?-Hydroxy Acids in Enantioselective Syntheses by Garry M. Coppola, Dr. Herbert F. Schuster(auth.)

By Garry M. Coppola, Dr. Herbert F. Schuster(auth.)

Cognizance man made chemist!

Chiral alpha-hydroxy acids on hand from nature's chiral pool function beginning fabrics in a wide selection of enantioselective conversions resulting in commercially very important items. This monograph, a stimulating resource of principles and an important reference paintings for study chemists, makes a speciality of the well known lactic, mandelic, malic, and tartaric acids.

Well-chosen examples express how chiral facilities inherent in those easy compounds can be utilized to manage the creation of extra stereogenic facilities. Readers can at once observe new ameliorations of their personal paintings on the grounds that response stipulations are given in convenient tables.

Content:
Chapter 1 Lactic Acid (Part 1) (pages 1–64):
Chapter 1 Lactic Acid (Part 2) (pages 65–118):
Chapter 1 Lactic Acid (Part three) (pages 119–136):
Chapter 2 Mandelic Acid (pages 137–165):
Chapter three Malic Acid (Part 1) (pages 167–213):
Chapter three Malic Acid (Part 2) (pages 213–275):
Chapter three Malic Acid (Part three) (pages 275–312):
Chapter four Tartaric Acid (Part 1) (pages 313–368):
Chapter four Tartaric Acid (Part 2) (pages 368–424):
Chapter four Tartaric Acid (Part three) (pages 424–478):

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Extra info for ?-Hydroxy Acids in Enantioselective Syntheses

Example text

Even at this temperature reaction is complete within two hours to give 196 with greater than 96% ee. In comparison, Mitsunobu reaction between various lactates and Boc2NH gives negligible amounts of inversion products. One Boc group is removed with trifluoroacetic acid, after which the benzyl ester is hydrogenolyzed to the desired acid 198 in 83% overall yield from 195. This process is amenable to 15N-labelling. BuU CH2CI2 , pyridine THF 195 NHBoc ^ 197 X '^ 100% 85% 194 NBoc2 H2 , Pd / C 196 NHBoc MeOH 198 Scheme 27 Other nucleophiles react with equal facility with 189 [72] (Scheme 28).

The initial step of the reaction is the formation of phosphonate 95. The resulting liberated azide then completely displaces the phosphonate group, with nearly total inversion of the stereo center. OH OPO(OPh)2 N3 X 87% 95 ' 96 2-Nosyloxyesters undergo substitution reactions with inversion of configuration (Scheme 15). The corresponding nosyl lactate 98 is prepared in quantitative yield from 97 upon treatment with 4-nitrobenzenesulfonyl chloride in the presence of triethylamine and DMAP [34]. Reaction of 98 with sodium azide in DMSO (55 °C) gives the (^)-azidoester 99.

Et LDA, -78 °C t-Bu" °^'"CH3 t-Bu ^ RX 77 - 82% 56 59 583 R = CH2Ph (96% ds) 58b R = CH2CH=CH2 (98% ds) 58C R = Et (97% ds) LiAIH4 60 The enolate of 56 is highly nucleophilic and shows little basicity. Aldehydes as well as acetone, cyclopentanone, and acetophenone react readily to generate adducts in high yield. Dioxolanone 58c, when reduced to lactol 61, is a masked 1,4-dialdehyde (64) equivalent. The aldehyde, which is "freed" by ozonolysis and acidic hydrolysis, undergoes a Marschalk reaction with leucoquinizarine (65) to give rhodomycinone 66 in 45% yield [22] (Scheme 9).

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