Alcohol chiral

Strategy An alcohol is a compound that contains the -OH functional group. To make an alcohol chiral, we need to have four different groups bonded to a single carbon atom, sav -H, -OH, -CHj, and -CH9CH3. 

For other chiral reagents and application of this method to other classes of compounds, such as a-amino esters, a-hydroxy esters, amino alcohols, chiral a-deuterated benzylamine, phosphorus compounds, and the use of nuclei other than hydrogen (l3C, 19F), see reference 186 and Section D.4.1. 

The starting 2-(l-alkoxynaphth-2-yl)-4,5-dihydro-4,4-dimethyl-l,3-oxazoles are prepared by treatment of the bromo-4,5-dihydro-l,3-oxazole derivative with sodium alkoxide in DMF at 50 °C, or by transesterification reactions in which the methoxy-4,5-dihydro-l,3-oxa7ole derivative is heated with the appropriate chiral alcohol/chiral sodium alkoxide mixture29. 

One of the early syntheses of orlistat (1) by Hoffmann-La Roche utilized the Mukaiyama aldol reaction as the key convergent step. Therefore, in the presence of TiCU, aldehyde 7 was condensed with ketene silyl acetal 8 containing a chiral auxiliary to assemble ester 9 as the major diastereomer in a 3 1 ratio. After removal of the amino alcohol chiral auxiliary via hydrolysis, the a-hydroxyl acid 10 was converted to P-lactone 11 through the intermediacy of the mixed anhydride. The benzyl ether on 11 was unmasked via hydrogenation and the (5)-7V-formylleucine side-chain was installed using the Mitsunobu conditions to fashion orlistat (1). 

Keywords Asymmetric hydrogenation, Asymmetric transfer hydrogenation, BINAP, Chiral alcohols, Chiral amines, Homogeneous catalysts, Simple ketones... 

Enantioselective oxidation of achiral selenides and their subsequent rearrangement would provide optically active alcohols. Chiral alkyl arylselenoxides racemize quickly in the presence of moisture via an acid-catalyzed formation of an achiral hydrate. However, bulky ortho substituents in the aryl moiety slow down the rate of racemization by sterically inhibiting the formation of this hydrate. 

Other Applications. Chiral oxazaborolidines derived from ephedrine have also been used in asymmetric hydroborations, and as reagents to determine the enantiomeric purity of secondary alcohols. Chiral l,3,2-oxazaborolidin-5-ones derived from amino acids have been used as asymmetric catalysts for the Diels-Alder reaction,and the aldol reaction. ... 

Faller, J. W., Sams, D. W. I., Liu, X. Catalytic Asymmetric Synthesis of Homoallylic Alcohols Chiral Amplification and Chiral Poisoning in a Titanium/BINOL Catalyst System. J. Am. Chem. Soc. 1996,118, 1217-1218. 

Fig. 1. Chemical structure of (-)-epinephrine. Individual moieties, including the meta- and para-hydroxyls, catechol ring, protonated amine, alcoholic chiral p-carbon hydroxyl, and A-methyl group are indicated.

Homopropargyl and allenyl alcohols. Chiral silanes are formed from propargylic mesylates. Subsequent reaction with aldehydes proceeds in a manner depending on the substituent on the sp-carbon of the mesylates. Starting from nonracemic mesylates the products are obtained with excellent ee. 

In general, the chiral hydride reagent is generated in situ by reaction of a suitable metal hydride with chiral ligands such as alkaloids , sugar derivatives , amino alcohol chiral oxazolines tartaric acid derivatives chiral amines and chiral diols... 

To synthesize a large amount of enantiopure chiral MaNP acid (3), the facile synthesis and enantioresolution of racemic acid 3 were carried out as shown in Fig. 9.9. In general, for enantioresolution of carboxylic acids, chiral synthetic amines or alkaloids have been used. However, we have adopted the following novel strategy using chiral alcohols chiral alcohols are condensed with racemic acid 3 and the diastereomeric esters formed are separated by HPLC on silica gel. 

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