4,6,6‐Trimethyl‐4‐cyclohexen‐1,2,3‐trion, ein Beitrag zur Biogenese von Norcarotinoiden

Abstract

Als reaktive Intermediate der Biogenese von Norcarotinoiden werden Verbindungen mit Cyclohexentrion‐Endgruppen seit zwei Jahrzehnten diskutiert. An der Titelverbindung 1 als Modellsubstanz konnten nun erstmals chemische und spektroskopische Eigenschaften dieser Endgruppe untersucht werden. Das Triketon 1kann sowohl aus dem Cyclohexandion 2 als auch aus dem Cyclopentendion 3 hergestellt werden; es bildet schmierige tiefrote Kristalle, die an der Luft augenblicklich unter Bildung des Hydrats zerfließen.magnified image

The Chemistry of Vicinal Polycarbonyl Compounds

“…An accumulation of spectroscopic evidence has established that hydration occurs at a central carbonyl group of polycarbonyls. This was also established by X-ray crystallography of the hydrate of vinyl-α,β-diketoester 25 37 and by 13 C NMR for the hydrate of 11 . Hydration also occurs at one of the central (C-3) carbonyl groups in vic -pentaketones …”

“…The formation of α-diazo-β-dicarbonyl compounds by the Regitz exchange procedure with tosyl azide, followed by reaction with tert -butyl hypochlorite in the presence of formic acid, has proved, in our hands, to be a superior synthetic method for obtaining highly pure samples of open chain triketones and has also been useful in the synthesis of pentaketones as discussed later. It has been used successfully for preparation of a number of cyclic triones including 9 and 10 ,17a a number of 5- and 6-substituted and 5,6-disubstituted (methyl, methoxy, chloro) indanetriones,17b the cyclohexenetrione 11 , bicyclotriones 12 (R = H, Me), and a new synthesis 20 of cyclopentenetrione ( 13 ), all from the corresponding β-dicarbonyls. Schank and Blattner 21 have described some chemistry of the α-chloro-α-formyl intermediates in this procedure (see section V.E).…”

“…In Tables −7 we have listed the three lowest ionization energies of a number of triketones. In addition to results for the triketones shown in Chart , results are presented for 1,8,8-trimethylbicyclo[3.2.1]octane-2,3,4-trione ( 40 ), dimethyl triketone ( 1g ), diisopropyl triketone ( 1h ), di( tert -butyl)triketone ( 1i ), and 4,6,6-trimethyl-4-cyclohexene-1,2,3-trione ( 11 ) . An extensive study on PE and UV−vis spectra of vinylogous tricarbonyl compounds incorporated in five- and six-membered rings should be mentioned here …”