Some Typical Advances in the Synthetic Applications of Allenes

Allenes are the simplest class of cumulenes, with two contiguous CC bonds, and show unique physical and chemical properties. These features make allenes particularly attractive in modern organic chemistry. In this Review, attention is paid to the advances made in catalytic asymmetric synthesis and natural product syntheses based on well-established reactions of allenes, such as propargylation, addition, cycloaddition, cycloisomerization, cyclization, etc., with or without catalysts. Their versatile reactivity, substituent-loading ability, axial to center chirality transfer, and controllable selectivity allow access to target molecules by unique and efficient approaches. The main topics in this Review are presented with selected examples from 2003 to 2011.

Allenes in Catalytic Asymmetric Synthesis and Natural Product Syntheses

Allene in katalytischer asymmetrischer Synthese und Naturstoffsynthese

Deoxy-sugars often play a critical role in modulating the potency of many bioactive natural products. Accordingly, there has been sustained interest in methods for their synthesis over the past several decades. The focus of much of this work has been on developing new glycosylation reactions that permit the mild and selective construction of deoxyglycosides. This Review covers classical approaches to deoxyglycoside synthesis, as well as more recently developed chemistry that aims to control the selectivity of the reaction through rational design of the promoter. Where relevant, the application of this chemistry to natural product synthesis will also be described.

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Methods for 2-Deoxyglycoside Synthesis.

Catalytic glycosylation has been a central reaction in carbohydrate chemistry since its introduction by Fischer 125 years ago, but it is only in the past three to four decades that catalytic methods for synthesizing oligosaccharides have appeared. Despite the development of numerous elegant and ingenious catalytic glycosylation methods, only a few are in general use. This review covers all methods of catalytic glycosylation with the focus on the development and application in oligosaccharide synthesis and provide an overview of the scope and limitations of these. The review also includes relevant mechanistic studies of catalytic glycosylations. The future of catalytic glycosylation chemistry is discussed, including specific, upcoming methods and possible directions for the field of research in general.

Catalytic Glycosylations in Oligosaccharide Synthesis

Stereoselective synthesis of 2-deoxy-β-glycosides from glycal precursors. 1. Stereochemistry of the reactions of d-glucal derivatives with phenylsulfenyl chloride and phenylselenenyl chloride

A number of simple allenes have been converted cleanly to the corresponding 1,4-dioxaspiro [2.2] pentanes in good yields by oxidation with dimethyldioxirane. Mono- and trisubstituted allenes give the anti diastereomers with good stereoselectivity, whereas 1,3-disubstituted allenes show only a slight preference for the anti,anti isomers, unless steric effects are extreme. Stereochemical assignments are based on steric considerations and a consistent set of NMR characteristics that permit structural attributions

1,4-Dioxaspiro[2.2]pentanes. Synthesis, spectroscopic properties, and reactions with nucleophiles

Stereoselective synthesis of 2-deoxy-β-glycosides from glycal precursors. 2. Stereochemistry of glycosidation reactions of 2-thiophenyl- and 2-selenophenyl-α-d-gluco-pyranosyl donors

Syntheses of functionalized C-D-E trisaccharide precusors of olivomycin A are reported. A stereoselective C-D β-glycosidation was accomplished by employing 2-deoxy-2-(phenylthio)-α-glucotrichloroacetimidate. The α-D-E glycosidic linkage was introduced by using 2-deoxy-2-iodo-α-glycosyl acetate donor as the glycosyl agent

Synthesis of C-D-E trisaccharide precursors of olivomycin A.

Highly stereoselective synthesis of α-L-olivomycosides via trimethylsilyl triflate mediated glycosidations of 1-O-acetyl-4-O-isobutyryl-2,6-dideoxy-2-iodo-3-C-methyl-α-L-mannopyranose

David P. Sebesta

Papers

Stereoselective synthesis of 2-deoxy-β-glycosides from glycal precursors. 1. Stereochemistry of the reactions of d-glucal derivatives with phenylsulfenyl chloride and phenylselenenyl chloride

1,4-Dioxaspiro[2.2]pentanes. Synthesis, spectroscopic properties, and reactions with nucleophiles

Stereoselective synthesis of 2-deoxy-β-glycosides from glycal precursors. 2. Stereochemistry of glycosidation reactions of 2-thiophenyl- and 2-selenophenyl-α-d-gluco-pyranosyl donors

Synthesis of C-D-E trisaccharide precursors of olivomycin A.

Highly stereoselective synthesis of α-L-olivomycosides via trimethylsilyl triflate mediated glycosidations of 1-O-acetyl-4-O-isobutyryl-2,6-dideoxy-2-iodo-3-C-methyl-α-L-mannopyranose