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

By Gary M. Coppola

Consciousness man made chemist! Chiral alpha-hydroxy acids to be had 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 a necessary reference paintings for examine 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 regulate the creation of additional stereogenic facilities. Readers can at once observe new modifications of their personal paintings considering that response stipulations are given in convenient tables.

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Extra resources for Alpha-Hydroxy Acids in Enantioselective Syntheses

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By adjusting the oxidation state of the carbon adjacent to the asymmetric center prior to rearrangement one can gain access to chiral a-methyl esters 363 [114] (Scheme 50). =H) or dissolving metal reduction, which gives the £-isomer (Rl=C4H9, R2=H). 78° _> -20 °C; (e) Swern oxidation; (f) CH3CH=CHCH2Br, CrCI2 , THF; (g) DHP, PPTS (94%); (h) (c-C6H11)2BH, THF, then H2O2 (97%); (i) KH, Mikolaiczyk reagent (76%); (j) HgCI2 , CH3CN - THF (92%); (k) LDA, CH3I, THF - HMPA, -78 °C (88%) cium carbonate occurs with complete retention of the olefin geometry and produces esters 363, which are optically pure.

3 O-Acyl Lactates 29 203 O O t-BuX^O t-Bu^^p ~~ 3 d ^ ». ~3 I OTMS 205 ^V^ fl E O OH ^ 206 II OH 207 Scheme 29 conditions: (a) f-C4H9COCI, 2-picoline (2 eq), DMAP (10 mol%), ethe r, 0 °C; (b) CH3MgBr, THF, -78 °C; (c) TMS-Tf, Et3N, benzene; (d) isovaleraldehyde, TiCI4 a series of reductions and dehydration, (2R, 45)-l,4-dihydroxy-2-methylpentane (213), the C-5 to C-9 fragment of the polypropionate unit of geodiamolide and jaspamide, is formed [76] (Scheme 30). a-Limiated derivatives of 216, which are configurationally stable at —70 °C, are useful in asymmetric homoaldol reactions.

OH OMEM /-Pr2NEt, CH2CI2 , 0 °C 59-90% 372 50 1 Lactic Acid B-Br OMEM OH CH2CI2, rt, 18 h 82% 372 CH3 Ph 364 365 366 CH3 CH3 ^x^\^ OCH2Ph CH3 367 368 CH3 CH3 CH3 CH3 369 CH3 370 CH3 371 Scheme 51 conditions: (a) 11b; (b) H3O+; (c) HOCH2C(CH3)2CH2OH, TMS-CI; (d) H2 , Pd - Pb, quinoline; (e) MsCI, pyridine; (f) DIBAL, Et3AI, toluene, -42 °C; (g) I2 , CaCO3 , CH2CI2 , 0 °C; (h) KOf-Bu, DMF (94%); (i) HS(CH2)3SH, BF3-Et2O (84%); (j) n-BuLi, BrCH2CH=C(CH3)2 (41%); (k) NCS, AgNO3 , CH3CN, H2O (72%) The chelative ability of the oxygen atoms in the MEM group results in an ideal environment for the addition of organolithium reagents to the ester group of 372.

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