Total synthesis of (+)-monomorine I via nitrone cycloaddition route

The synthesis and biological evaluation of 1-C-alkyl-L-arabinoiminofuranoses, a novel class of α-glucosidase inhibitors

The asymmetric synthesis of 1-C-alkyl-l-arabinoiminofuranoses 1 was achieved by asymmetric allylic alkylation (AAA), ring closing metathesis (RCM), and Negishi cross coupling as key reactions. Some of the prepared compounds showed potent inhibitory activities towards intestinal maltase, with IC(50) values comparable to those of commercial drugs such as acarbose, voglibose, and miglitol, which are used in the treatment of type 2 diabetes. Among them, the inhibitory activity (IC(50)=0.032μM) towards intestinal sucrase of 1c was quite strong compared to the above commercial drugs.

Asymmetric 1,3-dipolar cycloadditions of acrylamides

This critical review, which is relevant to researchers in synthetic organic chemistry, focuses on asymmetric 1,3-dipolar cycloadditions with acrylamides. The use of chiral acrylamides as dipolarophiles leads to high levels of stereocontrol, due to conformational constraint in the acrylamides. Employment of chiral tertiary acrylamides containing nitrogen heterocycles is particularly effective in controlling the stereoselectivity. Following a general overview of 1,3-dipolar cycloadditions, the main body of the review focuses on asymmetric 1,3-dipolar cycloadditions of acrylamides with nitrile oxides, nitrones, diazoalkanes and azomethine ylides, with particular emphasis on the rationale for the observed stereocontrol (215 references).

Catalyst-directed diastereoselectivity in hydrogenative couplings of acetylene to alpha-chiral aldehydes: formal synthesis of all eight L-hexoses

Hydrogenative coupling of acetylene to alpha-chiral aldehydes 1a-4a using enantiomeric rhodium catalysts ligated by (S)-MeO-BIPHEP and (R)-MeO-BIPHEP delivers the diastereomeric products of carbonyl-(Z)-butadienylation 1b-4b and 1c-4c, respectively, with good to excellent levels of catalyst directed diastereofacial selectivity. Diastereomeric L-glyceraldehyde acetonide adducts 1b and 1c were converted to the four isomeric enoates 6b, 8b, 6c, and 8c, representing a formal synthesis of all eight L-hexoses.

Improvement of TADDOLate-TiCl(2)-Catalyzed 1,3-Dipolar Nitrone Cycloaddition Reactions by Substitution of the Oxazolidinone Auxiliary of the Alkene with Succinimide

A significant improvement of metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions of acyclic nitrones with alpha,beta-unsaturated carbonyl compounds is described using succinimide as a new auxiliary for the alpha,beta-unsaturated carbonyl moiety. In the absence of a catalyst, N-crotonoylsuccinimide reacts with C,N-diphenylnitrone to give the endo-isoxazolidine, whereas in the presence of 10 mol % TiCl(2)(i-PrO)(2) the exo-product is obtained. Four different TiCl(2)-TADDOLate complexes have been tested as catalysts for the 1,3-dipolar cycloaddition reactions, and the most successful catalyst was applied (5 mol %) in a series of reactions between two different alkenoylsuccinimides and three different nitrones. The crude products containing an N-acylsuccinimide moiety were converted directly into the corresponding carboxamides upon treatment with hydrazine. The 1,3-dipolar cycloaddition reactions proceed with a high degree of exo-selectivity, often >90% de, which is an improvement compared with previous experiments performed using the oxazolidinone auxiliary for the alkenoyl moiety. Furthermore, the enantioselectivities are also improved compared with previous work, and ee up to 73% is obtained, which is the highest ee found for these metal-catalyzed exo-selective 1,3-dipolar cycloaddition reactions. The ee can be improved to >90% by recrystallization. The absolute structure of the 1,3-dipolar cycloaddition adduct is determined on the basis of the X-ray crystal structure of a compound with a known configuration. On the basis of this knowledge of the absolute structure of the product the mechanism of the reaction is briefly discussed.