Reduction reactions allylic alcohol

To gain mechanistic insight into the reduction of allylic alcohol 46, the reaction was monitored by measuring the hydrogen evolution and ReactIR3). The addition of 0.5 equiv of Red-Al resulted in the evolution of 2 mol of H2 and the formation of the dimeric intermediate 83 (Scheme 7.26) [19b, 30], Figure 7.2 shows the cumulative evolution of hydrogen (mmol) and the cumulative amount of Red-Al ... 

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. 

As this reaction proceeds, [rr-allyl PdClJg is gradually formed. Since the 77-allyl group represents a reduction of allyl alcohol, it has been suggested that allyl alcohol reacts with PdCl2 to give the 77-allyl complex and CeHioOa (750) ... 

Chen s stereospecific total synthesis of cycloeudesmol 48 started with the hydrazone 46, which was converted to the allylic alcohol 47 by the Bamford-Stevens reaction followed by DMF trapping of the vinyl anion and sodium borohydride reduction. This allylic alcohol 47 was then taken on through a further ten steps to yield the natural product cycloeudesmol 48. 

In the case of a,p-unsaturated ketones, chiral binaphthophosphepine ligands L5 exhibited a clear preference towards 1,2-reduction. Thus, allylic alcohols 16 and 22 were formed in high yield and with high enantioselectivity using L5 (R=Ph). The reaction with benzylidene acetone was less selective 1,2-manifold was in competition with 1,4-manifold and a complete reduction pathways, which was also accompanied by a drop in enantiocontrol [14]. 

Kumar and Dittmer have reported the synthesis of intermediates for the lactone moiety of mevinic acids using tellurium-induced nucleophilic reduction developed by their own group as the key step [122] (Scheme 75). Alcohol 331 was protected and converted into aldehyde 332, which upon Wittig reaction and reduction gave allylic alcohol 333. Sharpless epoxidation of 333 and tosylation of the primary alcohol afforded tosylate 334, which underwent the tellurium-induced transposition providing lactone 335 through spontaneous lactonization. However, in the case of the corresponding fcrf-butyl ester, there was no spontaneous lactonization observed. 

Cycloadduct 172 was subsequently converted in 177 over a five-step reaction sequence (Scheme 19.40). Epoxidafion followed by reduction afforded allylic alcohol 178. Inversion of the alcohol stereocenter was accomplished by an oxidation/reduction sequence of reactions to provide... 

The mechanism of the reduction of allylic alcohols (Scheme 28) has been studied in detail. The aldehyde is rapidly reduced to the allylic alcohol and its level stays low and constant during reaction. The aldehyde present at equilibrium conditions is then transformed into the saturated aldehyde and then into the final product. The reduction reaction described in Scheme 28 has been scaled to hundreds of grams for the preparation of C5 chiral synthons [149]. 

Wohf-Kishner reductions of a,jS-epoxy ketones give allylic alcohols, thus providing a means of reversing the arrangement in a,jS-unsaturated ketones or allylic alcohols. The reaction as first described by Wharton proceeds very readily (at room temperature in some instances) and the addition of strong base is unnecessary for example, the reduction of the epoxy ketone 143. 

Sharpless and Masumune have applied the AE reaction on chiral allylic alcohols to prepare all 8 of the L-hexoses. ° AE reaction on allylic alcohol 52 provides the epoxy alcohol 53 in 92% yield and in >95% ee. Base catalyze Payne rearrangement followed by ring opening with phenyl thiolate provides diol 54. Protection of the diol is followed by oxidation of the sulfide to the sulfoxide via m-CPBA, Pummerer rearrangement to give the gm-acetoxy sulfide intermediate and finally reduction using Dibal to yield the desired aldehyde 56. Homer-Emmons olefination followed by reduction sets up the second substrate for the AE reaction. The AE reaction on optically active 57 is reagent... 

Catalytic reduction of codeine (2) affords the analgesic dihydrocodeine (7) Oxidation of the alcohol at 6 by means of the Oppenauer reaction gives hydrocodone (9)an agent once used extensively as an antitussive. It is of note that treatment of codeine under strongly acidic conditions similarly affords hydrocodone by a very unusual rearrangement of an allyl alcohol to the corresponding enol, followed by ketonization. 

A reiterative application of a two-carbon elongation reaction of a chiral carbonyl compound (Homer-Emmonds reaction), reduction (DIBAL) of the obtained trans unsaturated ester, asymmetric epoxidation (SAE or MCPBA) of the resulting allylic alcohol, and then C-2 regioselective addition of a cuprate (Me2CuLi) to the corresponding chiral epoxy alcohol has been utilized for the construction of the polypropionate-derived chain ]R-CH(Me)CH(OH)CH(Me)-R ], present as a partial structure in important natural products such as polyether, ansamycin, or macro-lide antibiotics [52]. A seminal application of this procedure is offered by Kishi s synthesis of the C19-C26 polyketide-type aliphatic segment of rifamycin S, starting from aldehyde 105 (Scheme 8.29) [53]. 

ALCOHOL represents a convenient method of converting allyl alcohol to 2-substituted 1-propanols, while a one-pot reaction sequence of alkylation (alkyl lithium) and reduction (lithium—liquid ammonia) provides excellent yields of AROMATIC HYDROCARBONS FROM AROMATIC KETONES AND ALDEHYDES. 

Finally, the necessity arose for the synthesis of pentulose 21, labeled with, 3C on the central carbons, C-2 and C-3, for an independent biosynthetic study, which is reported in Section III.5.27 The doubly labeled ester 34 (Scheme 14) is readily available by a Wittig- Homer condensation of benzyloxyacetaldehyde with commercially available triethylphosphono-(l,2-l3C2)acetate. Chirality was introduced by the reduction of ester 34 to the allylic alcohol, which produced the chiral epoxide 35 by the Sharpless epoxidation procedure. This was converted into the tetrose 36, and thence, into the protected pentulose 37 by the usual sequence of Grignard reaction and oxidation. 

The stereochemistry of the first step was ascertained by an X-ray analysis [8] of an isolated oxazaphospholidine 3 (R = Ph). The overall sequence from oxi-rane to aziridine takes place with an excellent retention of chiral integrity. As the stereochemistry of the oxirane esters is determined by the chiral inductor during the Sharpless epoxidation, both enantiomers of aziridine esters can be readily obtained by choosing the desired antipodal tartrate inductor during the epoxidation reaction. It is relevant to note that the required starting allylic alcohols are conveniently prepared by chain elongation of propargyl alcohol as a C3 synthon followed by an appropriate reduction of the triple bond, e. g., with lithium aluminum hydride [6b]. 

The enol ethers of P-dicarbonyl compounds are reduced to a, 3-unsaturated ketones by LiAlH4, followed by hydrolysis.115 Reduction stops at the allylic alcohol, but subsequent acid hydrolysis of the enol ether and dehydration leads to the isolated product. This reaction is a useful method for synthesis of substituted cyclohexenones. 

---