Homo-allylic alcohols

Regioselective epoxidation of allylic and homo-allylic alcohols... 

The alkenyloxirane 126 in excess reacts with aryl and alkenyl halides or triflates in the presence of sodium formate to afford the allylic alcohol 127[104], Similarly, the reaction of the alkenyloxetane 128 gives the homo-allylic alcohol 130[105]. These reactions can be explained by insertion of the double bond in the Ar—Pd bond, followed by ring opening (or /3-eliraination) to form the allylic or homoallylic alkoxypalladium 129, which is converted into the allylic 127 or homoallylic alcohol 130 by the reaction of formate. The 3-alkenamide 132 was obtained by the reaction of the 4-alkenyl-2-azetizinone 131 with aryl iodide and sodium formate [106]. 

Many methods have been reported for the addition of allylic groups, including allyltrialkyltin compounds" (in the presence of BF3-etherate), as well as other allylic metal compounds." Allylic alcohols and homo allylic alcohols add to aldehydes in the presence of Sn(OT02 " For allylic halides, both activated... 

Allylzirconocene derivatives are reactive toward aldehydes, presumably because of the availability of six-centered transition states permitting an anti-selective synthesis of homo-allyl alcohols (Scheme 1.27) [115]. 

The reactions of allylmetal reagents with carbonyl compounds and imines have been extensively investigated during the last two decades [1], These carbon—carbon bondforming reactions possess an important potential for controlling the stereochemistry in acyclic systems. Allylmetal reagents react with aldehydes and ketones to afford homo-allylic alcohols (Scheme 13.1), which are valuable synthetic intermediates. In particular, the reaction offers a complementary approach to the stereocontrolled aldol process, since the newly formed alkenes may be readily transformed into aldehydes and the operation repeated. 

D. P. Curran, Z. Luo, Rapid, Parallel Synthesis of Homo-allylic Alcohols by Lewis Acid Mediated Allylations of Aldehydes with New Fluorous Allyl Stannanes , Med Chem. Res. 1998, 8,261. 

Similarly, 5-lactols and 5-lactones are obtainable from the corresponding homo allylic alcohols. With dehydration, the corresponding dihydropyrans are prepared. Spirocyclic y-butyrolactones of this type and the corresponding 5-lactones are widespread in nature and play a key role as synthetic intermediates. 

Diastereoselective hydrogenations of this type have been reported by Burgess and coworkers [54—59] using chiral-protected and -unprotected allylic and homo allylic alcohols as substrates with their carbene catalyst lr(9). Catalyst control was found to be dominant, but depending on the position and nature of the oxygen substituents, moderate to strong match/ mismatch effects were observed. 

By treating Nafion (NR-50), a perfluorinated acidic ion exchanger based on sulfonic acid groups, with scandium(III) chloride hexahydrate Kobayashi et al. generated a solid scandium-derived catalyst (29) (Nafion-Sc) that proved to be effective in al-lylation reactions of carbonyl compounds with tetraallyltin (Scheme 4.15). Since the catalyst is stable in both organic solvents and water, even unprotected carbohydrates could be transformed directly in aqueous solvents. The resulting homo-allylic alcohols were separated by simple filtration [97]. 

Y. Nakamura, M. Okada, H. Horikawa, T. Taguchi, Preparation of c5-fluorinated homo-allylic alcohol derivatives via regioselective hydride reduction of allylic alcohol derivatives, J. Fluor. Chem. 117 (2002) 143-148. 

A three-component reaction based on the umpolung of re-allylpalladium (II) complexes indium metal was reported by Grigg and co-workers (Scheme 8.31) [74]. In this reaction, the electrophilic nature of the n-allyl palladium species generated from aryl halides and allenes is reversed by transmetallation with indium metal. The resultant nucleophilic allylindium reagent subsequently adds to the third component - aldehyde [75] or imine [76] - to give the corresponding homo-allylic alcohol 64 or amine 65 respectively. 

A wide variety of silyl ethers can be employed, leading to functionalized homo-allylic alcohols or ethers. This three-component coupling reaction, which generates in a single operation a range of homoallylic ethers, does not require the initial and independent synthesis of the acetal (or ketal) derived from 6. 

