3.5- dioxo-2,4,6-trimethyl

Dioxo-2, 4, 5 -trimethylcyclohexa-l, 4 -diene)-3,3-dimetbylpropi-onamide (Q). The application of this well-known acid [3-(3, 6 -dioxo-2, 4, 5 -trimethylcyclohexa-l, 4 -diene)-3,3-dimethylpropionic acid] to protection of the amino function for peptide synthesis has been examined. Reduction of the quinone with sodium dithionite causes rapid trimethyl lock -facilitated ring closure with release of the amine. 

Trihydroxypteridine exists predominantly in the dioxo-mono-hydroxy form 191(R = H), its ultraviolet spectrum closely resembling those of both the 1- and the 3-methyl derivatives and that of l,3-dimethyl-7-methoxypteridine-2,4-dione (191, R = Me). These spectra are quite different from those of 8-methyl- (192, R = H) and l,3,8-trimethyl-pteridine-2,4,7-trione (192, R = Me), which are similar to each other and to those of other 8-substituted pteridine-2,4,7-triones. However, the ultraviolet spectrum of 2,4,7-trihydroxypteri-dine does, indeed, show that a small proportion of the trioxo form is present at equilibrium. A somewhat larger proportion of the 6-methyl derivative exists in the trioxo form, although structure 193 predominates. The trioxo form (194) of 2,4,7 trihydroxy-l,3,6-trimethyl-pteridine is the most important tautomer, but the corresponding 6-carboxylic acid exists entirely in the monohydroxy-dioxo form 195. 

Dioxo-l,3-dimethyl-tetrahydro-imidazol- (4-spiro-2) - 4,6,7-trimethyl-1,2,3.4-tetrahydro-chinoxalin ... 

Dioxo-l,7,l l-trimethyl-12-[2-hydroxy-propyl-(2)]-11 -(2-carboxy-vinyl)-6-furyl-(3)- 516... 

CN -(2,4,5-trimethyl-3,6-dioxo-l,4-cyclohexadien-l-yl)benzeneheptanoic acid (+)-/ -enantiomer... 

Ausgehend von l-Acetyl-benzimidazol-5,6-dicarbonsaure-anhydrid isoliert man bei dcr Thermolyse mit Azido-trimethyl-silan ein 1 1-Isomcrengcmisch 1-Acetyl-6,8-dioxo-1,5,6,8-tetrahydro-( 1,3-oxazino[4,5-f benzimidazol )ll-Acetyl-5,7-dioxo-l,5,7 8-tetrahydro-(l,3-oxazino[5,4-f]benzimidazol, das ohne Reini-gung direkt mit Amiden (z. B. Formamidinacetat) umgesetzt werdcn kann540. 

When the above-mentioned ring expansion with diazomethane 74) of trimethyl-dioxo[2.2]metacyclophane 65 (methylation was necessary to increase the inversion barrier to > 130 kJ) was performed in the presence of optically active alcohols at —60 °C, asymmetric induction occurred to an extent of ca. 40% ee (enantiomeric excess as determined by nmr-spectroscopy in the presence of chiral shift reagents)85). (+)-DibutyI tartrate favoured the dextrorotatory diketone 66 ([a]D 160° for the optically pure product) — the isomeric 67 was formed only with 3% ee (—)-ethyl lactate on the other hand led to an excess of (+)-67 ([a]D +240°) but gave (+)-66 with only 10% ee85). 

The photoaddition of the pyran-2-one (330) to ethylene to give the adduct (331) has been employed in a synthesis of grandisol,274 and the cyclobutane derivatives (332 and 333) were obtained on irradiation of the pyran-4-one (334) in 2-methylpropene.275 Photocycloadditions of dehydroacetic acid276 and 2,4-dioxo-3,3-dimethyl-2,3-dihydropyran277 have also been described, and the synthetically useful addition of 2,2,6-trimethyl-1,3-dioxolenone (335) to 2,3-dimethylbut-2-ene has been reported.278... 

Heating either trimethyl 2-methyl-6-ethylidene-2,6-dihydro-l//-pyrido[l,2a]-pyrazine-7,8,9-tricarboxylate or tetramethyl 1,2-dimethyl-2,9a-dihydro-l//-pyrido-[l,2-a]pyrazine-6,7,8,9-tetracarboxylate in dilute HC1 gave dimethyl 2-methyl-7-propionyl-l,6-dioxo-2,6-dihydro-l//-pyrido[l,2-a]pyrazine-8,9-dicarboxylates (62JCS1510). 1,12-Dihydroxyper-hydrodibenzo[ac]pyrazine was prepared from l-(2-tetrahydrofuryl)-9-hydroxyperhydropyrido[l,2-a]pyrazine in AC2O saturated with HBr at 95-100°C (61BSF2135). 

Dimeric complexes of the V02 group have single 0x0-bridges giving a [O2V-O-VO2] core such as in [L2V204(/x-O)] (L = 1,4,7-trimethyl-1,4,7-triazacyclononane), or a rare type of dioxo bridge as seen in the compound shown in (10). In this compound, the p-O distances are asymmetric, as indicated, the shorter being about 1.675 A and the other around 2.27 A. 

Triazin 2,4-Dioxo-l,3,5-trimethyl-hexahydro- E4, 1156 (Biuret + CH20)... 

Dioxan 4,6-Dioxo-2,2,5-trimethyl- E14a/I, 717 (Keton + HOOC-CHR COOH)... 

Azeri dill 3-Hydrazinocarbonyl-2-oxo-l, 4,4-trimethyl- El 6b, 538 (aus 3-Diazo-2,4-dioxo-pyrroli-din)... 

H-Purin 2,6-Dioxo-l,3,7-trimethyl-E9b/2, 419 (from natural Prod.) Pyridin 4-Carboxy-3-(3,3-dimethyl-1-triazeno)- E16a, 1197 (Ar—N + Amin)... 

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