By Gary M. Coppola

Consciousness artificial chemist! Chiral alpha-hydroxy acids to be had from nature's chiral pool function beginning fabrics in a large choice of enantioselective conversions resulting in commercially vital items. This monograph, a stimulating resource of rules and a necessary reference paintings for learn chemists, specializes in the well known lactic, mandelic, malic, and tartaric acids. Well-chosen examples convey how chiral facilities inherent in those easy compounds can be utilized to manage the creation of extra stereogenic facilities. Readers can without delay observe new alterations of their personal paintings given that response stipulations are given in convenient tables.

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1 lists the protective groups mentioned in this section and some standard methods for their removal. 1. 1 Acetyl o O CH3 (S)-2-(Acetyloxy)propanoic Acid L-2-Acetoxypropionic acid (123) is readily prepared by the acylation of L-lactic acid with either acetic acid/sulfuric acid in benzene (50% yield) [79] or with an excess of acetyl chloride (80% yield) [80]. One is not limited exclusively to the use of lactic acid as the starting material. Diazotization of L-alanine in acetic acid furnishes 123 in 47% yield with at least 96% retention of configuration [48].

7) [122] (Scheme 54). In the synthesis of L-vancosamine (387) the required methyl substituent is introduced by alkylation of the enolate of 393 with methyl iodide. The methylation occurs from the less hindered side of the molecule to furnish 396 as a 96:4 mixture of ft and a-methyl isomers [123]. The remainder of the synthesis parallels that of L-daunosamine: lactol formation (73% yield), Wittig reaction (56% yield), and acid hydrolysis (46% HF-methanol, 33% yield). LDA 2. CH3I 'NHBOC *~ CH3,///^°N^O \ / ^\ L-CH3 69o/o HO' ^^ "—?

An example of this strategic approach is a six step synthesis of (S)-( — )-ipsenol (207), a constituent of the sex pheromone of the bark beetle, which is outlined in Scheme 29 [75]. LLactic acid is activated through formation of mixed anhydride 203, and subsequent addition of methylmagnesium bromide furnishes methyl ketone 204. Aldol condensation of enol silyl ether 205 with isovaleraldehyde gives the adduct 206 (89% ds). The synthesis is completed by Wittig olefination followed by hexakis(te7t-butylisonitrile)molybdenum-catalyzed elimination of the pivalate to give 207 in 21% overall yield for the six step sequence.

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Alpha-Hydroxy Acids in Enantioselective Syntheses by Gary M. Coppola
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