2-Cycloheptenone

In the case of cycloheptenone and larger rings, the main initial photoproducts are the -cycloalkenones produced by photoisomerization. In the case of the seven- and eight-membered rings, the double bonds are sufficiently strained that rapid reactions follow. In nonnucleophilic solvents dimerization occurs, whereas in nucleophilic solvents addition occurs. ... 

Bromocyclohept-2-en-l-one (40) should be convertable to cycloheptenone (41) by hydrogenolysis of the bromine atom. Thus the process (34) - (41) provides a general method for conversion of symmetrical cyclohexanones to cycloheptenones. 

Johnson s procedure can be used to prepare A-homo-4a-ene-3-keto steroids or, more generally, any 7-membered ketone having an olefinic linkage. For simple saturated 6-ring ketones, Parham s procedure offers an alternate approach to the preparation of cycloheptenones. 

The acid chlorides of to-(2-thienyl) substituted butyric (122) and valeric acids (123), as well as the corresponding 5-alkyl-2-thienyl-substituted compounds, undergo internal Friedel-Crafts reaction (SnCl4,CS2) at the 3-position in 70-80% yield, to give the corresponding cyclohexenones (124) and cycloheptenones (125). ... 

Posner recently reported a very simple and fast way to activate epoxides towards nucleophilic opening by ketone lithium enolate anions by use of BF3 Et20 (1 equiv.) [73]. The application of this procedure to the nucleophilic opening of propene oxide with the lithium enolate of 2-cycloheptanone, obtained by the conjugate addition of trimethylstannyllithium to 2-cycloheptenone, afforded the stan-... 

The addition of lithium dipropylcuprate-boron trifluoride to 4-methyl-2-cycloheptenone produced a d.r. (trans/cis) of 83 17, and almost the same degree of diastereoselectivity was obtained in the case of 5-methyl-2-cycloheptenone23. However, 6-methyl-2-cycloheptenone gave a d.r. (trans/cis) ratio of 37 6323. 

The addition of the anions of racemic 1-(diphenyl)- and l-(diethoxyphosphinyl)-2-butenes to 2-cyclopentenone or 2-cyclohexenone gives y-l,4-add ucls. () A1 ly 1 systems give exclusively. vy/t-adducts while (Z)-allyl systems give exclusively //-adducts. 2-Cycloheptenone gives diastereomeric mixtures of 1,4-adducts and 1,2-addition products1. 

It is gratifying that the same model holds for the conformationally more flexible cyclohep-tenones. Again, the 4-methyl-2-cycloheptenone led preferentially to the s-compound in the (2-propenyl)siIane addition, based on stereoelectronic grounds. 

The 5-methyI-2-cycloheptenones generated the Irani-product in both systems. Again, steric and stereoelectronic effects work in the same direction27. 

A broad study of aluminum chloride-induced cycloadditions of cyclopente-nones, cyclohexenones and cycloheptenones with 1,3-butadiene (1), isoprene... 

Scheme 2.8 Cu-catalysed addition of w-BuMgCl to cycloheptenone with TADDOL-derived ligands.

The E-isomers of cycloheptenes and cyclohexenes are usually not stable enough to be isolated nevertheless they can be trapped by alcohols, as for cycloheptenone 312) (3.7), or observed spectroscopically as for phenylcyclo-... 

The mechanism for formation of the cycloheptenone is exactly the same as discussed in the book. After a Diels-Alder reaction, the enol ether is hydrolyzed to the ketone by an acid-catalyzed mechanism. 

Eor related studies on 6-amino-cycloheptenones see M. Koiwa, G. P.-J. Hareau, D. Morizono, E. Sato, Tetrahedron Lett. 1999, 40, 4199-4202. 

Selenium dioxide causes both oxidation and dehydrogenation of fused cycloheptenones to give indolotropolone [57LA(608)38], In the cases of furan 4a (54CB1197)and thiophene 4b [55LA(595)203], it effects twofold oxidation, yielding hydroxytropolones 11a and 11b, respectively (Scheme 4) ... 

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