Finally, (homo-)allylic alcohols were isomerised to their corresponding saturated ketones with good to excellent selectivity at 120°C in molten [(C4)4N]Br with either PdCl2, Pd(OAc)2 or palladium black.1133... 

Vinyllithium reageants, generated using Schlosser s reagent, attack monosubstituted oxiranes to produce homo-allylic alcohols (Equation 27) <1996T1433>. The addition reaction of lithiated alkynes to epoxides was observed to... 

Methylene ( CH2) addition to a double bond has been achieved by use of the Simmons-Smith reagent (CH2I2 and a zinc-copper couple) f 70J. The reaction gives a cyclopropane derivative by stereospecific cis addition, and in allylic or homo-allylic alcohols leads to methylene addition ci to the hydroxyl function. Examples in the steroid field include a s-methylene addition to the double bonds of the ga-hydrdxy-A dO), 3j8-hydroxy-AJ- and 3 a- and 3/9-hydroxy-A4 systems... 

Cyclopropanation of Allylic Alcohols. Simmons-Smith type cyclopropanation of the allylic alcohol 22 in the presence of a catalytic amount of the bis-sulfonamide la leads to formation of the corresponding cyclopropane 23 in high yield and selectivity (eq 6, Table 3). The reaction is rapid (< 1 h) and can be performed at low temperature (either 0 °C or —20 °C). Substrate scope encompasses both di- and tri-substimted allylic alcohols (24 and 26). However, substimtion at the 2 position, as in 28, leads to a drastic decrease in selectivity. The presence of additional oxygenated functionality (30) in the proximity of the alkene also lessens selectivity." The method is limited to the cyclopropanation of allylic alcohols. Other alkene-containing substrates, such as allylic ethers, homo-allylic alcohols and allylic carbamates, do not react with high selectivity. 

Samarium iodide promotes this addition reaction. " " In a related reaction, simple alkene units add to esters in the presence of sodium and liquid ammonia to give an alcohol.Structural variations in the alkene lead to different products. Homo-allylic alcohols react with aldehydes in the presence of Montmorillonite KSF clay to give 4-hydroxytetrahydropyrans. " A variation of this reaction converts an aryl aldehyde and a homoallylic alcohol to a 4-chlorotetrahydropyran in the presence of Homoallylic alcohols, protected as —O(CHMeOAc) react with... 

Homo-allylic alcohol (Z)-substrate L r5 J envelope TS Homo-allylic alcohol... 

Q9.6 Homo-allylic alcohols, where the alcohol group is removed one extra carbon from the double bond, also show increased reactivity toward metal catalyzed epoxidations by f-BuOOH.3 Explain why this might be so. 

Substituted 5,5-dimethyltetrahydrofuran 8 is obtained by reaction of homo-allylic alcohol 7 with a catalytic amount of lri(OTf)i (0.1 equiv.) and aldehyde (0.1 equiv.) (Scheme 8.123). When the reaction is conducted with an equimolar amount of aldehyde and catalytic In(OTf)3 (0.1 equiv), compound 9 is formed selectively. A tandem 2-oxonia [3,3]-sigmatropic rearrangement/cyclization mechanism is postulated [166]. 

The Ni-catalyzed coupling is a superior method for the preparation of unsymmetrical 1,5-dienes, an allylic nucleophile being generated from fragmentation of a tertiary homo-allylic alcohol. ... 

Mixtures of epoxides and 3-substituted 2-methyl-4-penten-2-ols react to give homo-allylic alcohols, on treatment with In(OTf)3 (or TfOH). Under the reaction conditions the tertiary alcohols are decomposed to generate allylating agents while the epoxides undergo rearrangement to aldehydes, the transformed species then combine to furnish the observed products. ... 

The preparation of an organoaluminium reagent which, although of undetermined composition, is considered to possess a tin-aluminium bond, and its use in converting allylic phosphonates into homo-allylic alcohols in the presence of a palladium catalyst have been described (Scheme 23). ... 

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