N-Substituted β-Enamino Acid Derivatives: A New Approach to Fluorinated β-Enamino Esters

VCl3 Catalysed Efficient Synthesis of β-enamine Esters and Ketones from β-keto Esters

VCl3 is a useful and efficient catalyst for the synthesis of β-enamine esters and ketones from β-keto esters with primary amines.

Nucleophilic substitution reactions of N-alkoxyimidoyl fluorides by carbon nucleophiles

Nucleophilic substitutions of N-alkoxybenzoimidoyl fluorides [p-ClArC(F)=NOR; R = CH3, i-Pr] by enolate-type ions have been performed to produce compounds that can exist in two tautomeric forms: the imine form{p-ClArC(Y)=NOR [Y = CH(CN)2, CH(CN)(CO2Et), CH(CO2Et)2]}or the enamine form {p-ClArC(NHOR)=C(R1)(R2) [R1, R2 = CN, CO2Et]}. These compounds display varying ratios of imine–enamine tautomerizm in chloroform: the diester compound exists almost solely in the imine form, the dicyano compound exists solely in the enamine form, and the cyano-ester compound exists in both tautomeric forms. Comparison of the imine–enamine equilibrium in chloroform of the cyano-ester compound to an analogue where the p-ClAr group has been replaced by a methyl group reveals that the aromatic ring has a significant effect on the imine–enamine distribution. The former exists in both the imine and enamine form, while the latter exists solely in the enamine form. Complete NMR characterization data for the enamine form of CH3C(NHOCH3)=C(CN)(CO2Et) is also reported. The acidity of p-ClArC(NHOR)=C(CN)2 is demonstrated by a high degree of dissociation of the enamine proton in DMSO. Substitution reactions of p-ClArC(F)=NOi-Pr by Grignard reagents (PhMgBr, CH3MgBr, and PhCCMgBr) have also been performed to produce single geometric isomers of p-ClArC(Ph)=NOi-Pr, p-ClArC(CCPh)=NOi-Pr, and p-ClArC(CH3)=NOi-Pr. A modified synthesis of N-alkoxyimidoyl fluorides, which prevents a competing reaction of the product with the solvent, is reported.Key words: N-alkoxyimidoyl fluoride, enolate ion substitution, Grignard substitution, imine–enamine tautomerizm, carbon acid.

C-Aminoimidoylation and C-Thiocarbamoylation of Esters, Sulfones, and Ketones

Esters, sulfones, and ketones were C-aminoimidoylated and C-thiocarbamoylated by benzotriazole-1-carboxamidines 8a-g and 1-(alkyl-or-arylthiocarbamoyl)benzotriazoles 9a-i, respectively. The present work represents the first systematic approach to these compound classes, the few previously known examples of which were obtained by diverse approaches.

Diastereoselective synthesis of S-tert-butyl-beta-(trifluoromethyl)isocysteine

Both diastereoisomers of S-tert-butyl-beta-(trifluoromethyl)isocysteine have been synthesized stereoselectively by the sequential reactions of trifluoroacetimidoyl chloride with the lithium enolate of tert-butyl alpha-tert-butylthioacetate, followed by the diastereoselective reduction of the imino group with sodium borohydride in the presence of zinc(II) or di(ethylene glycol) dimethyl ether, and finally by the deprotection of N-aryl and tert-butyl ester groups.

New Strategies for the Synthesis of Fluorinated Vinylogous Amidines and beta-Enamino Ketones

Reaction of fluorinated imidoyl chlorides 3 with ketimines 1a provides fluorinated 1,3-diimines, which were exclusively isolated as vinylogous amidine tautomers 2beta, with good yields. Fluorinated beta-enamino ketones 4 are obtained by regioselective hydrolysis of 2. Complementary methods for the synthesis of regioisomeric beta-enamino ketones 4 and 5 are also reported. These methods include the reaction of azaenolates of ketimines with fluorinated esters 6 and reactions of ketone enolates with fluorinated imidoyl chlorides 3. The behavior of these systems in hydrolysis reactions was also tested.