Enamines with isothiocyanates

Reactions of enamines with isocyanates (568) and isothiocyanates (569) in the presence of sulfur gave l,3-thiazolidine-2-ones and l,3-thiazolidine-2-thiones. 

Substituted 2-pyridones were obtained from enamines with appropriate functional groups. Phenyl isocyanates and phenyl isothiocyanates... 

The synthesis of the pyrimidine ring represents a well-studied group of heterocyclization reactions based on enamines. One of the important approaches involves the reaction of enamines with assorted isocyanates and isothiocyanates. Thus, a reaction of enaminonitriles with benzyl isocyanate or phenyl isocyanate gives C- and N-adducts (190a and 190b, respectively) or their mixtures, which are transformed in a single step into 4-pyrimidinone (191) and 2-pyrimidinone (192) derivatives (94JHC329). The... 

Reactions of enamines with monoimines of o-quinones afford polycylic compounds 228 with an oxazine ring (86MI2).Trifluoroacetylation of enamines with trifluoroacetic acid takes place in the /3-position of the enamine. Ketones (229) thus formed in an acidic medium afford fused 1,3-oxazines (230) (82JOC3339). Treatment of amines with silyl isothiocyanate gives not only pyrimidine derivatives but also l,3-oxazine-4-thiones (231) (81CCC2696). 

Thioamides are suitable intermediates for the preparation of amidines, thiazoles, and thiophenes. Thioamides have mainly been prepared on insoluble supports by C-acylation of enamines or C,H-acidic compounds with isothiocyanates (Entries 1-3,... 

Enamine 17 reacts smoothly at 20°C with isothiocyanates to furnish 4-trifluoromethyl thiouracils 15 (Scheme 52, ref. 44). 

The interaction of enamines with sulphur in conjunction with carbon disulphide, isocyanates, or isothiocyanates results in the production of sulphur-containing heterocyclics. Cyanamide has now been shown to participate in this reaction. Treatment of enamines of type (24) with sulphur and cyanamide at room temperature in ethanol produces a range of 2-aminothiazoles (27) in 30—70% yield no catalyst is required. Initial formation of the thiolated intermediate (25) is probably followed by addition of cyanamide, yielding (26) elimination of amine finally produces the observed thiazoles (27). Since AW-dialkylcyanamides do not undergo this reaction, cyanamide may react as the tautomeric carbodi-imide. An actual example of the reaction employing the enamine derived from cyclohexanone and morpholine is also shown [(28) - (29)]. ... 

The reaction of isothiocyanates with linear and cyclic olefins, activated with dialky-lamino substituents, is generally exothermic, with only short heating in an inert solvent being necessary to produce high yields of the linear 1 1 adducts 29. The reaction proceeds via a [2+2] cycloaddition and subsequent rearrangement to give the final product. Several examples of linear products derived from enamines and isothiocyanates are listed in Table 3.13. 

The reaction of the morpholine enamine of cyclohexanone with phenyl isothiocyanate led only to the tetrasubstituted isomer of the monoadduct (54), which failed to add any more of the phenyl isothiocyanate. The formation of only the tetrasubstituted isomer has been attributed by Hunig et al. (37) to the stronger conjugation of the C=S group with the enamine double bond than that of the C=0 group in the enamine (49). 

The reaction of the enamines of cyclic ketones with alkyl isocyanates, acyl isocyanates, phenyl isothiocyanates, and acyl isothiocyanates has also been reported 112). The products are the corresponding carboxamides. The products from the isothiocyanates have been utilized as intermediates in the preparation of various heterocyclic compounds 113). 

Schiff s bases also underwent C or N acylation with isocyanates (698) and isothiocyanates (698,701). Further studies provided 2 1 and 2 2 reaction products of arylisothiocyanates and enamines (702) and polymers derived from enamines and bisisocyanates (703). 

