Cyclohexanone, selective allylation

Selective oxidation of allylic alcohols.1 This zircononcene complex when used in catalytic amount can effect an Oppenauer-type oxidation of alcohols, including allylic ones, in the presence of a hydrogen acceptor, usually benzaldehyde or cyclohexanone. This system oxidizes primary alcohols selectively in the presence of secondary ones. Thus primary allylic alcohols are oxidized to the enals with retention of the configuration of the double bond in 75-95% yield. The method is not useful for oxidation of propargylic alcohols. 

Elemental antimony is known to mediate the Barbier-type allylation of aldehydes by allylic halides.35 The active intermediates are believed to be allylic antimony(m) species, which are generated from the antimony(O) and the halides. In fact, allylic dichlorostibanes, produced by metathesis of SbCl3 with the corresponding allylic stannanes, react with benzaldehyde to give homoallyl alcohols, where the C-C bond is constructed with -selectivity (Equation (l)).36 Fluoride salts such as KF, NaF, RbF, and CsF accelerate the Sb-mediated Barbier-type allylation with allyl bromide in aqueous media (Equation (2)).37 In the absence of the fluoride ion, no allylation occurs. Although aromatic and aliphatic aldehydes are allylated in good yields by a combined use of Sb-KF, acetophenone, cyclohexanone, and methyl pyruvate remain untouched. 

The triethylaluminum or triethylborane ate complexes (12) of the (isopropylthio)allyl carbanion react with carbonyl compounds at the a-position (equation 10). In the reactions with carbonyl compounds, very high regioselectivity (for example, butanal 95 5, 3-methylbutanal 99 1, cyclohexanone 92 8 and acetophenone 95 5) was achieved by using the aluminum ate complex. On the other hand, the a-regio-selectivity with ketones decreases if the boron ate complex is used (cyclohexanone 72 28, acetophenone 45 55). It is noteworthy that the stereoselectivity of the a-adduct from an aldehyde is low. Ihesumably the geometry of the double bond in the ate complex (12) is not homogeneous. ... 

The cyclohexanone hydrazones (183e) rearrange similarly (Table 15a). The cis isomers (entries 2 and 4) required elevated temperatures for deprotonation owing to the stereoelectronically disfavored equatorial disposition of the a-proton (H-2). The diastereofacial selectivity of the rearrangement was high in all cases examined but the diastereoselectivity at the allylic center was poor (entries 3-5). 

This experiment describes the lithiation of allyl trimethylsilane and the conversions of the lithio compound with trimethylchlorosilane and cyclohexanone, reactions that proceed with very high y-selectivity. For functionalizations with other electrophiles, e.g., epoxides, alkyl halides, and carbon dioxide, see Ref. [1] and literature cited in this paper. 

Oxidation and Reduction.—Pyridinium chlorochromate adsorbed on alumina has been reported as a selective oxidant cholesterol was converted in high yield into cholest-5-en-3-one. Similar oxidations have been reported with CrOs in Et20-CH2Cl2 in the presence of celite ° and with NaOCl-AcOH. When chromic acid in an acidic medium was used to oxidize steroidal allylic acetates to the corresponding a,/3-unsaturated ketones the quasi-axial acetates were more reactive than their quasi-equatorial epimers. Cholesterol and cholest-4-en-3/8-ol were converted, with Raney nickel and cyclohexanone in toluene, into 5/8-cholestanone in modest yield. 

The 0-atom donor, lutidine-AT-oxide, has been used with Ru(TMP)(0)2 to catalyze the room temperature oxidation of alcohols to the corresponding aldehydes or ketones in -80% . Thus, under Ar, allyl alcohols were oxidized selectively to a,P-unsaturated aldehydes selectively, and PI1CH2OH to PhCHO Ph(CH2)20H was not oxidized. Cyclohexanol and adamantanol gave the corresponding ketones. The related 2,6-Cl2pyNO system, mentioned in the previous section, catalytically oxidizes cyclohexanol to cyclohexanone. ... 

Carbonyl compounds are quantitatively reduced regio- and stereo-selectively by NaBH4 at room temperature in aqueous solutions containing glycosidic amphiphiles such as methyl-p-D-galactoside, dodecanoyl-p-D-maltoside, L-arabinose and sucrose [63]. a,P-Unsaturated ketones give 1,2-reduction to corresponding allylic alcohols and cyclohexanones furnish the thermodynamically more stable alcohol. The observed stereodifferentiation can be attributed to hydrophobic interactions between amphiphilic carbohydrates and lipophilic substrates. 

A review describes the asymmetric epoxidation of allylic alcohols,369 another the role of metal oporphyrins in oxidation reactions.370 jhe TiiOPrMi, catalysed self-epoxidation of allylic peroxides proceeds via an intermolecular mechanism.371 Racemic allyl alcohols can be resolved by asymmetric epoxidation (eq.35).372 a Pd(II)/Mn02/benzoquinone system catalyses the oxidative ring-closure of 1,5-hexadienes (eq.36).373 propenyl phenols are oxidatively degraded to aryl aldehydes and MeCHO in the presence of Co Schiff-base catalysts.374 An Oppenauer-type oxidation with Cp2ZrH2/cyclohexanone converts primary alcohols selectively into aldehydes.375 co macrocycles catalyse the oxidation of aryl liydrazones to diazo compounds in high yields.376 similar Co complexes under CO oxidise primary amines to azo compounds.377 Arene Os complexes in the presence of base convert aldehydes and water slowly into carboxylic acids and H2.378... 

As the aUylated enamine has higher reactivity (i.e., lower ionization potential) the selective mono-aUylation of cyclohexanone required excess (2 equiv.) ketone reagent. Nevertheless 20 equivalents of cyclobutane were necessary for the selective reaction with cyclobutanone and only 2,5-bis-allylated cyclopentanone was obtained, as the second oxidation occurred immediately on the iminium intermediate prior to hydrolysis with this substrate. The allylation reaction was compatible with alkyl and heteroatom substituents at the P and y positions. When non-symmetrical heteroatom containing substrates were used, C(4) allylation occurred selectively in high yields (70-86%) and in high ee (80-99%) (Figure 39.2). 

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