Introduction of Fluorine

A rearrangement similar to that described in Surprise 3 occurs when l,l-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT) is treated with anhydrous hydrogen fluoride and red mercuric oxide [7]. Intermediates assumed in this reaction are shown in the following equations. 

The intermediate II is assumed to dissociate and release chlorine anion, leaving cation III that rearranges prior to its combination with the fluoride anion present in the reaction mixture (IV and V) [7], Similar reactions are involved in the conversion of l,l-bis(p-chlorophenyl)-1,2,2,2-tetrachloroethane. 

Diethylaminosulfur trifluoride reacts with the 2-hydroxyl to form an intermediate (V) in which the neighboring benzyloxy group participates, forming a three-membered epoxide ring (VI). This is cleaved by the fluoride ion detached from the intermediate VI, and the result is a product with retention of configuration, benzyl 3-azido-4,6-0-benzylidene-2,3-dideoxy-2-fluoro-a-D-altropyranoside II. 

The intermediate VI formed from the starting material and diethylaminosulfur trifluoride undergoes an SNi reaction in an eight-membered transition state involving the azido group. The replacement occurs with 

The intermediate VII formed from the starting compound and diethyl-aminosulfur trifluoride reacts by an SN2 mechanism to yield a product with inversion of configuration on carbons 1 and 2, 2-benzyl-3-azido-4,6-0-benzylidene-3-deoxy- 3-D-allopyranosyl fluoride (IV) [8]. 

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As a result, the intervening 15 years have witnessed the development of procedures for the introduction of fluorine in practically every available position of the steroid nucleus. Moreover, fluorine-containing groups such as CF2 and CF3 have been substituted at various positions. A number of recent books and reviews deal extensively with this subject. ... 

Fluorme-containing Michael addition acceptors have been used as synthons, a portion of a molecule recognizably related to a simpler molecule, for the introduction of fluorine into the organic molecules Their reactions with enamines and ketones lead to a condensarion-cyclization process... 

Introduction of fluorinated alkyls into heterocycles 97MI33. 

Eluorination of heteroaromatic compounds and introduction of fluorine-containing substituents 96MI6. 

This discussion is separated into three sections depending on whether fluorine, or polyfluoroalkyl group, is introduced into a heterocycle or whether the heterocycle is formed from fluorinated synthons. Methods of introduction of fluorine into N-containing heterocyclic compounds have been reviewed (90CLY959). 

A. Introduction of Fluorine into a Heterocycle 1. Nucleophilic Halogen Exchange... 

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