Carbonyl asymmetric esterification

A similar catalytic procedure for enantioselective formation of C-Br and C-Cl bonds has been reported recently by the Lectka group [83]. The concept of this a-halogenation of carbonyl compounds is tandem asymmetric halogenation and esterification (Scheme 3.28). Inexpensive acyl halides, 74, are used as starting... 

The GC separation of enantiomeric d- and L-amino acids with nonchiral phases requires their conversion to diastereomeric derivatives. The second asymmetric center in the molecule ( ) arises after esterification by optically active alcohols [2-BuOH, 2-AmOH, pinacolol, (-)-menthol, etc.] or NH2 group acylation by chiral reagents e.g., a-methoxy-a-trifiuoromethylphenylacetyl chloride [MTPAC (IV)], A-trifiuoroacetyl-L-prolyl chloride [N-TFA-L-Pro-Cl (V)], A-trifiuoroacetyl-thiazolidine-4-carbonyl chloride (VI), etc. ... 

The asymmetric syntheses of (-)-methyl kaur-16-en-19-oate and (-)-methyl trachyloban-19-oate was achieved by M. lhara and co-workers. One of the last transformations was the deoxygenation of the ketone carbonyl group of the tetracyclic intermediate, which was effected by the Wolff-Kishner reduction. Under the strongly basic conditions the ester functionality was hydrolyzed, so an esterification using diazomethane was necessary as the final step. The major deoxygenated product was (-)-methyl kaur-16-en-19-oate (59%). The minor product was identified as (-)-methyl trachyloban-19-oate (16%). 

Benzylic C-H bonds undergo oxidative esterification with TBHP in the presence of tetrabutylammonium iodide as catalyst and carboxylic acids in good to excellent yields. A free radical process has been proposed. Asymmetric epoxidation of electron-poor terminal alkenes bearing different carbonyl groups has been achieved with a cinchona thiourea/TBHP system. The corresponding epoxides, containing a quaternary stereocentre, were isolated in yields up to 98% and enantioselectivity up to 99%. A direct oxidative CDC of indole with A-aryltetrahydroisoquinolines in the 0 presence of a gold catalyst and TBHP resulted in the formation of a variety of alkylated heteroarenes (Scheme 24). ... 

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