Efficient Asymmetric Synthesis of Quaternary (E)-Vinylglycines by Deconjugative Alkylation of Dehydroamino Acids

A convergent, umpoled synthesis of 2-(1-amidoalkyl)pyridines

A convenient, one-pot, two-component synthesis of 2-(1-amidoalkyl)pyridines is reported, based upon the substitution of suitably-activated pyridine N-oxides by azlactone nucleophiles, followed by decarboxylative azlactone ring-opening. The synthesis obviates the need for precious metal catalysts to achieve a formal enolate arylation reaction, and constitutes a formally ‘umpoled’ approach to this valuable class of bioactive structures.

Direct C-H functionalization of enamides and enecarbamates by using visible-light photoredox catalysis

Direct C-H functionalization of various enamides and enecarbamates was realized through visible-light photoredox catalyzed reactions. Under the optimized conditions using [Ir(ppy)(2)(dtbbpy)PF(6)] as photocatalyst in combination with Na(2)HPO(4), enamides such as N-vinylpyrrolidinone could be easily functionalized by irradiation of the reaction mixture overnight in acetonitrile with visible light. The scope of the reaction with respect to enamide and enecarbamate substrates by using diethyl 2-bromomalonate for the alkylation reaction was explored, followed by an investigation of the scope of alkylating reagents used to react with the enamides and enecarbamates. The results indicated that reaction takes place with quite broad substrate scope, however, tertiary enamides with an internal C=C double bond in the E configuration could not be alkylated. Alkylation of N-vinyl tertiary enamides and enecarbamates gave monoalkylated products exclusively in the E configuration. Alkylation of N-vinyl secondary enamides gave doubly alkylated products. Double bond migration was observed in the reaction of electron-deficient bromides such as 3-bromoacetyl acetate with N-vinylpyrrolidinone. A mechanism is proposed for the reaction that is different from reported reactions of SOMOphiles with a nonfunctionalized C=C double bond. Further tests on the trifluoromethylation and arylation of enamides and enecarbamates under similar conditions showed that the reactions could serve as a mild, practical, and environmentally friendly approach to various functionalized enamides and enecarbamates.

Lewis acid promoted highly diastereoselective Petasis Borono-Mannich reaction: efficient synthesis of optically active β,γ-unsaturated α-amino acids

An efficient and straightforward method for the preparation of highly enantiomerically enriched β,γ-unsaturated α-amino acid derivatives by a Lewis acid promoted diastereoselective Petasis reaction of vinylboronic acid, N-tert-butanesulfinamide, and glyoxylic acid has been developed. The synthetic utilities of the approach were demonstrated by the rapid and convenient construction of challenging cyclopenta[c]proline derivatives.

Asymmetric synthesis of beta,gamma-unsaturated alpha-amino acids via efficient kinetic resolution with cinchona alkaloids

The beta,gamma-unsaturated amino acids are versatile chiral building blocks and biologically interesting compounds. The asymmetric synthesis of beta,gamma-unsaturated amino acids presents a challenging task as these compounds are labile toward racemization as well as the undesirable double bond isomerization. An efficient, general and mild kinetic resolution with readily accessible and fully recyclable cinchona alkaloid catalysts has been developed to provide a reliably useful approach toward optically active beta,gamma-unsaturated amino acids.

Enamides: valuable organic substrates

Enamides display a fine balance of stability and reactivity, which is now leading to their increasing use in organic synthesis. Enamides offer multiple opportunities for the inclusion of nitrogen based functionality into organic systems. Recent examples of these compounds as substrates are discussed in this article.