Carbonyl substituted cyclohexenes

Electronic effects can also influence the ease of double bond hydrogenation. Compounds such as A cyclohexenecarboxaldehyde (4) and other 3-carbonyl substituted cyclohexenes, such as 5 and 6, are more difficult to hydrogenate than the non-carbonyl containing materials. This decrease in activity has been attributed to an interaction between the carbonyl carbon and the 7t cloud of the double bond, shown by 7, which has been termed a supra-annular effect.7-"... 

The intermolecular Diels-Alder reaction between the dibromoenone (111) and dienes (112) provides access to bicyclo[5.4.0]undecane systems (113) that are common core structures of many natural products (Scheme 32).118 The alio-threonine-derived O-(/ -biphenyl carbonyl oxy)-/i-phenyloxazaborolidi none catalyses the enan-tioselective Diels-Alder reaction of acyclic enones with dienes.119 The reversal of facial selectivity in the Diels-Alder cycloaddition of a semicyclic diene with a bro-moenone was induced by the presence of the bromo substituent in the dienophile.120 Mixed Lewis acid catalyst (AlBr3/AIMe3) catalyses the Diels-Alder reaction of hindered silyloxydienes with substituted enones to produce highly substituted cyclohexenes.121 Chiral /V-enoyl sultams have been used as chiral auxiliaries in the asymmetric Diels-Alder reactions with cyclopentadiene.122... 

But the best El eliminations of all are with tertiary alcohols. The alcohols can be made using the methods of Chapter 9 nucleophilic attack by an organometallic on a carbonyl compound. Nucleophilic addition, followed by El elimination, is the best way of making this substituted cyclohexene, for example. Note that the the proton required in the first step is recovered in the last—the reaction requires only catalytic amounts of acid. 

The data given in Table 2 show that the ester bonds in the COLs III and IV as well as the cyclic imide group in XIII considerably decrease the epoxidation rate in comparison with non-substituted cyclohexene as well as with cyclohexene compounds bearing substituents other than ester groups. It may be due to the electron acceptor character of the ester group. The presence of two groups (IV) and two carbonyls in the cychc imide XIII decreases the reaction rate even more. 

Vitamin A is an example of a biologically important compound for which a number of cis—trans isomers are possible. There are four carbon-carbon double bonds in the chain of carbon atoms bonded to the substituted cyclohexene ring, and each has the potential for cis-trans isomerism. Thus, 2 = 16 cis—trans isomers are possible for this structural formula. Vitamin A is the all trans isomer. The enzyme-catalyzed oxidation of vitamin A converts the primary hydroxyl group to a carbonyl group of an aldehyde to give retinal, the biologically active form of the vitamin ... 

It can be seen that primary and secondary R02 radicals disproportionate with the participation of the a-C—H bond. This explains why the substitution of D in the a-position for H retards the recombination of R02 [/tn//tD =1.9 for ethylbenzene, h/ d = 2.1 for styrene, and h/ d=1-37 for diphenylmethane [179]). Because of this, R02 radicals of unsaturated compounds with a double bond in the a-position to the peroxyl free valence disproportionate more rapidly than structurally analogous aliphatic peroxyl radicals (at 300 K, 2kt = 2x 107 and 3.8 x 106 L mol-1 s-1 for R02 radicals of cyclohexene and cyclohexane, respectively [180]). Among the products of secondary peroxyl radicals disproportionation, carbonyl compound and alcohol were found in a ratio of 1 1 at room temperature (in experiments with ethylbenzene [181], tetralin [103], and cyclohexane [182-184],... 

This procedure illustrates a general method for the preparation of rearranged allylic amines from allylic alcohols.2,3 The method is experimentally simple and has been used to prepare a variety of allylic prim-, sec-, and tert-carbonyl amines as illustrated in Table I. The only limitation encountered so far is a competing ionic elimination reaction which becomes important for tri-chloroacetimidic esters of 3-substituted-2-cyclohexen-l-ols.3 4 The rearrangement is formulated as a concerted [3,3]-sigmatropic rearrangement on the basis of its stereo- and regiospecificity3,5 which are... 

The complex 8W (R = Me) can also be used in a stoichiometric metathesis sequence to effect the ring closure of unsaturated ketones so as to form 1-substituted cyclopentenes, cyclohexenes and cycloheptenes in good yield, e.g. equation 24. The C=C bond reacts first to give [W]=CH(CH2)3C0(CH2)0(CH2)3Ph, which then undergoes an internal carbonyl-olefination reaction13. 

Woerpel and Calad tested for the formation of the silacarbonyl ylide by interrogating the behavior of the electrophilic silver silylenoid intermediate 115 toward a,(3-unsaturated carbonyl compounds (Scheme 7.37).82 They hypothesized that formation of silacarbonyl ylide 131 might trigger a 6jt-electrocyclization to form oxasilacyclopentene 132. As anticipated, exposure of cyclohexene silacyclopropane 58 to substoichiometric amounts of silver trifluoroacetate in the presence of a,(3-unsaturated carbonyl compounds 130 produced oxasilacyclopentenes 132. The reaction tolerated a substitution at the a and/or (3 position and was general for both esters and ketones. 

Annelation. The Pd(0) complex in combination with N(C2H5)3 (1.5-2 equiv.) effects cyclic carbopalladation of substrates such as 1, a cyclohexene substituted by a y-iodoallyl electrophile group and activated by a carbonyl group,... 

Phosphine-substituted rhodium carbonyl clusters, such as [Rh6(CO)ioL6] (L = (PPh3)6, [P(OMe)3]6, or [(-)-DI0P]3), are good catalyst precursors for cyclohexene hydrogenation.- - ... 

Flowers et al. have dealt with the thermal gas-phase reactions of methyl-oxirane, other methyl-substituted oxiranes, and ethyloxirane. The kinetics of the processes have been compared. Pyrolysis of these compounds is a first-order, homogeneous, nonradical process the reaction rate is not affected by radical scavengers. A biradical mechanism holds. The thermochemical behavior of cyclopentene oxide and cyclohexene oxide is similar. The primary products are the corresponding carbonyl compounds and unsaturated alcohols. Two mechanistic possibilities have been discussed they are obtained from a common biradical intermediate or the alcohol is formed directly from the oxirane in a concerted manner. Thermolysis of spirooxiranes leads to ketone derivatives via biradicals with homolytic bond cleavage (Eqs. 376, 377). ... 

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