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

By Gary M. Coppola

Recognition 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 very important 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 express how chiral facilities inherent in those basic compounds can be utilized to regulate the creation of extra stereogenic facilities. Readers can without delay observe new variations of their personal paintings due to the fact that response stipulations are given in convenient tables.

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6 Methoxy methyl (MOM) (iS)-2-(Methoxymethoxy)propanoic Acid Protection of ethyl L-lactate with a MOM group (377) can be effected in high yield with either chloromethyl methyl ether in the presence of Hunig's base [100,119] or with dimethoxymethane and phosphorus pentoxide [120]. H C,CH2OCH3 /-Pr2NEt, CH2CI2 85% 91% 377 The chiral bicyclic lactam-lactone fragment of the antibiotic neooxazolomycin (378) has been synthesized using the MOM-protected methyl L-lactate analog 379 as the source of chirality [121] (Scheme 52).

5% ee), which has been carried on to triazolylmethyloxirane (25, 3*S)-250, an intermediate in the preparation of triazole antifungal agents (Scheme 35). If 245 is not inverted but carried through the same synthetic sequence via (R)-256 is produced. 1. Another approach to (25, 3R)-256 uses intermediate 245 and a Grignard reaction to introduce the necessary elements [87] (Scheme 36). 5% ee); (e) DHP, PPTS, CH2CI2; (f) (dimethylisopropoxysilyl)methylmagnesium chloride, ether; (g) NaHCO3 , H2O2 , THF / MeOH; (h) PTSA, MeOH; (i) MsCI, pyridine (96%); (j) triazole, NaH, DMF OR b, c 99% [— 245 OH 1 CH3 R=H = THP 252 253 H O 254 255 256 Scheme 36 conditions: (a) DHP, PPTS, CH2CI2 ; (b) vinylmagnesium bromide, THF; (c) H + ; (d) MsCI, pyridine; (e) NaH, DMF; (f) OsO4 , NalO4 , MeOH-H2O; (g) NaBH4 , MeOH (70% from 253); (h) MsCI, Et3N, CH2CI2 ; (i) triazole, NaH, DMF 35 36 1 Lactic Acid Various 2-furanone chiral building blocks are readily accessible from (9-acetyllactate derivative 222 according to the series of reactions outlined in Scheme 37.

This intermediate has been used for the synthesis of a variety of Cbz-protected D-amino acids [66] (Scheme 25). 2 Inversion Reactions 25 (Z)-Allylic selenides 179 are formed in 58—69% yield under Wittig conditions using saltfree alkylidene triphenylphosphorane. Af-Chlorosuccinimide/carbamate-promoted [2,3]-sigmatropic rearrangement affords allylic amines 180 in 45—64% yield. The olefin is transformed to an acid by conversion to an aldehyde followed by Jones oxidation. The resulting D-amino acids 181 are produced in 58—72% yield with enantiomeric excess values of 78—84%.

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