The addition of isocyanides and azide to aldehyde-derived enamines has led to tetrazoles (533,536). On the other hand the vinylogous amide of acetoacetic ester and related compounds reacted with aldehydes, isocyanides and acids to give a-acylaminoamides (534). Iminopyrrolidones and imino-thiopyrrolidones were obtained from the addition of cyclohexylisocyanide and isocyanates or isothiocyanates to enamines (535). An interesting method for the formation of organophosphorus compounds is found in the reactions of imonium salts with dialkylphosphites (536). 

Fairly complex approaches have been used to construct thiazoles substituted with an enamine group. The cyclocondensation of l-tosyl-2,2-dichloroethenyl isothiocyanate 21 with various enamines such as 22 affords enamino substituted thiazoles such as 23 in high yields <00MI109>. 

In contrast to 4-alkyl-5-sulfonylimino-A -l,2,3,4-thiatriazolines (58) (Section 4.19.5.1.2), 4-alkyl-5-alkylimino-A -l,2,3,4-thiatriazolines (50) react with immediate nitrogen evolution when added to electron-rich alkenes or to heterocumulenes such as enamines, carbodiimides, isocyanates, isothiocyanates, or styrene. Reaction kinetics for certain of this type of system show that they undergo bimolecular processes as described below. 

Cycloaddition reactions of sulfonyl isothiocyanate 76 and, -disubsti-tuted enamines were studied by Schaumann et The mechanism of cycloaddition is postulated to consist of two steps, originating with the formation of the zwitterionic adduct 77. 

The course of this reaction could be explained by nucleophilic attack of the isothiocyanato group on C-5 (hard site) of enamine 61, with the formation of 199 by way of intermediate 198. However, this occurs only in N,N-dimethylformamide or acetonitrile solution. The formation of the additional products 2-glycosyliminothiazolo[4,5-d]pyrimidine-4,6-dione (201) by way of intermediate 200, by attack of the isothiocyanato group on the 6-amino group (soft site), was observed when the reaction was performed in oxolane solution. On the other hand, treatment of isothiocyanates 2, 30,... 

Perfluoro-2-methyl-2-penten-3-yl isothiocyanate, which was prepared from perfluoro-2-methyl-2-pentene and KSCN in benzonitrile in high yield by direct substitution of fluorine, is a stable and versatile educt for heterocyclic synthesis. This a,p-unsaturated isothiocyanate reacted with enamines, such as 1-methylindole and 2-methyl-1-morpholino-l-propene, to yield 2-(l-methylindol-3-yl)-perfluro-4,5-dihydro-5,5-dimethyl-4-ethylidene-l,3-thiazole and its analogue in fair yield. [95H1015]... 

The schemes presented below also illustrate the synthesis of various amides of substituted quinoline-and quinolonecarboxylic acids 212-214 by the reaction of isatins 7, 9, 54, and 180 with amides 215 [179], acylated amino acids 216 and isothiocyanates [182], and enamines 217 [183],... 

Carbonyl compounds and other dipolarophiles containing heteroatoms react with miinch-nones. Thus benzaldehyde forms the betaine (245) which suffers ring-cleavage to yield the enamine (246 equation 65). Thiocarbonyl compounds and nitrosobenzene behave in an analogous manner. The action of dipolarophiles containing cumulative double bonds results in the formation of new mesoionic systems. Thus carbon disulfide and phenyl isothiocyanate afford a zwitterionic thiazole and imidazole, respectively (Scheme 25). 

In the absence of dipolarophiles the intermediate loses sulfur to give the carbodiimide however, the intermediate may be trapped with a number of alkenes, heterocumulenes and other reagents such as ynamines, ketenes, isocyanates, isothiocyanates, carbodiimides, ketenimines, sulfonylimines, imines, nitriles, thiocarbonyl compounds, Wittig reagents and the already mentioned enamines (80AG277). Contemporary knowledge of the chemistry of these sulfonyliminothiatriazolines is mainly due to the meticulous work of L abbe and his coworkers (80AG277). 

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