Herpin, Timothée Felix; (1995) Some new reactions of anomeric difluoromethylene carbohydrate derivatives. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is divided into three chapters. Chapter one presents a review of the preparation of gem-difluoromethylene substituted natural product analogues by the fluorinated synthon approach. The reactivity and versatility of various synthons are discussed with particular reference to the disconnection of complex gem-difluorinated molecules. Chapter Two describes some new radical and ionic reactions for the conversion of exocyclic carbohydrate gem-difluoroenol ethers into fluorinated natural product analogues. The first section outlines the preparation of carbohydrate gem-difluoroenol ethers from the corresponding lactones by a Wittig-type reaction. The following section describes their conversion into difluoroglycophosphonates by reaction with diethyl phosphite or diethyl (phenylselenyl)phosphonate, a new reagent for the efficient generation of phosphonyl radicals under mild conditions. The reaction of gem-difluoroenol ethers with nucleophilic radicals is reported as a general route to difluoromethylene bridged disaccharides and glycopeptides. The procedures involve the addition of radicals generated from 6-iodopyranoside or bromo-β-alanine derivatives to these ethers using tin mediated conditions. The preparation of a new and versatile amino acid synthon for radical reactions is also described. The reaction of electrophilic carbon centred radicals with carbohydrate gem-difluoroenol ethers has been envisaged, and applied to the preparation of spirofused difluorocarbocycles under atom transfer conditions. In the final section, the conversion of carbohydrate gem-difluoroenol ethers into gem-difluorocyclitols is explored. Chapter Three provides a formal description of the experimental results and procedures.

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