A-Methylcarboxylic acids

Tiglic acid to a-methylcarboxylic acid Ru(OCOCH3)2(H8-BINAP)... 

The 5-ketone (16), which is readily obtainable from 5-mandelic acid, is converted into the /8-hydroxy-a-methylcarboxylic acid (17) in high enantiomeric and diastereoisomeric excess by the aldol condensation of the corresponding dicyclopentylborinyl enolate (Scheme 13). This simple yet highly effective idea, and its extensions, provides the cornerstone of one of the major achievements reported this year, the total synthesis of 6-deoxyerythronolide B (see Section 4). 

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