Cyclohexene, 1-methylene reactions

Cyclohexene, purification of, 41, 74 reaction with zinc-copper couple and methylene iodide, 41, 73 2-CyclohEXENONE, 40,14 Cydohexylamine, reaction with ethyl formate, 41, 14... 

Melhylenecydobutane-l,2-dicar-boxylic anhydride, 43,27 Methylenecydobutanes by addition of allenes to alkenes, 43, 30 Methylenecyclohexane, 40, 66 Methylene iodide, reaction with zinc-copper couple and cyclohexene, 41, 73... 

Zinc-copper couple, 41, 72 reaction with methylene iodide and cyclohexene, 41, 73... 

The reaction of aryldiazoacetates with cyclohexene is a good example of the influence of steric effects on the chemistry of the donor/acceptor-substituted rhodium carbenoids. The Rh2(reaction with cyclohexene resulted in the formation of a mixture of the cyclopropane and the G-H insertion products. The enantios-electivity of the C-H insertion was high but the diastereoselectivity was very low (Equation (31)). 0 In contrast, the introduction of a silyl group on the cyclohexene, as in 15, totally blocked the cyclopropanation, and, furthermore, added sufficient size differentiation between the two substituents at the methylene site to make the reaction to form 16 proceed with high diastereoselectivity (Equation (32)).90 The allylic C-H insertion is applicable to a wide array of cyclic and acyclic substrates, and even systems capable of achieving high levels of kinetic resolution are known.90... 

Titanium enolates.1 This Fischer carbene converts epoxides into titanium enolates. In the case of cyclohexene oxide, the product is a titanium enolate of cyclohexanone. But the enolates formed by reaction with 1,2-epoxybutane (equation I) or 2,3-epoxy butane differ from those formed from 2-butanone (Equation II). Apparently the reaction with epoxides does not involve rearrangement to the ketone but complexation of the epoxide oxygen to the metal and transfer of hydrogen from the substrate to the methylene group. 

Vinylbuta-1,3-diene produces the 1,2- and 3,4-mono-insertion adducts with dichlorocarbene in a 4 1 ratio [37]. A similar preference in reactivity is observed with 3-methylene-cyclohexenes [90]. 1,2-Dienes react with two equivalents of dichlorocarbene to form spiropentanes [21, 90] (Scheme 7.6). Spiropentanes (50-95%) are also obtained from methylenecyclopropanes [36,106] and by the reaction of electron-deficient alkenes with an excess of chloroform [31] (see Scheme 7.12)... 

Cycloalkenes such as cyclohexene, 1-methylcyclohexene, cyclopentene, and nor-bornene are hydrosilylated with triethylsilane in the presence of aluminum chloride catalyst in methylene chloride at 0 °C or below to afford the corresponding hydrosilylated (triethylsilyl)cycloalkanes in 65-82% yields [Eq. (23)]. The reaction of 1-methylcyclohexene with triethylsilane at —20 °C occurs regio- and stereoselectively to give c/i-l-triethylsilyl-2-methylcyclohexane via a tra x-hydrosilylation pathway. Cycloalkenes having an alkyl group at the double-bonded carbon are more reactive than non-substituted compounds in Lewis acid-catalyzed hydrosilylations. ... 

Alkenes react with dinitrogen pentoxide in chlorinated solvents to give a mixture of /3-nitro-nitrate, vic-dinitro, vic-dinitrate ester and nitroalkene compounds. At temperatures between -30 °C and -10 °C the /3-nitro-nitrate is often the main product. The /3-nitro-nitrates are inherently unstable and readily form the corresponding nitroalkenes." Propylene reacts with dinitrogen pentoxide in methylene chloride between -10 °C and 0°C to form a mixture of l-nitro-2-propanol nitrate (27 %) and isomeric nitropropenes (12 %). The same reaction with cyclohexene is more complicated." ... 

Recently, the successful generation of PCU-8-vinylidenecarbene (4a) via reaction of 8-(dibromo-methylene)-PCU (3) with n-BuLi hs been reported [15]. When this reaction is performed in the presence of an alkene trapping agent (i.e., cyclohexene), a cage-functionalized erro-methylenecyclopropane, 5, is the only product. Compound 5 subsequently was characterized via conversion to the corresponding substituted dichlorospiro(cyclopentane), 6 (Scheme 2) the structure was established unequivocally via single-crystal X-ray structural analysis [15]. 

The Claisen rearrangement of allyl vinyl ethers is a classic method for the stereoselective synthesis of y,J-unsaturated esters. The allylic C-H activation is an alternative way of generating the same products [135]. Reactions with silyl-substituted cyclohexenes 197 demonstrate how the diastereoselectivity in the formation of 198 improves (40% to 88% de) for the C-H insertion reactions as the size of the silyl group increases (TMS to TBDPS) (Tab. 14.14). Indeed, in cases where there is good size differentiation between the two substituents at a methylene site, high diastereo- and enantioselectivity is possible in the C-H activation. 

Two examples of the chain reaction involving the a-methylene radical are the irradiation of acetone in the presence of norbornene,107 and that of cyclohexanone in the presence of cyclohexene.108 106 These reactions predominate so that the other products derived from the photochemical reactions were not initially characterized. 

In 1956, Doering et al. reported that methylene (CH2) inserted into the C H bonds of pentane, 2,3-dimethylbutane, and cyclohexene with no discrimination (other than statistical) between chemically different sites CH2 was classed as the most indiscriminate reagent known in organic chemistry. Doering and Kirmse also demonstrated that the C—H insertion reactions of CH2 in solution were direct, single barrier concerted processes with transition states that could be represented as 27 (Fig. 7.12). In particular, they did not proceed via initial H abstraction to give radical pair intermediates that subsequently recombined. (Triplet carbene C H insertions, however, do follow abstraction-recombination, radical pair mechanisms, as demonstrated in classic experiments of Closs and Closs and Roth (see Chapter 9 in this volume). 

Norcarane has been prepared by the reduction of 7,7-dichlo-ronorcarane with sodium and alcohol,6 and by the light-catalyzed reaction of diazomethane with cyclohexene.6 The reaction of cyclohexene with methylene iodide and zinc-copper couple represents the most convenient preparation of norcarane which is of high purity. 

Trimethylammoniummethylide, (CH3)3N+CIi2, prepared by the reaction PhNa + (CH3)4NBr — (CH3)3N+CH2- + NaBr + C6H6, is believed to decompose into trimethylamine and methylene.36 Evidence for methylene is the formation of norcarane when cyclohexene is present. 

It has been assumed 42 that triplet CH2 does not undergo the insertion reaction with C—H bonds, but there is no firm evidence to support this contention. Reaction of CH2 with isobutene, cis and trans butene-2, and cyclohexene (see Sec. IV-E) under conditions favoring formation of triplet methylene gave relatively higher yields of C=C addition products, but the insertion products were nevertheless present in each case. We believe that reduced yields of the insertion products result from lower methylene energy rather than a fundamental difference in reaction mechanism. 

Direct irradiation of diazoacetophenone in cyclohexene yields much the same product distribution as that obtained through the intermediacy of triplet sensitizers, indicating that the reactant benzoyl-methylene most likely is a triplet.60 A small amount of nonstereospecific addition to the olefin occurs, but the major reaction is allylic hydrogen abstraction to yield acetophenone and dicyclohexenyl. In alcohol... 

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