Thiopyrans from enamines

Starting from enamines of methyl ketones (30), 4,6-disubstituted thiopyran-2-thiones (8) are obtained ... 

Enamines derived from thiopyran-3-one, although tautomeric, tend to exist predominantly in conjugation with the sulfur atom the Fischer indole reaction, when applied to that ketone, affords solely the systems fused 2,3 on to the thiopyran (Scheme 10) (76CL5). 4-Amino-3,4-dihydro-2Ff-thiopyrans readily eliminate ammonia or amines on heating or treatment with acid, with formation of 2H- thiopyrans <78CR(C)(286)553). 

The imines derived from 3-hydroxynaphtho[l,8-c]thiopyran-2-carbaldehyde and the corresponding 2-acetyl compound exist in solution in the keto-enamine 270, R1 = H, shown (Scheme 24). Irradiation at 436 nm results in reversible Z -E isomerization about the exocyclic double bond <1995ZOR1559>. 

Enamines (92) with l,2-dithiole-3-thiones unsubstituted in the 5-position give thiopyrane-2-thiones (93).147,148 Formation of thiopyrane-2-thiones (94) from enolate ion 95 has been described.149... 

A recent paper describes syntheses of 2ff-thiopyran 1,1-dioxides, for example (25), starting with enamines (24). This reaction sequence has also been applied to enamines prepared from cyclic ketones. 

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