Dimethoxy-2,2-dimethylchromene

Aminobenzoyl)-5,7-dimethoxy-2,2-dimethylchromene (0.2 g) was dissolved in EtOH (30 ml) containing water (5 ml) and ammonium chloride (1 g) and Zn mossy (1.5 g) was added in portions and the mixture stirred at room temperature for 5 days. The solution was filtered, evaporated to dryness under reduced pressure and the residue dissolved in EtOAc (25 ml) and worked up in the usual way to give a solid (0.19 g). It crystallised from EtOH with MP 123°-126°C. 

Cyclization of aminodimethylchromenylbenzophenone 6-(2-aminobenzoyl)-5,7-dimethoxy-2,2-dimethylchromene (0.12 g) was dissolved in DMSO (8 ml) and NaH (0.06 g) added, the mixture was stirred for 6 days at room temperature. A further addition of NaH (0.06 g) was made and the solution heated to 50°C for 0.5 h whence it was poured into water, extracted with EtOAc and worked up in the usual way to give a crude mixture (0.11 g components). Separation of this mixture on plate (silica gel benzene EtOAc, 10 4) gave band 1 (Rf 0.45 38 mg) identified as starting material. Band 2 (Rf 0.32 42 mg 43%) which crystallized from ethylacetate as des-N-methylisoacronycine, MP 293°-295°C. Band 3 (Rf 0.10 29 mg, 29%) crystallized from ethyl acetate as des-N-methylacronycine. MP 237°-240°C. 

Chromenes (Phe a-pyran) include encecalin (a phototoxic antimicrobial from various Asteraceae) and the phloroglucinol derivative mallotochromene (cytotoxic and an HIV-1 reverse transcriptase inhibitor). Precocene 1 (7-methoxy-2,2-dimethylchromene) and pre-cocene 2 (6,7-dimethoxy-2,2-dimethylchromene) produced by Ageratum species (Asteraceae) inhibit the production of insect juvenile hormone (JH) as a result of suicidal conversion of these pro-toxins to cytotoxic derivatives by the JH-producing insect cells. 

Precocenes I and II are natural products with a simple chromene structure (7-methoxy- and 6,7-dimethoxy-2,2-dimethylchromene) which were isolated from plant sources and exhibited powerful antijuvenile hormone activities in several types of insects (1). 

Fluoro-l,l-dimethoxy-3-methylbut-2-ene reacts smoothly with a number of phenols. Monohydric phenols containing either electron-releasing or electron-withdrawing substituents afford satisfactory yields of 3-fluoro-2,2-dimethylchromenes. The regioselectivity of this synthon appears to parallel that described above (80JHC1377). 

Prenyl substitution is a conventional derivatization style in stilbenes, exemplified by artoindonesianin N 29 immArtocarpus gomezianus [17]. The prenyl groups in stilbenes cyclize to form new derivatives. 4-Hydroxy-5 -methoxy-6",6"-dimethylpyran[2",3" 3, 4 ]stilbene 30, 3,5 -dimethoxy-4-hydroxy-6",6"-dimethylpyran[2",3" 3, 4 ]stilbene 31, and 3,4,5-trimethoxy-6",6"-dimethylpyran [2",3" 3, 4 ]stilbene 32, with dimethylchromene ring in their structures, have been obtained from Lonchocarpus utilis (Leguminosae) [18]. Furthermore, schweinfurthins A-C 33-35 from the leaves of Macaranga schweinfurthii (Euphorbiaceae) are typical samples of the prenylated stilbenes [19]. 

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