Organocatalytic oxidation. Asymmetric epoxidation of olefins catalyzed by chiral ketones and iminium salts

Metalloporphyrin-based oxidation systems: from biomimetic reactions to application in organic synthesis

The oxidation of organic substrates catalyzed by metalloporphyrins constitutes a major class of biomimetic oxidation reactions used in modern synthetic chemistry. Ruthenium porphyrins are among the most extensively studied metalloporphyrin oxidation catalysts. This article provides a brief outline of the metalloporphyrin-based oxidation systems and is focused on the oxidation reactions catalyzed by ruthenium porphyrins performed in the author's laboratory. A series of ruthenium porphyrin catalysts, including those immobilized onto insoluble supports and covalently attached to soluble supports, promote the oxidation of a wide variety of organic substrates such as styrenes, cycloalkenes, alpha,beta-unsaturated ketones, steroids, benzylic hydrocarbons and arenes with 2,6-dichloropyridine-N-oxide or air in up to >99% yields, with high regio-, chemo- and/or stereoselectivity, and with product turnovers of up to 3.0x10(4), demonstrating the potential application of ruthenium porphyrin-based oxidation systems in organic syntheses.

A diacetate ketone-catalyzed asymmetric epoxidation of olefins

A fructose-derived diacetate ketone has been shown to be an effective catalyst for asymmetric epoxidation. High ee values have been obtained for a variety of trans and trisubstituted olefins including electron-deficient alpha,beta-unsaturated esters as well as certain cis olefins.

Synthesis of epoxides by palladium-catalyzed reactions of tertiary allyl alcohols with aryl or alkenyl halides

A novel synthetic method for the preparation of tri- or tetrasubstituted epoxides is reported. Treatment of readily available tertiary allyl alcohol with aryl or alkenyl halide under palladium catalysis resulted in arylative cyclization to form the epoxide. The reaction includes intramolecular C-O bond and intermolecular C-C bond construction.

Epoxide-opening cascades in the synthesis of polycyclic polyether natural products

The structural features of polycyclic polyether natural products can, in some cases, be traced to their biosynthetic origin. However in case that are less well understood, only biosynthetic pathways that feature dramatic, yet speculative, epoxide-opening cascades are proposed. We summarize how such epoxide-opening cascade reactions have been used in the synthesis of polycyclic polyethers (see scheme) and related natural products.The group of polycyclic polyether natural products is of special interest owing to the fascinating structure and biological effects displayed by its members. The latter includes potentially therapeutic antibiotic, antifungal, and anticancer properties, and extreme lethality. The polycyclic structural features of this class of compounds can, in some cases, be traced to their biosynthetic origin, but in others that are less well understood, only to proposed biosynthetic pathways that feature dramatic, yet speculative, epoxide-opening cascades. In this review we summarize how such epoxide-opening cascade reactions have been used in the synthesis of polycyclic polyethers and related natural products.

Chiral ketone and iminium catalysts for olefin epoxidation

Organo-catalyzed asymmetric epoxidation has received much attention in the past 30 years and significant progress has been made for various types of olefins. This review will cover the advancement made in the field of chiral ketone and chiral iminium salt-catalyzed epoxidations.

Asymmetric epoxidation of 1,1-disubstituted terminal olefins by chiral dioxirane via a planar-like transition state

Various 1,1-disubstituted terminal olefins have been investigated for asymmetric epoxidation using chiral ketone catalysts. Up to 88% ee has been achieved with a lactam ketone, and a planar transition state is likely to be a major reaction pathway.