3.5.5- Trimethyl-l,2-cyclohexanedione

Acidification of the residual aqueous solution followed by extraction with ether permits the isolation of about 1 g. of the enol form of 3,5,5-trimethyl-l,2-cyclohexanedione (see Note 3). 

Iodosobenzene diacetate in the presence of base converts cyclohexanone into a-hydroxycyclohcxanonc in 80% yield. A related reaction is the conversion of iso-phorone into the enol of 3,5,5-trimethyl-l,2-cyclohexanedione (equation IH). This... 

If the organic layer is dried over magnesium sulfate and fractionally distilled at this point, both 2,4,4-trimethylcyclo-pentanone and 2-formyl-2,4,4-trimethylcyclopentanone, b.p. 49-50° (2 mm.), By 1.4495, may be isolated. The pot residue from this distillation contains a small amount of the enol form of 3,5,5-trimethyl-l,2-cyclohexanedione which crystallizes from petroleum ether as white needles, m.p. 92-93°. 

Intermolecular de Mayo reactions are efficient for cyclic 1,3-diketones such as dimedone (5,5-dimethyl-l,3-cyclohexanedione)96,103,104 and acyclic systems such as acetylacetone93-95. Unsymmetrical acyclic /l-diketones, such as 1-phenyl-1,3-butanedione98 can enolize in two directions, however, reaction normally occurs preferentially from a single enol form. Examples of alkene photocycloaddition to trapped ends of /(-dicarbonyl compounds (e.g., 2,2-dimethyl-3(2/f)-furanone and 2,2.6-trimethyl-4/f-l,3-dioxin-4-one) are given in Table 1 (entries 26, 27) and Table 2 (entry 35) 10°. If the enol is stabilized by derivatization (e.g., acetylated dimedone 3-acetoxy-5,5-dimethyl-2-cyclohexenone), the primary cyclobutane photoproducts can be isolated96. 

Dimethyl-l,3-cyclohexanedione (dimidone, 145) and ethyl 2-(/7-tolylhydra-zono)acetoacetate (146) gave ethyl 4,7,7-trimethyl-5-oxo-l-p-tolyl-l,5,6,7-tetrahydro-3-cinnohnecarboxylate (147) (neat AcONEU, 170°C, 30 min 80%) " the same substrate (145) and benzil monohydrazone (148) gave 7,7-dimethyl-3,4-diphenyl-6,7-dihydro-5(l//)-cinnolinone (149) (or tauto-... 

C6 all-frflrt5-Retinylidene dimedone [70424-15-6] (all- )-2-[3,7-Dimethyl-9-(2,6,6-trimethyl-1-cyclohexen-1 -yl)-2,4,6,8-nonatetraenylidene]-5,5-dimethyl-l, 3-cyclohexanedione... 

Phenylimino-4-oxo-l,6,6-trimethyl-l,3,4,5,6,7-hexahydro-2,l-benzisothiazole refluxed 3 hrs. in HCl-ethanol-water -> 1,1-dimethyl-4-(2-benzothiazolyl)-3,5-cyclohexanedione monomethylimide. Y 94%. Also with NaOH s. J. Goerdeler and U.Keuser, B. 97, 2209 (1964). 

In 2002, Itoh and Kanemasa found that the combined use of both amine and chiral Lewis acid (R,R)-DBFOX-Ph complex of Ni(II) can be an active catalyst for enantioselective Michael addition of nitromethane or malononitrile to unsaturated carbonyl compounds [37a,b]. Recently, they have reported a new enol ketone synthesis through the reactions between cyclic 1,3-dicarbonyl donors and a,p-unsaturated carbonyl acceptors under the double catalytic activation conditions (10mol% each) of Ni(11)-perchlorate hexahydrate and (2,2,6,6-tetramethylpiperidine (TMP) (114))(Scheme 16.33) [38a,b]. Thus, 1,3-cyclohexanedione (112) is allowed to react with 4-bromo-l-crotonoyl-3,5-dimethylpyrazole (113), in THF at room temperature in the presence of both catalytic amounts to give 4,7,7-trimethyl-3,4,5,6,7,8-hexahy-drobenzopyran-2(H),5-diones (115) in good yields along with high enantioselectivity up to 99% ee. 

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