Allyl alcohols reduction

The TBS protecting group is selectively cleaved in the first step. The released propargylic alcohol is then reduced with Red-AI to an allylic alcohol. Reduction of the propargylic alcohol occurs selectively trims. Since during this reaction a five-membered ring system 41 is created through coordination of aluminum with the alkox-ide, it is assured that aluminum is located m the 3-position relative to the alkoxide. 

The structure of a polymeric support considerably affects catalyst activity. The decrease in the rate of allyl alcohol reduction with the chosen catalysts occurs in the sequence P4VP-Pd(0)>P2VP-Pd(0)>P2M5VP-Pd(0). The structure of coordination compounds of polyvinylpyridines with transition metal chlorides has been described in detail [76-79]. 

Et3SiH has been used to reduce p-trifluoromethylacetc henone to the alcohol, deoxygenate allyl alcohols, reductively alkylate enol esters using t-BuHgQ. ring open oxaziridines with enantioselective conversion to the silanol, while (H2CsCHSiMe2)2X cyclise to the disilacyclohexane and cyclopentane under radical conditions. ... 

Conversion of a-haloketones to olefins using hydrazine (via enedlitnides C-C-N NH). Also reduction of o,3-epoxy ketones to allyl alcohols. 

The reduction of allylic systems is frequently used to generate isolated double bonds. Suitable systems are obtained from oe,jS-unsaturated ketones via allylic alcohols (ref. 185, p. 256 ref. 283, 284) for example, the preparation of A" -cholestene (135). 

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... 

When the furanones 110 (R = Ph, p-MeOC6H4, p-Cl—C6H4) were subjected to reduction using sodium borohydride, neither the glycols 111 nor the allyl alcohols 112 were formed. Instead, the corresponding 4-(arylmethylene)-2,3-(4//,5// )-furandiones 113 were obtained (Scheme 34) (86JHC199). 

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. 

Carbonyl reduction begins to compete with olefin saturation when the double bond is hindered or the carbonyl is aromatic or an aromatic vinylog. In conjugated systems, deoxygenation may occur via an intermediate allylic alcohol (51). 

The synthesis of the trisubstituted cyclohexane sector 160 commences with the preparation of optically active (/ )-2-cyclohexen-l-ol (199) (see Scheme 49). To accomplish this objective, the decision was made to utilize the powerful catalytic asymmetric reduction process developed by Corey and his colleagues at Harvard.83 Treatment of 2-bromocyclohexenone (196) with BH3 SMe2 in the presence of 5 mol % of oxazaborolidine 197 provides enantiomeri-cally enriched allylic alcohol 198 (99% yield, 96% ee). Reductive cleavage of the C-Br bond in 198 with lithium metal in terf-butyl alcohol and THF then provides optically active (/ )-2-cyclo-hexen-l-ol (199). When the latter substance is treated with wCPBA, a hydroxyl-directed Henbest epoxidation84 takes place to give an epoxy alcohol which can subsequently be protected in the form of a benzyl ether (see 175) under standard conditions. 

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