Alcohol , viii

The stereoselectivity of these reactions, exemplified by the hydrolysis of the isomeric acetates (VI and VII), is no less striking. Both of these esters undergo hydrolysis by uncatalyzed ionization to give the exo alcohol (VIII), but the rate of hydrolysis of VI is some 2000 times that of its endo... 

An exception to these general principles which has been reported is the reaction of a- or 7-ethylallyl alcohol with thionyl chloride. The primary isomer gives principally the secondary chloride, and from the secondary isomer the primary chloride predominates.4 It has been pointed out, however,5 that these results may be explained by an Sni type reaction of the intermediate chlorosulfinic ester in which a six-membered ring is involved. Thus for the transformation of a-ethylallyl alcohol (VIII) to 7-ethallyl chloride (IX), we have ... 

Hydroboration of alkenes was first developed by Brown [26, 27], a Nobel laureate for his contribution to the organic chemistry of boron. The process is based on a multi-step reaction. This consisted of syn-addition of borane to the C=C bond to form IV, followed by peroxide attack and Bayer-Williger-type rearrangement of the intermediate boron-peroxide V-VI, and finally hydrolytic splitting of the boronate ester VII to the prim-alcohol VIII, as outlined in Scheme 6.9. 

To a suspension of a tinc-copper couple in 150 ml of 100 ethanol, prepared from 80 g of zinc powder (see Chapter II, Exp. 18), was added at room temperature 0.10 mol of the acetylenic chloride (see Chapter VIII-2, Exp. 7). After a few minutes an exothermic reaction started and the temperature rose to 45-50°C (note 1). When this reaction had subsided, the mixture was cooled to 35-40°C and 0,40 mol of the chloride was added over a period of 15 min, while maintaining the temperature around 40°C (occasional cooling). After the addition stirring was continued for 30 min at 55°C, then the mixture was cooled to room temperature and the upper layer was decanted off. The black slurry of zinc was rinsed five times with 50-ml portions of diethyl ether. The alcoholic solution and the extracts were combined and washed three times with 100-ml portions of 2 N HCl, saturated with ammonium chloride. 

In the flask were placed 0.40 mol of dry, powdered copper(I) cyanide, 9 g of anhydrous lithium bromide (note 1), 50 ml of dry THF and 0.30 mol of l-bromo-2--heptyne (prepared from the corresponding alcohol and PBrs in diethyl ether, see VIII-2, Exp. 10). The mixture was heated until an exothermic reaction started, which occurred at about 80°C. The solid dissolved gradually. The mixture was kept... 

The preparation of thiazole alcohols by reduction is also discussed in Chapter VIII. 

This synthesis came shortly after one by Prelog, Kohlberg, Cerkovnikov, Rezek and Piantanida (1937) based on a series of reactions which, with modifications and extensions. Prelog and his colleagues have applied to the syntheses of bridged heterocyclic nuclei, of which this is an example. 4-Hydroxymethyltetrahydropyran (VI R =. OH) is converted via the bromo-compound (VI R = Br) and the nitrile (VI R = CN) into tetrahydropyran-4-acetic acid of which the ethyl ester (VII) is reduced to 4-()3-hydroxyethyl)-tetrahydropyTan (VIII). This is converted by fuming hydrobromic acid into 3-(2-bromoethyl)-l 5-dibromopentane (IX) which with ammonia in methyl alcohol yields quinuclidine (V). 

Borohydrides reduce a-substituted ketones to the corresponding a-substituted alcohols, and such products can be further reduced to olefins (see section VIII). Other reagents serve, through participation of the carbonyl group, to remove the substituent while leaving the ketone intact. The zinc or chromous ion reduction of a-halo ketones is an example of this second type, which is not normally useful for double bond introduction. However, when the derivative being reduced is an a,jS-epoxy ketone, the primary product is a -hydroxy ketone which readily dehydrates to the a,jS-unsaturated ketone. Since... 

During the course of this work Tamura et al. (1,14,15) isolated a metabolite from another strain of Helminthosporium sativum. By comparison with the bis-3,5-dinitrobenzoate of the diol from helminthosporal they identified it as the unsaturated aldehyde-saturated alcohol, helminthosporol (VIII, IX). 

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