Allylic hydroxyls, hydrogenolysis

Vinylogs of benzylic alcohols, e.g. cinnamyl alcohol, undergo easy saturation of the double bond by catalytic hydrogenation over platinum, rhodium-platinum and palladium oxides [39] or by reduction with lithium aluminum hydride [609]. In the presence of acids, catalytic hydrogenolysis of the allylic hydroxyl takes place, especially over platinum oxide in acetic acid and hydrochloric acid [39]. 

From these considerations and on biogenetic grounds, the structure XC was proposed (102) as a hypothetical one for C-fluorocurarine. This was confirmed (107) as follows. Hydrogenolysis of the allylic hydroxyl... 

The ease of hydrogenolysis of one hydroxyl indicated that it is allylic. (Platynecine does not undergo hydrogenolysis.) The allylic hydroxyl is probably the primary hydroxyl since —... 

Lasiocarpinic acid was considered to be esterified with the allylic hydroxyl of heliotridine because of its isolation in the hydrogenolysis of the alkaloid. The angelic acid was considered to be esterified with the 7-hydroxyl of heliotridine since this linkage was not easily reduced. 

A benzyl carbonate was prepared in 83% yield from the sodium alkoxide of glycerol and benzyl chloroformate (20°, 24 h). It was also prepared by a lipase-catalyzed ester exchange with allyl benzyl carbonate. It is cleaved by hydrogenolysis (H2/Pd-C, EtOH, 20°, 2 h, 2 atm, 76% yield) and electrolytic reduction (—2.7 V, R4N X, DMF, 70% yield). A benzyl carbonate was used to protect the hydroxyl group in lactic acid during a peptide synthesis." ... 

Results of the reduction of unsaturated alcohols depend on the respective positions of the hydroxyl and the double bond. Since the hydroxyl group is fairly resistant to hydrogenolysis by catalytic hydrogenation almost any catalyst working under mild conditions may be used for saturation of the double bond with conservation of the hydroxyl [608]. In addition, sodium in liquid ammonia and lithium in ethylamine reduced double bonds without affecting the hydroxyl in non-allylic alcohols [608]. 

With few exceptions [609], unsaturated alcohols with hydroxyls in allylic positions undergo hydrogenolysis and give alkenes. Such reductions were achieved by chloroalanes made from lithium aluminum hydride and alu-... 

The degradation of the Senecio alkaloids continues to be effected by saponification or hydrogenolysis. The use of alkali in the hydrolysis does not alter the necine moiety but it may cause a change in the geometrical configuration about an a,j8-oarbon-carbon double bond in the necic acid. Hydrogenolysis provides important information as to the location of the esterified hydroxyl on the necine, and subsequent conversions permit a decision as to which end of a dicarboxylic necic acid (in the cyclic diesters) is attached to the allylic or primary hydroxyl of the necine. 

Oxidation with lead dioxide in 5% phosphoric acid yielded acetaldehyde and formaldehyde. Catalytic reduction in the presence of platinum resulted in the absorption of 1.5 mole equivalents of hydrogen and the isolation, by its steam volatility, of nearly 0.6 mole of a-methylbutyric acid. The carbon skeleton of sarracinic acid was thus determined, and the accompanying hydrogenolysis (some nonvolatile acid was also obtained) established that the double bond and hydroxyl constituted an allylic alcohol moiety. Since further data (spectroscopic data would be especially valuable) were not available, Danilova and Kuzovkov (127) were limited to the conclusion that sarracinic acid could be represented by one of three possible structures (CLXIa-c) ... 

Platynecine was not further reduced by hydrogen and nickel catalyst or platinum catalyst (58). Hydrogenolysis of monobenzoylplatynecine was not possible in the presence of nickel or platinum,whereas monobenzoyl-retronecine was readily hydrogenolyzed under the same conditions. These results indicated that hydrogenation of the labile hydroxyl and of groups replacing it (OOCR, Cl) was dependent upon the presence of the double bond, and that the labile hydro.xyl was probably allylic. 

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