Dimedone enaminone

Condensation of primary dimedone enaminones with formaldehyde according to Greenhill and coworkers26,27 give, in neutral medium, methylenbisenaminones, whereas acidic conditions produce spirocompounds. Structure A is given by Greenhill27 for the spiro-product, but structure B (equation 20) also seems reasonable. Modern spectroscopic methods should be used to solve this problem. Similar products are obtained in the Mannich reaction of enaminones derived from indan-l,3-dione33. 

The Mannich reaction of enaminones was examined intensively. Enamines derived from dimedone are aminoalkylated in the -position in good yield if the nitrogen is unsubstituted or monosubstituted31,34. Primary amines and formaldehyde react with enaminones to yield tetrahydropyrimidines34 (equation 21). A similar reaction is observed for acyclic enaminones. With primary amines and formaldehyde, tetrahydropyrimidines are formed35 (equation 22). 

With the morpholino enaminone derived from dimedone the oxidized enamine adduct shown in Scheme 41 could be isolated. 

The enaminone 239, prepared from dimedone and ammonia, is converted into the spiro compound 240 by the action of formaldehyde in dilute hydrochloric acid, but under neutral conditions the di(enaminone) 241 is formed. The latter cyclizes under the influence of hydrochloric acid to a derivative 242 of decahydroacridine dione (equation 101)124... 

The enaminone 404, prepared from o-phenylenediamine and dimedone, affords 1,4-diazepines 405 on treatment with aldehydes (equation 167)196. 

Reaction of 2-acetyl-5,5-dimethyl-cyclohexandione 169 (R1 = Ac) with enaminone 31 (R = H) in refluxing ethanol afforded the phenanthridine-1,7-dione 383 (90KGS66). Alternatively, 383 was obtained from bicyclic tetraketone 384 on treatment with ammonia (83ZOR2322). The 9,10-dihydrophenanthridine 386 rather than the rearranged product 387 was obtained by thermolysis of 2-arylaminomethylene derivative 385, obtained from the reaction of dimedone and arylamine in the presence of triethyl orthoformate and polyphosphoric acid (77S723, 96JHC905) (Scheme 79). 

When enaminones 100 (R = H, Me) are allowed to react with carbon disulfide in NaOH/DMF followed by treatment with 10% hydrochloric acid, the dithiolane 101 is obtained. Similarly, 103 is available in 40% yield from the enaminone 102. The enaminone 104 (R = H) derived from dimedone fails to give the corresponding dithiolane 105 reaction is only successful when the aromatic ring carries an amino group (104, R = NH2), Scheme 28 (90H1 91JHC1245). 

Refluxing the enaminones 149 with diphenylcyclopropenone in toluene gives first the adducts 150, which rearrange to the pyrrolones 151 in good yields. Scheme 39. Enaminones derived from dimedone give the corresponding spiro pyrrolones, but in low yields (80JOC5340). 

It has been reported that dimedone and 1,3-cyclohexanedione react with hydrazones to give enaminone intermediates, which are converted in situ to pyrazoles (73CB450),... 

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