Β-enamino Acid Derivatives Research Articles

An efficient synthesis of uracil derivatives from 2-alkyl-Δ 2-oxazolines and nitriles

An efficient and convenient synthesis of new fluorinated and non-fluorinated uracils is described herein. The condensation of nitriles with enolates generated from 2-alkyl-Δ 2-oxazolines (I) affords fluorinated β-enamino acid derivatives, which react with triphosgene to give an isomeric mixture of oxazolopyrimidinones. These can then be easily transformed into a single C-6 pyrimidindione derivative through reaction with a suitable nucleophile.

Asymmetric synthesis of homoproline derivatives via Rh(I)-catalyzed hydrogenation using chiral bisphosphines as ligands

It has been demonstrated for the first time that Rh(I)-catalyzed asymmetric hydrogenation of cyclic β-enamino acid derivatives 1 using chiral bisphosphines could be a highly efficient synthetic method for optically active homoproline derivatives. The enantioselectivity and conversion yield were largely dependent upon the chiral ligand. Using the Me-BDPMI forming a seven-membered metal chelate, the N-acetylated β-enamino acid methyl ester 1a was hydrogenated to give optically active homoproline derivative 2a with 100% conversion and 96% ee.

Novel strategy for the synthesis of fluorinated β-amino acid derivatives from Δ 2-oxazolines

Racemic and chiral non-racemic β-fluoroalkyl-β-amino acid derivatives have been prepared in two steps starting from 2-alkyl-Δ 2-oxazolines and fluorinated imidoyl chlorides. Subsequent chemoselective reduction of the C-masked β-enamino acid derivatives initially formed provided the target β-amino acids. The process takes place with total chemoselectivity, high yields and satisfactory diastereoselectivity.

A new and expeditious strategy for the synthesis of β-amino acids from Δ 2-oxazolines

A new, mild two-step synthesis of racemic β-amino acids starting from 2-alkyl-Δ 2-oxazolines is described. The process implies the initial formation of masked N-substituted or N-unsubstituted β-enamino acid derivatives followed by chemoselective reduction of the enamino moiety. The process takes place with high yields, total chemoselectivity and moderate diastereoselectivity.

Synthesis and C-alkylation of C-protected β-enamino acid derivatives from oxa- thia- and imidazolines

Various heterocycles 3a-h can be readily metallated and condensed with a variety of organic nitriles to afford C-protected β-enamino acid derivatives 1 (or 2). Procedures for alkylation of compounds 1 to obtain 2 as well as a “one-pot” preparation of 2 from 3 are also described.

A new and mild synthesis of β-amino acids from masked β-enamino acid derivatives

A new method of synthesis of racemic β-amino acids 6 by reduction of masked N-substituted and N-unsubstituted β-enamino acid derivatives 4 via C-protected β-amino acids 5 is described. The process occurs with high yields, total chemoselectivity and moderate diastereoselectivity. Readily available starting materials, inexpensive reagents and mild conditions are used to furnish derivatives 5 and 6.

Synthesis and Reactivity of New β-Enamino Acid Derivatives: A Simple and General Approach to β-Enamino Esters and Thioesters

A new strategy has been developed for the synthesis of several β-enamino acid derivatives. N,N‘-Carbonyldiimidazole has been used as C-acylating agent of methyl ketimines, providing a direct and simple route to new β-enamino carbonyl imidazole derivatives 2. These derivatives 2 were cleanly and efficiently transformed into β-enamino esters 4 (X = O) and thioesters 4 (X = S) by reaction with a great variety of alcohols and thiols, including tertiary ones. Alternative and complementary routes to compounds 4 were also investigated. In addition, β-keto esters 6 have been obtained by mild acid hydrolysis of β-enamino esters 4.

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

Reaction of fluorinated imidoyl chlorides 1 with lithium ester enolates 2 gave N-substituted γ-fluorinated β-enamino and/or β-imino esters 4 in good to excellent yields. β-Enamino esters were obtained exclusively as Z isomers. © 1997 Published by Elsevier Science Ltd.

An Efficient and Simple Entry to N-Substituted beta-Enamino Acid Derivatives from 2-Alkyl-2-oxazolines and 2-Alkyl-2-thiazolines.

Reaction of azaenolates of 2-alkyl-oxa(thia)zolines 6 with imidoyl chlorides 7 as electrophiles to furnish masked N-substituted beta-enamino acid derivatives 1-2 in 70-90% yield is described. Alternative routes are discussed. Compounds 1-2 generally appear in one tautomeric form, imino or enamino, depending on the nature of the imidoyl chloride. The configuration of the enamino moiety (Z) and the conformation (s-cis) of compounds 1-2 obtained were established by an NMR study and unequivocally set by nuclear Overhauser effect difference experiments. An X-ray structure of compound 1e is also reported, showing a strong intramolecular NH.N hydrogen bond. Ab initio calculations (HF/3-21G and HF/3-21+G) have been carried out on several representative examples (1e, 1p, and 1l) in an attempt to support and provide the correct geometry of these derivatives. Structural considerations among the possible isomers of compounds 1 are discussed. From these studies it was concluded that the theoretical calculations agree with the experimental results. In addition, a very simple one-pot procedure for the preparation of masked N-substituted alpha-alkylated beta-enamino acid derivatives 2 from 6, 7, and different alkyl halides (R(3)Y) is described.

A new method for the regioselective synthesis of β-enamino acid derivatives

A mild, simple and efficient route to β-enamino imidazole carbonilic derivatives 3 by reaction of ketimines with N,N′-carbonyl diimidazole in the presence of boron triflouride as catalyst has been developed. The conversion of 3 to esters has also been explored.