Cyclohexene reduction

For example, when cyclohexene reduction using (NBu4)5 Na3[Ir(l,5-cod) P2Wi5Nb3062] as catalytic precursor was monitored, an induction period was detected corresponding to the formation of active species. Ir nanoclusters formed in situ were isolated from the reaction solution, characterised and reused as catalyst for the same organic process in the latter case, no induction period was observed [3]. 

Vinyl ethers were reductively cleaved by lithium, sodium or potassium in liquid ammonia especially in the absence of alcohols (except terf-butyl alcohol) A mixture of l-methoxy-1,3- and l-methoxy-l,4-cyclohexadiene gave in this way first methoxycyclohexene and, on further reduction, cyclohexene Reductive cleavage of a-alkoxytetrahydrofurans and pyrans will be discussed in the chapter on acetals (p. 104). 

Kinetic data have been reported for cyclohexene reduction with a 1 6 Cr(acac)3- Bu3Al catalyst in heptane at 30 C, which showed a first-order dependence on catalyst and H2. Hydrogenation rates generally decrease with increasing substitution of the alkene substrate. Similar kinetic results were independently obtained for the Cr(acac)3- Bu3Al catalyst. A proposed mechanism involves alkylation of the metal-halide [equation (a)], hydride formation [equation (b)], followed by reversible insertion of the olefin substrate into the metal-hydride bond [equation (c)], and hydrogenolysis of the resulting metal-alkyl bond [equation (d)]. ... 

Another way to make cyclohexenes is by the partial reduction of benzene rings ( Birch reduction, described in Norman, p.553-557) such as ... 

Isophorone usually contains 2—5% of the isomer P-isophorone [471-01-2] (3,5,5-trimethyl-3-cyclohexen-l-one). The term a-isophorone is sometimes used ia referring to the a,P-unsaturated ketone, whereas P-isophorone connotes the unconjugated derivative. P-lsophorone (bp 186°C) is lower boiling than isophorone and can be converted to isophorone by distilling at reduced pressure ia the presence of -toluenesulfonic acid (188). Isophorone can be converted to P-isophorone by treatment with adipic acid (189) or H on(Ill) acetylacetoate (190). P-lsophorone can also be prepared from 4-bromoisophorone by reduction with chromous acetate (191). P-lsophorone can be used as an iatermediate ia the synthesis of carotenoids (192). 

Conversion of 2-cyano-5,5-dimethyl-3-ethoxy-2-cyclohexene (601) into (602) by hydroxylamine has been accomplished (73MI41604). Reduction of the homocyclic ring in the 3-substituted 2,1-benzisoxazole occurred with H2/Pd-C to give the tetrahydro analogs (equation 65) (74JHC395). 

Other methods for the preparation of cyclohexanecarboxaldehyde include the catalytic hydrogenation of 3-cyclohexene-1-carboxaldehyde, available from the Diels-Alder reaction of butadiene and acrolein, the reduction of cyclohexanecarbonyl chloride by lithium tri-tcrt-butoxy-aluminum hydride,the reduction of iV,A -dimethylcyclohexane-carboxamide with lithium diethoxyaluminum hydride, and the oxidation of the methane-sulfonate of cyclohexylmethanol with dimethyl sulfoxide. The hydrolysis, with simultaneous decarboxylation and rearrangement, of glycidic esters derived from cyclohexanone gives cyclohexanecarboxaldehyde. 

Cyclohexenone has been prepared by dehydrohalogenation of 2-bromocyclohexanone, by the hydrolysis and oxidation of 3-chlorocyclohexene, by the dehydration of a-hydroxycyclohexa- ione, by the oxidation of cyclohexene with chromic acid or hydrogen peroxide in the presence of a vanadium catalyst, by I lie addition of acroleiti to ethyl acetoacctate followed by cycliza-lion, hydroly.sis, and decar])oxylation, by the reduction of N,N-dimelliyliiniline with sodium and ethanol itt liquid ammonia... 

An example of this reaction is the reaction of cyclohexene with t-butyl perbenzoate, which is mediated by Cu(I). " The initial step is the reductive cleavage of the perester. The t-butoxy radical then abstracts hydrogen from cyclohexene to give an allylic radical. The radical is oxidized by Cu(II) to the carbocation, which captures benzoate ion. The net effect is an allylic oxidation. 

It is important to exclude air in all hydrazone-type reductions involving olefins (otherwise, over-reduction occurs due to diimide formation) in the above example, as an added precaution cyclohexene was used as a solvent. 

Johnson and Whitehead have further shown that the reductive elimination of the pyrrolidine group from the pyrrolidine enamine of 2,4-dimethyl-cyclohexanone (16), which involved treating it with a mixture of lithium aluminum hydride and aluminum chloride (9), gave the trans isomer of 3,5-dimethyl-/l -cyclohexene (17) which on subsequent hydrogenation on a platinum catalyst led to the // onr-3,5-dimethylcyclohexane (18). 

