Chapter 13. Synthetic methods

Abstract

The pace of advance in organic synthesis makes it impossible to include more than a selection of recent methods in this Report. A number of important topics, for example oxidation and reduction, have been omitted (but not forgotten), and it is hoped that it may be possible to include some of these in next year's Report. AlcoholsAn extremely simple, convenient, and selective method for acetylating primary alcohols in the presence of secondary ones has been reported,' and has been applied in the carbohydrate series.* Primary hydroxyalkylphenols are thus converted into acetoxyalkylphenols and primary aromatic amines into the corresponding acetamides. t-Butyldimethylsilyl, tri-isopropylsilyl, and octadecyldimethylsilyl triflates are useful reagents for silylation of hindered alcohols which react sluggishly with the usual silylating agent^.^ 1,2-and 1,3-diols are conveniently protected by conversion into their di-t-butylsilylene derivatives by reaction with di-t-butyldichlorosilane. The protecting group is easily removed by treatment with pyridinium hydr~fluoride.~The de-oxygenation of secondary alcohols by radical reduction of thiocarbonyl esters has been shown to be a general reaction of value in the synthesis and modification of natural products.' By appropriate modification of experimental conditions the reaction has now been extended to primary alcohols.6 A modified Barton procedure was used to convert ribonucleosides into 2'-deoxyn~cleosides.~ Methods for the inversion of secondary alcohols are valuable in synthesis. Caesium carboxylates in dimethyl formamide are good nucleophiles and are useful for the introduction of hydroxy-substituents by SN2 nucleophilic substitution. In practice the best results were obtained with the propionate. Mesylates of several secondary alcohols were cleanly converted into the propionates of the inverted alcohol in high yield in warm dimethyl formamide. The inversion of (S)-2-octanol,