In contrast to earlier reported unsuccessful experiments the Michael addition of prop-2-enal to 2-methylcyclopentane-1,3-dione (1) affords 3-( l-methyl-2,5-dioxocyclopentyl)propanal(3) in 90% yield, if the reaction is carried out in water without a basic catalyst. This aldehyde is converted by an intramolecular aldol reaction to (*)-endo-2-and (f)-exo-2-hydroxy-5-methylbicyclo[3.2.1]octane-6,8-dione (rac-4 and rac-6), both affording ( f )-5-methylcycloheptane-l,4-dione (rac-8) after oxidation to ( f )-5-methylbicyclo(3.2.1]octane-2,6,8-trione (rac-2), hydrolytic ring-opening and decarboxylation. This reaction sequence allows the transformation of the 2-alkylated cyclopentane-1,3-dione 1 into the 5-alkylated cycloheptane-1,4-dione rac-8 in a good overall yield. The pathway of the ringopening process has been determined by an investigation of the reaction intermediates.
Cycloadditions of 6H‐1,3,4‐Oxadiazin‐6‐ones (4,5‐Diaza‐α‐pyrones). 14. Reactions of 6H‐1,3,4‐Oxadiazin‐6‐ones with Norbornene: Non‐catalysed and Catalysed by Trifluoroacetic Acid
In 11 out of 13 non‐catalysed reactions of oxadiazinones 1 with norbornene, γ‐oxoketenes 4 were observed and could be isolated in three cases (4b,d,m). Except for 4m, all γ‐oxoketenes isomerised to enollactones of type 5 on thermolysis. However, 4b furnished the cyclobutene derivative 10 as the major product. No γ‐oxoketenes were detected in the reactions of 1k and 1l, which gave rise to the formation of 5k and the enollactone 19, respectively. The latter was converted into 5l on treatment with trifluoroacetic acid (TFA). Four oxadiazinones 1 were allowed to react with norbornene in the presence of TFA. Three of them (1a,b,l) afforded mixtures of enollactones of type 5 and their diastereomers 12. Heating of 4 in the presence of norbornene led to the formation of the symmetrical δ‐lactones 6. This process was observed to be efficient only where the conversion 4 → 5 is slow (4b) or inoperative (4m). In five cases, the treatment of the components with boron trifluoride etherate proved to be a useful preparative alternative (6a,d,g,h,m). On treatment of 4a with methanol, the pseudoester 7a was formed, whereas 4b gave mixtures of 7b and the esters 8b and 15. Hydrogen chloride converted 4b into the pseudochloride 14, which furnished pseudoester 7b on methanolysis. Reaction of 4b,m with formic acid gave rise to pseudoanhydrides of type 13. From 4b and TFA a mixture of the enollactones 5b and 12b was obtained. Boron trifluoride etherate transformed 4i to enollactone 12i; analogously, 12m resulted on treatment of 4m with trifluoromethanesulfonic acid.
2, 2‐Disubstituted Cyclopentane‐1, 3‐diones. IV. Synthesis of Prochiral Intermediates for the Synthesis of 8‐Methyl‐prostaglandin C2 by Alkylation of 2‐Methyl‐cyclopentane‐1, 3‐dione with 1‐Bromo‐alk‐2‐ynes.
2‐Methyl‐cyclopentane‐1, 3‐dione (1) is preferentially C‐alkylated by 1‐bromo‐alk‐2‐ynes in aqueous sodium hydroxide solution. By this method it is possible to prepare 2,2‐disubstituted‐1, 3‐diones (3–8), which can be converted into prochiral intermediates for 8‐methyl‐PGC2, containing the complete carboxylic side chain.
other 6-membered heterocycles other 6-membered heterocycles (with 3 or more heteroatoms) R 0670
-178Cycloadditions of 6H-1,3,4-Oxadiazin-6-ones (4,5-Diaza-α-pyrones) . Part 13. Diels-Alder Reactions with 6H-1,3,4-Oxadiazin-6-ones as Dienophile. -The title compounds (I) and (IV) react as dienophiles with the dienes ( II) and (V) to afford the products (III) and (VI), respectively. An unexpected tricyclic compound (VIII) is obtained with the oxadiazinone (VII). X-Ray structure analyses establish the identity of (VIb) and ( VIII). -(FEINEIS, E.; SCHWARZ, H.; HEGMANN, J.; CHRISTL, M.; PETERS, E.-M.; PETERS, K.; VON SCHNERING, H. G.; Chem.
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