The rate of transfer hydrogenation also varies markedly with donor structure. For cyclohexene, 1 -methylcyclohexene, l-methyl-4-isopropyl-cyclohexene,and l-methyl-4-f-butyIcycIohexene as donor in the above hydrogenations, after 1 min the reduction was 11, 78, 99, and 99% complete, respectively (97). 

The cyclodimerization of 1,3-butadiene was carried out in [BMIM][BF4] and [BMIM][PF(3] with an in situ iron catalyst system. The catalyst was prepared by reduction of [Fe2(NO)4Cl2] with metallic zinc in the ionic liquid. At 50 °C, the reaction proceeded in [BMIM][BF4] to give full conversion of 1,3-butadiene, and 4-vinyl-cyclohexene was formed with 100 % selectivity. The observed catalytic activity corresponded to a turnover frequency of at least 1440 h (Scheme 5.2-24). 

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. 

Reduction of aromatic rings with lithium or calcium " in amines (instead of ammonia—called Benkeser reduction) proceeds further and cyclohexenes are obtained. It is thus possible to reduce a benzene ring, by proper choice of reagent, so that one, two, or all three double bonds are reduced. Lithium triethylborohy-dride (LiBEtsH) has also been used, to reduce pyridine derivatives to piperidine derivatives." ... 

The preparation of Pans-1,2-cyclohexanediol by oxidation of cyclohexene with peroxyformic acid and subsequent hydrolysis of the diol monoformate has been described, and other methods for the preparation of both cis- and trans-l,2-cyclohexanediols were cited. Subsequently the trans diol has been prepared by oxidation of cyclohexene with various peroxy acids, with hydrogen peroxide and selenium dioxide, and with iodine and silver acetate by the Prevost reaction. Alternative methods for preparing the trans isomer are hydroboration of various enol derivatives of cyclohexanone and reduction of Pans-2-cyclohexen-l-ol epoxide with lithium aluminum hydride. cis-1,2-Cyclohexanediol has been prepared by cis hydroxylation of cyclohexene with various reagents or catalysts derived from osmium tetroxide, by solvolysis of Pans-2-halocyclohexanol esters in a manner similar to the Woodward-Prevost reaction, by reduction of cis-2-cyclohexen-l-ol epoxide with lithium aluminum hydride, and by oxymercuration of 2-cyclohexen-l-ol with mercury(II) trifluoro-acetate in the presence of ehloral and subsequent reduction. ... 

By studying the NMR spectra of the products, Jensen and co-workers were able to establish that the alkylation of (the presumed) [Co (DMG)2py] in methanol by cyclohexene oxide and by various substituted cyclohexyl bromides and tosylates occurred primarily with inversion of configuration at carbon i.e., by an 8 2 mechanism. A small amount of a second isomer, which must have been formed by another minor pathway, was observed in one case (95). Both the alkylation of [Co (DMG)2py] by asymmetric epoxides 129, 142) and the reduction of epoxides to alcohols by cobalt cyanide complexes 105, 103) show preferential formation of one isomer. In addition, the ratio of ketone to alcohol obtained in the reaction of epoxides with [Co(CN)5H] increases with pH and this has been ascribed to differing reactions with the hydride (reduction to alcohol) and Co(I) (isomerization to ketone) 103) (see also Section VII,C). 

Because of the many examples of such activation of metal powders by TCS 14 only a limited and arbitrary number will be discussed here. The Clemmensen-type reduction of ketones such as cyclohexanone with Zn powder in the presence of TCS 14 affords, via 2082, 2084, and 2085, cyclohexene and, via 2082, O-silylated pinacol 2083 [19, 20]. Ketones such as 5a-cholestan-3-one 2086 are reduced by Zn dust-TCS 14 in TFIF, in ca 65-70% yield, to give 5a-cholest-2-ene 2087 and ca 5% 5a-cholest-3-ene [21] (Scheme 13.8). 

Thermal decarboxylation of 119 provided the cyclohexene derivative 120, which gave compound 121 by lithium aluminum hydride reduction. Hydroboration - oxidation of 121, followed by acetylation, gave carba-sugar derivatives (122 and 123) in equal yields. 

The crucial cyclization of 129 was accomplished by oxidation with pyri-dinium chlorochromate (PCC) and acetylation, providing two cyclohexane derivatives (130 and 131) in the ratio of 10 1. Thermal decarboxylation of 130 resulted in formation of the cyclohexene derivative 132, with concomitant elimination. Reduction of the ester group with diisobutylaluminum hydride converted 132 into 133. Hydroboration-oxidation of 133 gave the carba-sugar derivative 134 as a single product. 

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