2-Cyclohexenone trans isomer

XXXVIII) is obtained from cyclohexanone (n = 1) the product is primarily the cis isomer. A mixture of the cis and trans products is obtained from cyclohep-tanone (n = 2), whereas from the cyclooctanone (n = 3) the product is primarily the trans isomer (XXXIX). Similar effects are also observed in the hydrogenation of the bicyclic systems (XL) in acidic media, as shown in Table V (50). The hydrogenation of 3,5-disubstituted cyclohexenones (XLI) gives exclusively cis-disubstituted cyclohexanones regardless of reaction conditions (22). 

The photocycloaddition of 1-alkenylboranes in cyclohexane provided m-fused head-to-head adducts for 2-cyclopen-tenone and a mixture of cis- and trans-isomer for 2-cyclohexenone (Equation (71)).397... 

One of the components of the aroma of tea is theaspirone (96).No less than five syntheses of this compound have been published (Scheme One of the more interesting reactions is the selective reduction of the acyclic enone (95) leaving the cyclohexenone intact.The cis and trans isomers... 

In any conformationally mobile a,j3-unsaturated ketone that exists as a mixture of s-cis and s-trans isomers at room temperature there will usually be one conformer that will be energetically more favourable. It is therefore to be expected that a decrease in temperature will increase the population of the favoured isomer, and this may be detectable in the benzene-induced solvent shifts of the substituents. Variable-temperature studies in toluene-c g solution of some model fixed s-m and s-trans a,) -unsaturated ketones have been carried out and the data for 3-methyl-cyclohexenone (33) are fairly typical (see Fig. 4 the chemical shift is given in c./sec. at 100 Me./sec. relative to internal TMS). 

The use of oxazole-alkene Diels-Alder cycloadditions to form biologically relevant molecules has recently been applied to the synthesis of isoindoles, useful intermediates for the preparation of substance P antagonists. Thus 5-ethoxy-4-methyloxazole 8 reacted with 4,4-dimethyl-2-cyclopentenone 78 in refluxing benzene in the presence of catalytic zinc bromide to give the (l//)-cyclopenta(c)-pyrrole 80 as a separable 3 1 mixture of cis and trans isomers in 53% yield (Fig. 3.22). The reaction is presumed to proceed via the intermediacy of cycloadduct 79. When cyclohexenone 81 was used as the dienophile, the product was the hydro-(l//)-isoindole 82, obtained via dehydroformylation of the cycloadduct, in 85% yield after only 30 min in refluxing benzene. 

The first asymmetric procedure consists of the addition of R2Zn to a mixture of aldehyde and enone in the presence of the chiral copper catalyst (Scheme 7.14) [38, 52]. For instance, the tandem addition of Me2Zn and propanal to 2-cyclohexenone in the presence of 1.2 mol% chiral catalyst (S, R, R)-1S gave, after oxidation of the alcohol 51, the diketone 52 in 81% yield and with an ee of 97%. The formation of erythro and threo isomers is due to poor stereocontrol in the aldol step. A variety of trans-2,3-disubstituted cyclohexanones are obtained in this regioselective and enantioselective three-component organozinc reagent coupling. 

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