amine always attacks at the vinyl carbon atom connected with the methyl group of the 1,3-dithiole during this part of the S N V reaction although the reason is currently not clear. Then, an intramolecular thio-Michael addition of intermediate B (a tautomer of A) takes place to furnish the thiopyran intermediate C. [7a,16] Next, the azatriene intermediate E would be formed by the reaction sequence of an intramolecular nucleophilic addition (C!D) and subsequent dehydration (D!E).…”

Synthesis and Reactivity of 3H-1,2-dithiole-3-thiones

“…The yields of 1,3-dithioles can vary widely from 20% to the quantitative yield. It is noteworthy that in the case of 5-chlorosubstituted dithiolethiones, rare aliphatic compounds with a usually unstable thioacyl chloride group are formed [80]. The stability of compound 35 is due to the intramolecular interaction between the thiocarbonyl group and the heterocyclic sulfur atom that can reduce the electrophilicity of the thiocarbonyl group (Scheme 35).…”

“…Surprisingly, the thiopyranthione ring is formed as a result of the reactions of 1,2dithiole-3-thiones with completely different reagents, namely, DMAD and sodium sulfide. Treatment of 4,5-dichloro-3H-1,2-dithiole-3-thione 78 (R = Cl) with excess DMAD in xylene, first at room temperature and then under reflux conditions, gave thienothiopyranethione isomers 91 and 92 in moderate yields [80]. Thus, the reaction occurs in a completely different way than in the case of 1,2-dithiole-3-thiones that do not contain two chlorine atoms as substituents (see Section 2.…”

Efficient Synthesis of Substituted Tetrahydrothiopyrano[2,3-b]thiopyran-4,5-diones by a Double Annulation Strategy from Dialkenoylketene Dithioacetals

“…In the second step, the regiospecific attack of the ethylamine amino group at the a-carbon of the vinylsulfanyl double bond in 5 triggers a nucleophilic vinylic substitution (S N V) type reaction, 12f,17 which involves the cleavage of a carbon-sulfur bond. 18 An intramolecular thia-Michael addition results in the for-mation of compounds 4. It is noteworthy that a similar S N V-type reaction was observed in our recent studies; 12f however, the reason why the amine attacks the a-carbon of the vinylsulfanyl double bond instead of the b-carbon of the carbonyl moiety still remains undiscovered.…”