Thioketones enamines

In the case of primary (and secondary ) )S-keto enamines, the enamino keto form 30a or 31a is stabilized by its push-pull conjugated mesomeric form 30b or 31b and by an intramolecular hydrogen bridge which dominates over the tautomeric imino enol form 30c or 31c (equation 3). Similar results are reported for jff-thioketone enamines . ... 

The cyclic thioketone, 3-oxotctrahydrothiophene (11), gives a mixture of enamines (12,13) when caused to react with a secondary amine such as piperidine or pyrrolidine (31). The enamine mixture can be reduced to the 3-aminotetrahydrothiophene using formic acid or oxidized to the 3-amino-thiophene using diisopentylsulfide. 

When enamines are employed as sulfene traps, thiete 1,1-dioxides (e.g. 142) can be prepared by subsequent Hofmann elimination of amine. An alternative route to thiete 1,1-dioxides involves trapping sulfenes with ynamines, as illustrated by preparation of (144) (73S534). Certain thietes such as (145) (80LA873, 78TL3617, 78TL4839) are available directly from thioketones by 2 + 2 photocycloaddition with alkynes. 

But the more heteroatoms, the more alternatives. We could disconnect the enamine first 27a and the C-S bond second 31. This suggests a reasonable a-halo-ketone 33 and an unstable-looking imine 32. Fortunately this is just a tautomer of the thioamide 34. Though thioketones are unstable, thio-amides are stable thanks to extra conjugation. 

Furthermore, the enamines (208) react with 2-methylthio-l,3-dithiolylium salts (207) in the presence of triethylamine to give addition products which lead to the ketone (209a) upon hydrolysis or the thioketone (209b) by hydrosulfolysis (75JPR137). 

Similarly small rate factors were obtained for 1,3-dipolar cycloadditions between diphenyl diazomethane and dimethyl fumarate [131], 2,4,6-trimethylbenzenecarbonitrile oxide and tetracyanoethene or acrylonitrile [811], phenyl azide and enamines [133], diazomethane and aromatic anils [134], azomethine imines and dimethyl acetylenedi-carboxylate [134a], diazo dimethyl malonate and diethylaminopropyne [544] or N-(l-cyclohexenyl)pyrrolidine [545], and A-methyl-C-phenylnitrone and thioketones [812]. Huisgen has written comprehensive reviews on solvent polarity and rates of 1,3-dipolar cycloaddition reactions [541, 542]. The observed small solvent effects can be easily explained by the fact that the concerted, but non-synchronous, bond formation in the activated complex may lead to the destruction or creation of partial charges, connected... 

The reaction of thialdehyde and thioketone 5,5-dioxides, generated in situ from sulfonyl chlorides, with enamines leads to a mixture of cis- and /rum-substituted 3-aminothietane 1,1-dioxides 111. The pure frans-isomers are obtained by stirring the isomeric mixtures obtained with a catalytic amount of potassium fe/7-butoxide in tert-butyl alcohol for one day to two weeks. 

Inspection of empirical formulas and the corresponding structures of starting material and product reveals that III is solely a dimer of I. Two important facts, however, conspire against this outer-layer simplicity. First, if the deep-blue compound I is allowed to dimerize by itself (and this in fact occurs in solution), the colorless dimeric structure IV (but not III) results. Second, there is an enamine in the medium, which obviously makes the difference. The role of this enamine should not be taken lightly, particularly if the conjugation of the sulfur atoms in I imbues this compound with a behavior reminiscent of oxygen homolog systems, that is, quinonoids. The exocyclic double bond is amenable to a Michael-type 1,4 addition by suitable nucleophiles while the thioketone sulfur is potentially a nucleophilic center (see Scheme 28.1). 

Enamines 186 also react with 2-methylthio-1,3-dithiolium cations 187. In chloroform, in the presence of triethylamine, an addition product is formed which leads to the ketone 188 by hydrolysis or to the thioketone 189 by hydrosulfolysis. ... 

The most obvious disconnection (1,1-diX) of a thiazole 43 reveals an acid derivative but the other starting material 44 is an impossible compound requiring NH2 and SH groups to be cis substituted on an alkene. Neither of these functional groups (primary enamine or thioenol) is stable and control of the geometry would also be impossible. The thiol 44 is also the thioenol of an a-amino thioketone 45 these are equally unknown. 

Treatment of enamines of type (284) with sulfur and cyanamide at room temperature in ethanol produces a range of 2-aminothiazoles (287) in 30-70% yield. Initial formation of an a-aminoenethiol intermediate (285a), which is a tautomer of an a -amino thioketone (285b), is probably followed by addition of cyanamide, yielding (286). Elimination of amine finally produces the observed thiazole (287 Scheme 202) (70JPR776). 

There is almost no restriction in the choice of an appropriate electrophile in the Knoevenagel reaction. Aldehydes, ketones, thioketones, imines, enamines, acetals and orthoesters have been used. With less reactive methylene groups, however, drastic reaction conditions may be necessary. Steric effects have a significant influence on the rate and unexpected compounds are often obtained as a result of secondary reactions. Reaction of 1,3-dicarbonyl compounds with carbon disulfide followed by dialkylation with an alkyl halide give diacylketene-S,5-acetals (159). However, even with highly acidic dicarbonyl com-... 

Smutny. The t-butyl ester was used in order to achieve hydrolysis of (30), which required reaction with trifluoroacetic acid at 0 °C for 4—5 h. Treatment of (30) with warm trifluoroacetic acid for 10 min yielded (31). The reaction of (29) with ethyl a-chloroacetate gave (32). A-Phenyl phenylpropynthioamide (33) reacts in a similar manner with active bromomethylene derivatives, such as bromo-acetonitrile, bromonitromethane, and /j-nitrobenzyl bromide, in the presence of triethylamine to give the thiophen (33a). Instead of enamine thioesters such as (29), 2-aminovinyl thioketones (34) react with a-bromo-ketones in the presence of triethylamine to give 2-acyl-thiophens (35). By the ion-pair extraction method, tetrabutylammonium salts of acetylacetone were allowed to react with carbon disulphide to give (36), which upon reaction with chloroacetone gave a 45% yield of the thiol (37), in addition to a thieno[2,3-A]thiophen derivative. ... 

Without additional reagents Thioketones from enamines... 

---