Cyclohexenyl ketones

Despite the fact that the electrochemical oxidation of most of the nonconjugated dienes generally does not give products which result from interaction of the double bonds with one another, the anodic oxidation l-acetoxy-l,6-heptadienes gives intramolecularly cyclized products, that is, the cyclohexenyl ketones (equation 15)13. The cyclization takes place through the electrophilic attack of the cation generated from enol ester moiety to the double bond. 

Coordination with heteroatoms is not an absolute prerequisite for efficacy in directional control. Thus, the stereochemistry observed in the epoxidation of alkoxy-substituted cyclohexenyl ketones 21 has been explained on the basis of a Felkin-Ahn transition... 

Thiochromans and thiochroman 1,1-dioxides are readily prepared from the corresponding thiochroman-4-one by catalytic hydrogenation in acetic acid/perchloric acid or via the Wolff-Kishner and Clemensen methods. Thermal decomposition of 21 produced thiochroman in 85% yield. Thiochroman and isothiochroman occur in petroleum, and the completely saturated analog of the former (1-thiadecalin) was obtained from propenyl 1-cyclohexenyl ketones in the presence of hydrogen sulfide and sodium acetate in ethanol. 

Cyclization of certain cyclohexenyl ketones with phenylphosphine affords decahydrophosphinolin-4-ones, tor example, ketone (20) yields 1,2-diphenyldecahydrophosphinolin--4-one (21). Also prepared by this method are 1-phenyl- and 2--methyl-1-phenyl-decahydrophosphinolin-4-ones. All have been converted into their 1-oxides, -sulphides, and -selenides (Yu. G. Bosyakov al, zh. obshch. Khim., 1983, 53, 1050). 

Modified Darzens reaction. The original Darzens synthesis of u./3-unxaturated ketones3 involved the addition of acid chlorides to cyclohexenes in the presence of aluminum chloride or stannic chloride followed by dehydrohalogenation. For example, the addition of acetyl chloride to cyclohexene affords l-acetyl-2-chlorocyclohexane, which on dehydrohalogenation (dimethylaniline) gives methyl cyclohexenyl ketone. 

Methyl cyclohexenyl ketone, 8 Methylcyclopentadiene, 200—201 Methylcyclopentadiene dimer, 200... 

We studied the hydrogenation of acetophenone, where a great deal of side-reactions and production of intermediaries take place in a three-phase reactor, with liquid batch and gas continuously fed, at constant pressure and temperature. The catalyst is Rhodium (3%) over activated carbon. The solvent is Cyclohexane. Samples are taken at different instants and analysed by gas chromatography. The species for which measures are available are acetophenone, AC, phenyl-ethanol, PE, methyl-cyclohexyl-ketone, ethyl-benzene, EB, ethyl-cyclohexane, cyclohexenyl-ethanol, CNE, methyl-cyclohexenyl-ketone and cyclo-hexyl-ethanol, CE. 

A novel photocyclization of the aryl cyclohexenyl ketone (86) to the tricyclic compound (87), a potential precursor for gibberellins, has been reported (Scheme 28)/ Closely related cyclizations to give benzannelated five-membered heterocycles have been investigated. A recent example in the nitrogen series involved the photocyclization of the N-arylenamine (88) to the heterocyclic derivative (89), which is a model for the synthesis of Aspidosperma alkaloids (Scheme 29). ... 

The conformationally locked racemic enamine, 4-(4-rOT-butyl-1-cyclohexenyl)morpholine, reacts with (l-nitroethenyl)benzene to give a mixture of diastereomeric 1,2-oxazine 2-oxides 1 and 2 (ratio 1/2 75 25). Whether these arise via an ionic or a cycloaddition mechanism is unclear. Hydrolysis of 1 and 2 with dilute acid gave a 80 20 mixture of trans- and cis-ketones, 3 and 414. 

In a total synthesis of inhibitors of this kind, the following methods have so far been employed successfully (a) reaction of a cyclohexenyl halide with an amine, (b) coupling of an amine with an epoxide, and (c) condensation of an amine with ketone and reduction of the resulting Schiff base (reductive alkylation of an amino sugar). 

The l-[(l-alkyl-2-phenyl-2-cyclohexenyl)carbonyl]-2-methoxymethylpyrrolidines 4 can also be transformed into cyclohexadienyl ketones 5 with simultaneous removal of the auxiliary during hydrolytic workup29. 

Under comparable conditions the submitters found that the corresponding dihydropyran derivatives were similarly obtained by the condensation of acrolein with methyl vinyl ether in 80-81% yield, with ethyl vinyl ether (77-85% yield), with w-butyl vinyl ether (82% yield), with ethyl isopropenyl ether (50% yield), and with w-butyl cyclohexenyl ether (40% yield). Other <, /3-un-saturated carbonyl compounds that have thus been condensed with ethyl vinyl ether are crotonaldehyde (87% yield), meth-acrolein (40% yield), a-ethyh/3-n-propylacrolein (54% yield), cinnamaldehyde (60% yield), /3-furylacrolein (85% yield), methyl vinyl ketone (50% yield), benzalacetone (75% yield), and benzal-acetophenone (74% yield). 

However, the ratios of the unsaturated materials to the saturated materials and of the ketones to the alcohols (Table I) indicate that the yields of unsaturated materials are higher than those of saturated products, especially cyclohexenol. [The excess alcohol might come from 2ROO - 2RO- + 02 however, its importance in the gas phase is unknown.] It was suggested from the above that some cyclohexenol and possibly cyclo-hexenone may be formed from cyclohexenyl hydroperoxide which is produced from chain reactions initiated by the cyclohexyl peroxy radical and cyclohexenyl peroxy radical as shown below. 

Fig. 97. Solvent retained by nitrocellulose films (50/i thickness) after exposure to air at 25°C (Baelz [48]). I—Cyclohexenyl acetate, II—methyl cyclohexanone, III—diacetone alcohol, IV—cyclohexanone, V—cellosolve acetate, VI—amyl acetate-ethyl alcohol I 1, VII—amyl acetate, VIII— methyl cellosolve acetate, IX—amyl acetate-toluene 1 1, X—butyl acetate-ethyl alcohol 1 1, XI—butyl acetate, XII—cellosolve, XIII—methyl-ethyl ketone, XIV—cellosolve-toluene 1 1, XV—methyl cellosolve, XVI—ethyl acetate, XVII—acetone.

When cyclohexene is mixed with anhydrous triflic acid under a high pressure of carbon monoxide (120 atm) followed by the addition of benzene, cyclohexyl phenyl ketone and the isomeric cyclohexenyl cyclohexyl ketones are obtained with little isomerization of the initially formed cyclohexyl cation 22 to methylcyclopentyl cation 23 (Scheme 5.46).422... 

The presence of cyclohexenyl cation intermediates was firmly established by the observation of carbocation rearrangement during the solvolysis of 25, in which an initially generated bent vinyl cation 26 with sp2 hybridization rearranges to a more stable linear vinyl cation 27 with sp hybridization [Eq. (16)]. The ratio of the rearranged to the unrearranged ketones depends on the nature of solvents used and changed from 14 86 (27a 26a) in 60% aqueous ethanol to 46 54 in the less nucleophilic 2,2,2-trifluoroethanol. 

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