Chemoselectivity epoxide reduction

Epoxide (36) can be made from (37) by chemoselective epoxidation of the more substituted and therefore more nucleophilic double bond. Non-conjugated diene (37) is an obvious Birch reduction product as both elearon-donating substituents are on the double bond and therefore away from the anions. 

Alkyl phenyl telluriums, obtained from alkyl halides and arenetellurolates, are reduced by triphenyl tin hydride to alkanes under mild conditions1. The alkanes were obtained in yields ranging from 71 to 95%. 5oe-Cholestan-3a-yl phenyl tellurium was similarly reduced to 5 a-cholestane in 89% yield. The reaction appears to be highly chemoselective as indicated by the reduction of an epoxide to an alcohol in the presence of a carbonyl group1. 

Although Smh is more chemoselective than traditional dissolving metal reagents, it does react with sulfoxides, epoxides, the conjugated double bonds of unsaturated ketones, aldehydes and esters, alkyl bromides, iodides and p-toluenesulfonates. It does not, however, reduce carboxylic acids, esters, phosphine oxides or alkyl chlorides. In common with most dissolving metal systems, ketones with an a-hetero substituent suffer loss of the substituent rather than reduction of the carbonyl group. ... 

Alane (AIH3) and its derivatives have also been utilized in the reduction of carboxylic acids to primary alcohols. It rapidly reduces aldehydes, ketones, acid chlorides, lactones, esters, carboxylic acids and salts, tertiary amides, nitriles and epoxides. In contrast, nitro compounds and alkenes are slow to react. AIH3 is particularly useful for the chemoselective reduction of carboxylic acids containing halogen or nitro substituents, to produce the corresponding primary alcohols. DIBAL-H reduces aliphatic or aromatic carboxylic acids to produce either aldehydes (-75 °C) or primary alcohols (25 C) Aminoalu-minum hydrides are less reactive reagents and are superior for aldehyde synthesis. ... 

Xylitol has been derived from the product of photo-oxidation of cyclopentadiene [204], (Z)-(4RS)-4,5-epoxypent-2-enal (Scheme 13.105). Chemoselective reduction of the formyl group gives cis-hydroxyepoxypentene 448, which is directly acetylated into 449. Treatment of 449 with tetrabutylammonium acetate in AC2O opens the epoxide with formation of 450. De-O-acetylation gives 451, the epoxidation of which with p-nitroperbenzoic acid generates a 3 7 mixture of epoxides 452 and 453, isolated as peracetates. The major epoxide 453 is hydrolyzed into xylitol via the orthoester 454. 

Lithium tri-t-butoxyaluminum hydride readily reduces aldehydes and ketones to the corresponding alcohols and reduces acid chlorides to aldehydes. Epoxides, esters, carboxylic acids, tert-amides, and nitriles are not, or only slowly, reduced. Thus, the reagent may be used for chemoselective reductions. ... 

Lithium tri-fert-Butoxyaluminohydride is a bulky chemo- and stereoselective hydride reducing agent. Aldehydes are reduced chemoselectively in the presence of ketones and esters at low temperature. Ethers acetals, epoxides, chlorides, bromides, and nitro compounds are unaffected by this reagent. Reviews (a) Seyden-Penne, J. Reductions by the Alumino- and Borohydrides in Organic Synthesis Wiley-VCH NewYork, 1997, 2" edition, (b) Malek, J. Org. React. 1985, 34, 1-317. 

Baeyer-Villiger oxidation (p. 853) catalytic hydrogenation (p. 844) chemoselective reaction (p. 848) dissolving-metal reduction (p. 846) enantioselective reaction (p. 857) epoxidation (p. 855) functional group interconversion (p. glycol (p. 858)... 

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