Rearrangement chiral, reaction with

The advantages of the carbon tetrahalide-organophosphine-alcohol reaction to prepare halides are simplicity of experimental procedure good yields relatively mild, essentially neutral reaction conditions absence of allylic rearrangements. The reaction proceeds with inversion of configuration and is a useful simple device for converting optically active alcohols to chiral halides in high optical purity.12-22... 

Recently, new examples of asymmetric induction in the Pummerer reaction of chiral sulfoxides have been described. Oae and Numata (301) reported that the optically active a-cyanomethyl p-tolyl sulfoxide 275 undergoes a typical Pummerer rearrangement upon heating with excess of acetic anhydride at 120°C, to give the optically active a-acetoxy sulfide 276. The optical purity at the chiral a-carbon center in 276, determined by means of H- NMR spectroscopy using a chiral shift reagent, was 29.8%. 

Norpseudoephedrine-derived amino ether 81 was also used as a chiral coordinating agent for the enantioselective [2,3]-Wittig rearrangement. The rearrangement of propargyl ether 82 induced by n-BuLi/81 provided allenyl alcohol (5 )-83 in 62% ee (equation 45). In contrast, a similar reaction with (-)-24 provided only 9% ee of (S)-S3. 

Chiral Substrates with Other Achiral Reagents Diastereoselective Claisen Rearrangement and Wittig Reactions... 

Chiral 2,2-disubstituted cyclobutanones have been obtained by asymmetric rearrangement of chiral sulfinyl- 177,178 and sulfanylcyclopropanes.179 Using readily available cyclopropyl 4-tolyl (/ )-sulfoxide (l),180 the requisite sulfinylcyclopropanes 3 and 3 were obtained by a sequence of lithiation, reaction with carboxylic acid esters and stereoselective addition of Grignard reagents to the ketones 2 thus formed.178 The corresponding sulfanylcyclopropanes 4 and 4 resulted from a sequence of protection, reduction and deprotection.179... 

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