2H-chromenes

Chromene, 2-morpholino-3-phenyl-synthesis, 3, 750 Chromene, 3-phenyl-2-substituted synthesis, 3, 756 2H-Chromene, 6-acetyl-... 

Knoevenagel condensation, 3, 674 2H-Chromene, 4-alkyl-prototropy, 3, 642 2H-Chromene, 3-bromo-synthesis, 3, 668... 

H-Chromene, 6,7-dimethoxy-2,2-dimethyl-application, 3, 881 2H-Chromene, 2,2-dimethyl-addition reactions, 3, 670 fluorinated... 

H-Chromene, 3-phenyl-2-(2-phenylchroman-3-yl)-synthesis, 3, 756 4H-Chromene, 2,4-diphenyl-synthesis, 3, 763... 

H-Chromene, 2-ethyl-3-phenyl-synthesis, 3, 764 4H-Chromene, 2-phenyl-synthesis, 3, 763 4H-Chromene, 2,4,4-trimethyl-addition reactions, 3, 669 2 H-Chromene-3-carboxamide reduction, 3, 675 2H-Chromene-3-carboxylic acid methyl ester alcoholysis, 3, 668... 

H-Chromene-4-carboxylic acid, 3-hydroxy-7-methoxy-ethyl ester... 

The reaction with nitroethanol in the presence of di-)i-bntylammmonium chloride in refluxing iropentyl acetate gives 2-unsnbsdtnted 3-nitro-2H-chromene in 50% yield. Some 3-nitro-2H-chromenes display efficient optical second harmonic generadon for nonhnear opdcal apphcations. 

On the other hand, refluxing 9 in formic acid for 5 h afforded the N-formyl derivative 11 in high yield. Acetylation of 9 by refluxing in acetic acid, afforded acetic acid N -(2-(7-hydroxy-2-oxo-2H-chromen-4-yl)-acetyl)-hydrazide 12 in good yield. Compound 13 was also obtained by refluxing 9 with 3-(2-bromoacetyl)-4-hydroxy-2H-chromen-2-one in ethanol. Reaction of compound 9 with phenyl isothiocyanate in ethanol at room temperature gave 4-phenyl-1 - (7-hydroxy-2-oxo-2 H-chromen-4-acetyl- )thiosemicarbazide 14. 

Condensation of 9 with ethyl acetoacetate without a solvent gave ethyl 3-(2-(2-(7-hydroxy-2-oxo-2H-chromen-4-yl)-acetyl)hydrazono) butanoate 15 in 48% yield (Scheme 3). 

When 11 was refluxed with equimolar amoimts of 4-trifluoro methy-lanUine or 2,3,4-trifluoro anihne in acetonitrile with a few drops of acetic acid, the compounds (7-hydroxy-2-oxo-2H-chromen-4-yl) acetic acid-... 

N -[(4trifluoromethylphenylimino)methyl]hydrazide 16 and (7-hydroxy-2-oxo-2H-chromen-4-yl)-aceticacide-N -[(2,3,4-trifluorophenylimino)methyl] hydrazide 17 were obtained in good yields (Scheme 4). 

Condensation of the aminochromenes 1039 and 1041 with 2-methyl-l,4-benzoquinone (841) afforded 2-(2,2-dimethyl-2H-chromen-7-ylamino)- (1042) and 2-(2,2-dimethyl-2H-chromen-5-ylamino)-5-methyl-l,4-benzoquinone (1043), along with the corresponding 6-methyl isomers. Finally, reaction of the benzoquinones 1042 and 1043 with stoichiometric amounts of palladium(II) acetate in acetic acid under reflux furnished pyrayaquinone A (175) and B (176) in 78% and 50% yield, respectively (623) (Schemes 5.157 and 5.158). 

Fulgides such as the diphenyl derivative (144), dithienylethylenes (145), certain 2H-pyrans (146) and 2H-chromenes (147) and their respective thio analogues (148) and (149) also exhibit photochromism by valence tautomerism. 

The trivial names flavene (10), isoflavene (11) and flavylium (12) are in widespread use and are retained here. However, these compounds will usually be considered as the phenyl derivatives of 2H-chromene or benzopyrylium rather than in separate sections. 

When some 2H-chromenes (147) are irradiated with UV light in 2-methyl-THF at -75 °C, an intense red colour is produced but this fails to appear when LAH is added to the reaction... 

When 2,2-dimethyl-2H-chromene is irradiated in the presence of a quinone such as phenanthraquinone (180), the latter adds across the chromene 3,4-double bond with the... 

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