Current Organic Chemistry - Volume 13, Issue 6, 2009

The aim of this review is to emphasize the value of unsaturated carbohydrate derivatives as a ground floor for useful synthetic transformations. In this context, we highlight the rich chemistry of Δ2,3 unsaturated pyranosides by way of the different transformations carried out in the Fraser-Reid laboratories during the past four decades. These transformations have all led to the synthesis of natural products. Cyclopropanated derivatives were used in an enantiodivergent approach to chrysantemic acids. The former, also paved the way to a stereoselective synthesis of sucrose. An investigation on the aldehydic nature of tri-O-acetyl glucal triggered an approach to trichothecenes. The allylic hydroxyl of unsaturated sugars was used fulcrum to direct the entry of the cis nitrogen in synthetic approaches to ristosamine and daunosamine. The discovery of the photochemically induced addition of alcohols and aldehydes to unsaturated enones was employed in an unequivocal synthesis of pillarose, the sugar component of antibiotic pillaromycin A. Unsaturated enones also proved to be precious synthetic intermediates in Diels-Alder reactions: an intermolecular Diels-Alder transformation was used in the synthesis of actinobolin, whereas its intramolecular version was employed in the synthesis of an advanced intermediate of forskolin. The concatenation of unsaturated sugars was key in the development of the “pyranosidic homologation” concept that led to the synthesis of the ansa chain of streptovaricin A. Finally, radical cyclization and serial radical reactions on unsaturated sugars were used in the synthesis of cyclophellitol and reserpine.

The recent developments on the synthetic applications of polyunsaturated silanes are reviewed. Different substrates will be considered, ranging from silylated conjugated dienes, enynes, polyenynes, diynes and polyynes. All these compounds represent versatile building blocks in the organic synthesis, as demonstred from the numerous applications, regarding especially the stereoselective synthesis of natural products with a conjugated polyunsaturated structure.

This review focused on recent advances in free radical chemistry in water or aqueous media. Highlights in the progress have been made in the last decade to “tame” the reactive free radical species in aqueous phase reactions. Recent advances in several classes of widely useful free radical reactions in water have expanded the versatility and flexibility of the carbon-carbon bond formation. The review will also explore the recent advances in performing stereo-selective free radical reactions in an aqueous medium and its application in synthesis of natural and unnatural amino acids, preparation of novel materials and solid support chemistry. Some practical hints for help design high yielding free radical reactions in aqueous medium are also presented.

This review describes the formation of five- and six-membered heterocyclic rings in various compounds by radical cyclisation and covers the recent literature mostly of 2007.

Daphniphyllum alkaloids are a growing group of secondary metabolites of great structural diversity, with complex polycyclic skeletons from Daphniphyllum plants. A large number of new Daphniphyllum alkaloids with novel frameworks have been isolated from Daphniphyllum species in the past decade. These unusual structural characteristics will attract the attention of scientists in the fields of organic synthesis, bioactivity evaluation and biosynthetic studies. This review lists all the Daphniphyllum alkaloids as well as their biosynthesis, bioactivity and synthesis reported by the end of first half of 2008.