Cyclic enone

Regiocontrolled q- or / -alkenylation and arylation of cyclic enones are possible without protection of the ketone by applying the coupling reaction of the Q- or /3-halo enones 607 and 608 with aryl and alkenylzinc reagents[468,469]. 

Cyclododecene (cis and tians) was similady tiansformed to the cyclic enone, which is an impoitant intermediate in the preparation of perfumary products, such as muscone [541 -91 -3J. 

With other ring sizes, the photochemistry of cyclic enones may take different courses. For cyclopentenones, the principal products result from hydrogen abstraction processes. Irradiation of cyclopentenone in eyclohexane gives a mixture of 2- and 3-cyclohexyleyclopentanone. These products can be formed by intermolecular hydrogen abstraction, followed by recombination of the resulting radicals ... 

Hie examples given in Tab. 7.1 illustrate tlie scope of tlie CufOTf i/(S, R, i j-18-catalyzed 1,4-addition. Witli various RyZri reagents, excellent yields and enantiose-lectivities ate obtained for cyclic enones fexcept for cydopentenone, vide infra) [6, 38, 80]. 

Optically active y-alkoxycyclopentenones have become popular in the diastereoselective synthesis of hms-3,4-disubstituted cyclopentanones. The Michael addition to these cyclic enones catalyzed by sodium ethoxide in ethanol277 or by potassium tm-butoxide278 279 proceeds under kinetic control trans with respect to the y-substituent. 

When the cyclic enone is unsubstituted, but the resulting enolate is quenched with an electrophile under conditions of kinetic control the irons adduct is formed exclusively303. Particularly successful is the sequential Michael addition/enolate alkylation in diastereoselective routes to frans-a,/j-difunctionalized cycloalkanones and lactones304-308. The key steps in the synthesis of methyl ( + )-jasmonate (3)309-310 (syn/anti diastereoselection) and (-)-khushimone (4) (syn/anti and induced diastereoselection) illustrate this sequence311 (see also Section D. 1.1.1.3.). 

For a review of Diels-Alder reactions with cyclic enones, see Fringuelli, E Taticchi, A. Wenkert, E. Org. Prep. Proved. Int., 1990, 22, 131. 

Bentrude et al. [46] developed the 1,4-conjugate addition of silylphosphites to cyclic enones induced by photochemical SET. They showed that high yields... 

The optimal reaction conditions were applied with 59d in the addition of various aryl boronic acids and potassium trifluoroborates to several cyclic and acyclic enones (Fig. 8). Arylboronic acids added to cyclic enones in high yields (89-97%) and with good to excellent selectivities (85-98% ee). Under these conditions, the potassium trifluoroborate reagents reacted at faster rates, but with slightly lower selectivities (83-96% ee). The reactions of acyclic enones with aryl boron reagents gave also excellent yields (83-96%). 

Simple Example Lewis acids, such as AlCl, catalyse the Diels-Alder reaction. Workers used a three-fold excess of butadiene to react with the AlCl complex of 5,6 and 7-membered cyclic enones, e.g, (5), giving excellent yields of eie fused bicyclic ketones (6), Me and H must be cis in (6) as they were aiv in (5). 

ClzHi2O Cyclic enone Tricyclic Ar Synth, int. (20) T200... 

Vaz ADN, S Chakraborty, V Massey (1995) Old yellow enzyme aromatization of cyclic enones and the mechanism of a novel dismutation reaction. Biochemistry 34 4246-4256. 

The enantiomeric reduction of 2-nitro-l-phenylprop-l-ene has been studied in a range of Gram-positive organisms including strains of Rhodococcus rhodochrous (Sakai et al. 1985). The enantiomeric purity of the product depended on the strain used, the length of cultivation, and the maintenance of a low pH that is consistent with the later results of Meah and Massey (2000). It has been shown that an NADPH-linked reduction of a,p-unsaturated nitro compounds may also be accomplished by old yellow enzyme via the flcf-nitro form (Meah and Massey 2000). This is formally analogous to the reduction and dismutation of cyclic enones by the same enzyme (Vaz et al. 1995), and the reductive fission of nitrate esters by an enzyme homologous to the old yellow enzyme from Saccharomyces cerevisiae (Snape et al. 1997). 

Scheme 2.12 Cu-catalysed 1,4-additions of RMgCl to cyclic enones with mercaptoaryloxazoline ligands.

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