Hydrogenolysis allyl alcohols

As a further application of the reaction, the conversion of an endocyclic double bond to an c.xo-methylene is possible[382]. The epoxidation of an cWo-alkene followed by diethylaluminum amide-mediated isomerization affords the allylic alcohol 583 with an exo double bond[383]. The hydroxy group is eliminated selectively by Pd-catalyzed hydrogenolysis after converting it into allylic formate, yielding the c.ro-methylene compound 584. The conversion of carvone (585) into l,3-disiloxy-4-methylenecyclohexane (586) is an example[382]. 

The Pd-catalyzed hydrogenolysis of vinyloxiranes with formate affords homoallyl alcohols, rather than allylic alcohols regioselectively. The reaction is stereospecific and proceeds by inversion of the stereochemistry of the C—O bond[394,395]. The stereochemistry of the products is controlled by the geometry of the alkene group in vinyloxiranes. The stereoselective formation of stereoisomers of the syn hydroxy group in 630 and the ami in 632 from the ( )-epoxide 629 and the (Z)-epoxide 631 respectively is an example. 

Reduced furans are formed in two types of oxypalladation processes on substrate a,ft- and y,<5-unsaturated alcohols. In an unusual reaction, allyl alcohol is converted into 4-methylenetetrahydrofurfuryl alcohol, among other products (Scheme 57)97 the formation of propene is thought to arise by reductive hydrogenolysis of allyl alcohol. 

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]. 

Unsaturated epoxides are reduced preferentially at the double bonds by catalytic hydrogenation. The rate of hydrogenolysis of the epoxides is much lower than that of the addition of hydrogen across the carbon-carbon double bond. In a, -unsaturated epoxides borane attacks the conjugated double bond at -carbon in a cis direction with respect to the epoxide ring and gives allylic alcohols [660], Similar complex reduction of epoxides occurs in a-keto epoxides (p. 126). 

The hydrogenolysis of the allyl ester 315 produced 316 regio- and stereoselectively. The free allyl alcohol in the same molecule was not attacked [136],... 

The method of choice for the hydrogenolysis of primary allylic alcohols involves treatment with a pyridine-S03 complex (to form a sulfoester) followed by reduction with LiAlH4. " This method eliminates complications encountered for the reactions in allylic systems, such as double bond migration or stereoisomerization ... 

The mechanisms of most alcohol reductions are obscure. Hydrogenolysis of benzyl alcohols can give inversion or retention of configuration, depending on the catalyst. The mechanism of electroreduction of allylic alcohols in acidic aqueous media has been examined. 

Basic supports for the palladium catalyst can also be used to inhibit the hydrogenolysis of allyl alcohols (Eqn. 16.22) and acetates (Eqn. 16.23). The addition of quinoline to the reaction mixture has the same effect (Eqn. 16.24). 5... 

Allyl alcohols are deoxygenated under the same conditions used to break a benzyl oxygen bond. Over a palladium catalyst, loss of oxygen occurs along with double bond saturation. The presence of acids promotes hydrogenolysis. With platinum, nickel, or rhodium catalysts in neutral medium, progressively less oxygen... 

The cleavage of the oxygen-oxygen bond in hydroperoxides to give the alcohols takes place over platinum, >180 palladium > 82 anj Raney nickel 3 catalysts at room temperature and atmospheric pressure (Eqn. 20.70). The use of Lindlar s catalyst or a similarly deactivated catalyst is preferred for the cleavage of allyl hydroperoxides in order to minimize the hydrogenolysis of the resulting allyl alcohol (Eqn. 20.71). 2,183... 

Hydrogenolysis of dialkylperoxides or epidioxides (cyclic peroxides) also takes place over these same catalysts under mild conditions. If tertiary alcohols are the products, running the reaction in acid media can lead to dehydration. Deactivated catalysts are also needed if the product contains an allyl alcohol that could be cleaved by the more active catalysts (Eqn. 20.72). 6.I87... 

Yamaguchi employed a strategy not unlike the Bartlett approach to brefeldin A, as depicted in Scheme 1.40. Keto diacid 189 was esterified and reduced with Ra(Ni) to afford a 92% yield of 245. Alcohol participation in a jyn-selective hydrolysis followed by reesterification with benzyl alcohol led to the formation of 246a and 246b in a 19 1 ratio. Protection of the alcohol as the acetate and hydrogenolysis of the benzyl ester followed by fractional recrystallization gave a 87% overall yield of 247. Acid 247 was converted to allylic alcohol 248 in 65% yield via Rosemund reduction of the derived acid chloride to the aldehyde and addition of vinylmagnesium bromide. 

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