5.5- Dimethyl-2-cyclohexenone

Et2Zn addition to 4,4-dimethyl-2-cyclohexenone and chalcone with 81% ee and 90% ee, respectively. 

In a study of the photoisomerization of 4,4-dimethyl-2-cyclohexenone (8) to 6,6-dimethylbicyclo[3.1.0]-hexane-2-one (9) and 3-isopropyl-2-cyclo-pentenone (10), Chapman and Wampfler48 accounted for the pronounced effect of sensitizer concentration by such a self-quenching mechanism. The phenomenon was exhibited by four ketones with () lowest triplet states but not by benzophenone or acetophenone which have (w, n) triplet states.49... 

From the fact that formation of the two cycloadducts from 4,4-dimethyl-2-cyclohexenone (55) and 1,1-dimethoxyethylene was quenched with different efficiencies by di-f-butylnitroxide, Chapman241 concluded that two triplet states were involved. This paramagnetic quencher is known, however, to deactivate both singlets and triplets. 

Irradiation of 4,4-dimethyl-2-cyclohexenone (Formula 83) in tert-butyl alcohol gives 6,6-dimethylbicyclo[3.1.0]hexan-2-one (Formula 84) in good yield with small amounts of 3-isopropyl-2-cyclopentenone (Formula 85) (46). The 3-isopropyl-2-cyclopentenone is formed by photochemical rearrangement of the bicyclic ketone (Formula 84) (46). 

Photolysis of 2-bromo-4,4-dimethyl-2-cyclohexenone only affords reduction, even in a nucleophilic medium343,344. Apparently, this substrate is structurally not suitable to form a vinyl cation. Formation of vinyl radical-derived products is also the main process for all vinylic halides, if their irradiation is performed in an apolar medium. Such photochemical reductive dehalogenation and especially dechlorination reactions have been extensively studied in the past, not in the least because of their importance as abiotic transformation of persistent polychlorinated environmental pollutants. Examples are the cyclodiene insecticides aldrin and dieldrin, which contain a vicinal dichloroethene chromophore. In recent... 

The anions of chiral chromium aminocarbene complexes bearing a proline residue 7.103 have been used as Michael donors in reactions with 2-cyclo-alkenones at -78°C. After acid treatment, 3-acetaldehydosubstituted cycloal-kanones are obtained. The enantioselectivities are not very high (60 - 70%), except with 4,4-dimethyl-2-cyclohexenone [297]. 

The addition of 4, 4-dimethyl-2-cyclohexenone to 1,1-dimethoxyethylene also involves triplet excited state. In this cycloaddition less stable, highly strained trans-addition product is predominantly formed in comparison to more stable cis-adduct ... 

A convenient synthesis of 3,3-dimethylcyclohexanone, a compound obtained otherwise with difficulty, involves hydrogenolysis of 5,5-dimethyl-l,3-cydohexanedione (55). The reduction is believed to go through 3,3-dimelhyl-cyclohexenone (24). Hydrogenation virtually ceases after absorption of 2 mol of hydrogen. 

Liu H. J., Chew S. Y., Yeh W. L. Facile Selective Diels-Alder Reactions of Chiral 5,5-Dimethyl-4,6-Methano-2-Methoxycarbonyl-2-Cyclohexenone. Application to the Total Synthesis of Qinghaosu. Youji Huaxue 1993 13 314 321 Keywords (-)-/f-pinene, asymmetric synthesis... 

Irradiation of a mixture of dimethyl cyclobutene-1,2-dicarboxylate (372) and 3-methyl-2-cyclohexenone (373) gave the adduct (374), which was then pyrolyzed to give the diene (375). Hydrogenation afforded the keto diester (376). On the other hand, when the compound (374) was reduced by NaBH4, y-lactone (377) was... 

Organobis(cupratesY, spiroannelation.16 1,4-Dilithiobutane, prepared from 1,4-dichlorobutane and lithium in ether at 0°, on reaction with copper thiophenoxide (2 equiv.) forms a biscuprate, formulated as 1 for convenience. This dimetallic reagent adds to 3-halo-5,5-dimethyl-2-cyclohexenones (2) to form the spiro-[4.5]decanone 3 in yields as high as 96%. Cuprates prepared from other Cu(I) sources are less efficient, as is the cuprate prepared from di-Grignard reagents... 

Other methods have been described that produce a-iodoenones in specialized cases. Treatment of 3-benzylamino-5,5-dimethyl-2-cyclohexenone with iodine is reported to produce the 2-iodo derivative (Jirkovsky, I. Can. J. Chem. 1974, 52, 55-65). A Wittig-based approach entails the reaction of iodoketophosphoranes with aldehydes (Gorgues, A. Le Coq, A. Bull. Soc. Chim. Fr. 1976, 125-130). 

A method of synthesis which has been used generally in this series employed a Fischer reaction at an early stage to form the tetrahydrocarbazolone nucleus [59] (Scheme 7.2). We devised a second route employing the Fischer method in which the key intermediate was the cyclohexenone (22) (Scheme 7.3). This was readily prepared by treating the enolate of the methyl enol ether (21) with dimethyl(methylene)ammonium iodide [60] to form the Mannich base which was then condensed with 2-methylimidazole to give (22). 

Figure 6.36 Bifunctionality of cinchona alkaloids (A) and Wynberg s proposal for the transition state of the cinchonidine-catalyzed Michael addition of 4-tert-butylthiophenol to 5,5-dimethyl-2-cyclohexenone (B).

They can be prepared from acyclic compounds. In an industrial process, dimethyl malonate is condensed with 4-alken-3-ones (or a mixture of the respective ketones with 5-chloroalkan-3-ones) to give a substituted 3-hydroxy-2-cyclohexenone. Aromatization, in good yield is achieved by reaction of the hydroxycyclohexenones... 

Ss2 reaction with a,fi-epoxy ketones.6 The enolate 1 of 2,3-epoxycyclohexanone reacts with methyllithium to give, after acidic work-up, 2-methy -2-cyclohexenone (3), the product of SN2 addition. Reaction of 1 with lithium dimethyl cuprate on the other hand results in 6-methyl-2-cyclohexcnonc (2), the product of Sv2 addition. 

A related approach directed toward cyclohexane derivatives affords products without carbon substituents on the rings. Ozonolysis of the 6-deoxyhex-5-enopyranoside derivative 14, followed by silylation, gives the unusual pseudolactone 15 in high yield, and this reacts with lithio dimethyl methylphosphonate to yield the cyclohexenone 18 (Scheme 3),... 

The reaction of 2,2-disubstituted 1,3-cyclohexanediones 1 with dimethyl methanephosphonate in THF in the presence of LDA gives 3-substituted 2-cyclohexenones 2 in moderate to very good yields. 

The cyclohexenone 16 would arise from the enol silyl ether containing the dimethyl acetal 15, which originates from one-step opening of the phenylsulfonylmethyl furanose 14. Thus, the starting material simplifies to commercially available D-ribonic acid y-lactone. 

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