Alcohols reductive transpositions

Reductive Transposition of Allylic Alcohols. Similar to the synthesis of allenes from propargylic alcohols, the Mitsunobu displacement of allylic alcohols with IPNBSH followed by hydrolysis, diazene formation, and sigmatropic loss of dinitrogen provides reductively transposed alkenes. This methodology has proven effective for the reductive transposition of a variety of allylic alcohols (eq 2). The overall transformation provides the desired olefin with high selectivity in the formation of the irans-alkene (eq 3). ... 

For reduction of allylic alcohols with double bond transposition, see page 229, Section 4. 

See also page 47, Section 93 and page 49, Section 9.4, for reduction of sulfur-containing derivatives of alcohols and phenols and page 229, Section 4, for reduction of allylic sulfonates and sulfones with double bond transposition. 

A recently published full account of another synthesis [69] of the same alkaloid starting from the /rans-cinnamic ester 264 represented a different approach (ACD -> ACDB) to ( )-lycorine (Scheme 42). An intramolecular Diels-Alder reaction of 264 in o-dichlorobenzene furnished the two diastereomeric lactones 265 (86%) and 266 (5%) involving the endo and exo modes of addition respectively. The transposition of the carbonyl group of 265 to 267 was achieved by reduction with lithium aluminium hydride, followed by treatment of the resulting diol with Fetizon s reagent, which selectively oxidised the less substituted alcohol to give isomeric 5-lactone 267. On exposure to iodine in alkaline medium 267 underwent iodolactonisation to afford the iodo-hydroxy y-lactone 268. The derived tetrahydropyranyl ether... 

Scheme 12.6). Stereoselective reduction and chromatographic separation afforded diastereomerically pure derivative 32 in 94% ee. Removal of the silicon protecting group, followed by acetylation of the two secondary alcohols, set the stage for an elegant palladium-catalyzed allylic transposition that provided compound 33 with...

In these compounds, there is a marked relationship between molecular geometry and biological activity. From values reported in the literature and according to our own studies, the E isomers, in which the residue originating from the aldehyde is in the transposition to the triazole, are markedly superior to the Z isomers in their biological activity. By suitable control of the reaction conditions, it is possible to achieve an almost complete isomerization to the unsaturated E-triazolylketones. Subsequent reduction leads to the more active E-alcohols. This group of N-vinylazoles includes the triazole derivative S 3308 (Sumitomo), currently under development as... 

Hydroboration of trimethyhilyl enol ethers. This reaction can be used to effect reductive 1,2-transposition of acyclic ketones (equation I). Highest yields of the transposed alcohol are obtained when = H. 

Allylphosphine oxides may be used to make allyl alcohols by the reductive removal of the Ph2PO group with LAH. The reaction involves transposition of the double bond (equation Li(Bu 0)3AlH breaks selectively the C—P phosphonate bond, and this reagent is chemoselective and can... 

Reactions of Enols and Enolate Anions.—Several methods are described for transposition of an oxo-function to the adjacent site. They involve formation of a suitable a-substituted derivative (hydroxymethylene ° or benzylidene ) and subsequent steps which transform the substituent into an isolated oxo-group. Condensations leading to both the 2-hydroxymethylene- and the 2-arylidene-3-oxo-steroids are described for 3-ketones of the 5jS-series, and also of the 5j8,9j5,10a-( retro ) series.Condensations of aromatic aldehydes at C-2 in the 5 -series are unusually slow enolisation towards C-4 is preferred, but steric compression between C-4 and C-6 in 5/3-compounds severely hinders the condensation reaction at C-4, allowing reaction at C-2 via the 2-enol. Reduction of a 21-hydroxymethylene-pregnan-20-one (337) with sodium borohydride afforded the homopregnanediol (338), although reduction of enolised P-dicarbonyl compounds frequently proceeds via elimination to give enones, and thence allylic alcohols. 

The Wharton reaction is the transformation of a,(3-epoxy ketones 1 by hydrazine to allylic alcohols 2. It is also known as the Wharton transposition, Wharton rearrangement, and Wharton reduction. 

The next phase of the synthesis involved the transposition of aldol adduct 61 to the protected "aldol" adduct 60. (3-Hydroxyketone 61 was subjected to conditions (NaBH4, AcOH) which effected a direct reduction of the carbonyl moiety of 61 and thereby introduced the axial C(9) hydroxyl functionality of 67 with complete stereocontrol through an intramolecular delivery of hydride within an alkoxide intermediate at C(7). After diprotection of both hydroxyl groups of 67, chemoselective deprotection of hydroxyl at C(7) and Swern oxidation, ketone 60 was isolated. The enolate derivative of 60 could be stereoselectively p-methoxybenzylated, and the resulting ketone was reduced to the wrong equatorial alcohol 68. The C(7) stereogenic center was inverted by treatment of the nosylate derivative of 68 with rubidium acetate to afford the desired acetate 69 accompanied by the syn elimination product (15%). 

Ni(U)-catalyzed Grignard reaction, furnishing allylic alcohols. Allylic ethers are also reactive when there is a phosphine group to coordinate Ni. Note that Grignard reagents which can act as hydride donors give products of reductive cleavage of the allylic ethers without transposition of the double bond. ... 

It is a reagent used for allylic transposition, de-bromination and reduction of alcohols in the presence of DEAD and PhsP. [Movassaghi et al. Angew Chem. IntEd Engl 45 5859 2006, Movassaghi Ahmad 7. Org. Chem. 72 1838 2007],... 

It is a reagent used for ally lie transposition, de-bromination and reduction of alcohols in the presence of DEAD... 

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