Alcohol with exocyclic double bonds

Table 21.5 Diastereoselective hydrogenation of alcohols with exocyclic double bond. 

Of the four possible transition states for the [3,3] sigmatropic rearrangement of bicyclic endo-alcohols with exocyclic double bonds, the enrfo-chair transition state as shown below is kinetically strongly preferred. The intermediate enolate is exclusively protonated from the exo side, even if an exo-methyl group is present90. 

Intramolecular deoxygenation of alcohols containing double and triple bonds (such as hydroxyalkynes or hydroxynitriles) with ImCSIm leads via the corresponding thio-carbonylimidazolides to five- and six-membered cyclized systems with exocyclic double bonds.[72]... 

A small, structurally distinct class of 1 -substituted allylic alcohols consists of those that are conformationally restricted by incorporation into a ring system. These allylic alcohols may be further subdivided into two types, depending on whether the double bond is endocyclic or exocyclic. For allylic alcohols with endocyclic double bonds, kinetic resolution gives 2-cyclohexen-l-ol (71) with 30% ee [14], (4a.S, 2/ )-4a-methyl-2,3,4,4a,5,6,7,8-octahydro-... 

Treatment of (165) with SnCU gives exclusively (166). The selective formation of an axial alcohol and exocyclic double bond, a general characteristic of type 11 ene reactions, is required by either a concerted reaction or a stepwise reaction with an intramolecular proton transfer. Similar treatment of (167), as a mixture of isomers, gives the less stable isomer (168) with an axial alcohol and an equatorial methyl group, since the alcohol must be formed axial and the methyl group prefers to be equatorial in the transition state (Scheme 26). ... 

R)-lrans-Verbenol (77) is epoxidized five times as fast as (S)-/rarcs-verbenol when (+)-DlPT is used in the catalyst [77]. For allylic alcohols with an exocyclic double bond, kinetic resolution gives 2-methylenecyclohexanol (78) with 80% ee in 46% yield when (-)-DIPT is used [119]. 

The exocyclic double bond of the enamide 97 was reacted with diborane, followed by alkaline hydrogen peroxide addition, affording the trans-alcohol 98 <1996J(P1)545>. 

Double bonds with different geometry behave in a unique way. For example, the monohydroboration of caryophyllene (9) with dicyclohexylborane followed by oxidation brought about the participation of the (E)-trisubstitutcd double bond in preference to the exocyclic double bond during hydroboration to give the corresponding alcohol (10) (Eq. 10)50t. However, under similar conditions, isocaryophyllene (11), which has a (Z)-endocyclic double bond, affords a mixture of unsaturated alcohols... 

Phase-transfer addition (c/. Vol. 6, p. 31) of dibromocarbene to carvone and reduction to a monobromo-ketone by tributyltin hydride, or to a dibromo-alcohol with lithium aluminium hydride, is reported/ 1,3-Dipolar cycloaddition of acetonitrile oxide occurs exclusively at the exocyclic double bond in limonene to give (155 R = Me, X = Hi), whereas isoxazoline formation with carvone yields (155 R = Me, X —O) and the isomeric product from attack at the C-6 double bond benzonitrile oxide, however, only yields (155 R = Ph, X = 0 or NOH). A re-investigation of aqueous chlorination of a -terpineol indicates that the diequator-ial chlorohydrin (156) and the corresponding diaxial chlorohydrin are the major... 

Lu and co workers found that the asymmetric hydrogenation of the tri substituted or di substituted exocyclic double bond of N tosyl 4 alkylidene 1,3 oxazolidin 2 ones (74), which are enamides in nature, proceeds smoothly under the catalysis of neutral [Rh(COD)Cl]2 and (S) (+) DTBM SEGPHOS (73) with nearly quantitative yields and high enantioselectivities (Scheme 9.20) [64]. This method provided a novel way to prepare chiral N tosyloxazolidinones (75) with high enantiomeric excess, which can be converted into amino acids, amino alcohols, and piperidine derivatives. 

Alcohol (236) with an exocyclic double bond in the five-position of the dihydro-1,4-dithiepin ring was formed by ring-contraction of dithiocin (235) <77T2l5l>. 

Several syntheses are available to the 13,14-dihydroprostaglandins, some of which are metabolites of the E and F series. The first of these routes [143, 144] started from the formyl derivative (LVII) of the enol ether of cyclo-pentan-l,3-dione which on reaction with ethyl 6-bromosorbate and tri-phenylphosphine followed by selective catalytic reduction afforded the ester (LVIII). A second formylation followed by elaboration with n-hexanoyl-methylenetriphenylphosphonium chloride 1 to the ketone (LIX) which on reduction of the exocyclic double bond and acid-catalysed solvolysis in benzyl alcohol afforded the benzyl ether (LX) and its isomeric enol ether. Reduction with lithium tri-t-butoxyaluminium hydride to the corresponding 15-hydroxy-compound and palladium-charcoal catalysed hydrogenolysis followed by prolonged catalytic hydrogenation with rhodium-charcoal led to ( )-dihydro-PGEi ethyl ester. 

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