Atrovenetin trimethyl ether

Atrovenetin, (Table 12.1), herqueichrysin are related phenalones (ref. 59) and are unusual in that they both contain a trimethylfurano moiety arising from an prenyl ether since there is no 2-hydroxyl group to form a chromene ring from an adjacent C-prenyl group. Synthetic work (ref.59) has led to members of the group by the Claisen rearrangement. Thus the prenyl ether of the phenalone intermediate in DMF at 100°C directly afforded atrovenetin trimethyl ether. 

However in the same solvent containing potassium carbonate, to avoid cyclisation, from the same phenalenone trimethyl ether, a 2-(1,1-dimethyl)allyl-1,3-diketone resulted. Methylation of this trimethyl ether with diazomethane gave a major and a minor tetramethyl ether. The major product by acidic cyclisation with 4-toluenesulphonic acid and demethylation of the product with hydrogen iodide gave racemic atrovenetin and the minor product led by the same sequence of reactions to racemic demethylherqueichrysin. 

The interrelationships between atrovenetin (1), norherqueinone (2), herqueinone (3), deoxyherqueinone (5), and the naphthalic anhydride (8) are shown in the scheme. X-Ray crystallographic analysis (17) of the ferrichloride salt of the orange trimethyl ether of atrovenetin... 

The substituted naphthalene (available in four steps from 3,4,5-trimethoxybenzaldehyde) reacted with malonic acid and polyphosphoric acid (100°, 15 min) to give the phenalenone (29), which was selectively demethylated to (30) with hydrochloric acid. The demethyl compound formed a dimethylallyl ether (31), which on heating in DMF at 100° gave the yellow trimethyl ether of atrovenetin (16). Demethylation of (16) with pyridine hydrochloride led to the racemic natural product. A more prolonged reaction between (28) and malonic acid in poly-... 

Paul, I. C., and G. A. Sim Fungal Metabolites. III. The Structure of Atrovenetin X-ray Analysis of Atroventin Orange Trimethyl Ether Ferrichloride. J. Chem. Soc. (London) 1097 (1965). 

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