Tetrahedron p. 1313 - 1324 (1984)
Update date:2022-08-05
Topics: Thiols Racemization α-Alkylation Carboxylic Acids Tertiary alcohols
Seebach, Dieter
Naef, Reto
Calderari, Giorgio
α-Hydroxy- and α-mercapto-carboxylic acids are condensed with pivalaldehyde to give 2-t-butyl-5-substituted-1,3-dioxolanones or 1,3-oxathiolanones (2); the predominate cis-isomers are separeted by crystallization.The cis-disubstituted heterocycles 2 derived from lactic, mandelic and malic acid funish, after deprotonation with LDA, reaction with electrophiles such as alkyl halides, aldehydes and ketones, and hydrolysis α-branched α-hydroxy-carboxylic acids (3, 6, 8, 9, 10).These result from an overall substitution of the proton in the α-CO position with retention of configuration.The optically active carboxylic acids are α-alkylated without racemization and without employment of a chiral auxiliary ("self-reproduction of chirality", Scheme 1).The diastereoselectivities (ds) are generally >95percent (Table 1, 2, and 20-25).
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