H-Chromene

The synthesis of 2H-chromenes generally utilizes phenols as starting materials. 

This cyclization is initiated by a (3,3)-sigmatropic reaction of 1 involving the phenyl ring and giving rise to the allene 3. In a concomitant (l,3)-sigmatropic process, 3 is rearranged to the orthoquino-methane 4, whose electrocyclization affords the 2H-chromene 

The 2H-chromene system, especially the 2,2-dimethyl-substituted derivative, is a constituent of numerous natural products, such as evodionol (12) and lapachenol (13), which occur in plants, and precocene I/ll (14), a juvenile hormone antagonist. 

Spiro-2H-chromenes of type 15 show the phenomenon of photochromy on irradiation, the 2H-pyran ring is opened reversibly at the O-C-2-bond in a ring-chain valence tautomerization a colored zwitterionic merocyanine system 16 is formed, which can undergo spontaneous thermal re-cyclization to the spirocompound 15 [28]  

From 2H-pyran-2-one two mono-benzannulated systems are derived, namely 2H-1-benzopyran-2-one (1), known under the trivial name coumarin, and lH-2-benzopyran-l-one (2), known under the trivial name isocoumarin. Both systems are discussed in this chapter. 

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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... 

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. 

H-Chromene-4-carboxylic acid, 3-hydroxy-7-methoxy-ethyl ester reduction, 3, 673 Chromenes... 

Pyrazino[f]quinoxaline Pyrazino[2,3-g]quinoxaline 4H,6H-Pyrano[3,2-g]chromene Pyrido[3,2-g]quinoline 1 H-Cyclopenta[1,2-b 4,3-b ]dipyridine Diazafluorenes... 

H-chromene synthesis from, 3, 767 Indenobenzazepines pharmacological properties, 7, 546 Indenone oxide, 2,3-diphenyl-photochromic compound, 1, 385 Indeno[ 1,2-e][ 1,2,4]triazines synthesis, 3, 434 Indicated hydrogen nomenclature, 1, 33 Indigo, I, 317, 318-319, 4, 370 Baeyer synthesis, 1, 319 colour and constitution, 1, 344-345 molecular structure, 4, 162 photochromic compound, 1, 386 synthesis, 4, 247 Indigoid dyes... 

Reaction of 4-amino-l,2,3,4-tetrahydroquinoline-8-carboxamide and 2H-chromene-3-carbaldehydes in MeOH in the presence of pTsOH H20 at room temperature for 20 min then heating for 2 h afforded racemic... 

Substituted hydrazones 85 and 86 were synthesized by the reaction of the corresponding furo[3,2-h]pyrrole-5-carbohydrazides 83 with 6-substituted-4-oxo-chromene-3 -carbaldehydes 84 andmethyl 2-formylfuro[3,2- ]pyrrole-5-carboxylates 80 under microwave irradiation as well as by the classical method. The beneficial effect of microwave irradiation on these reactions was a shortening of the reaction time and an increase in the yields (Scheme 13) [23],... 

In the presence of a ruthenium catalyst, 3-diazochroman-2,4-dione 716 undergoes insertion into the O-H bond of alcohols to yield 3-alkyloxy-4-hydroxycoumarins 717 (Equation 285) <2002TL3637>. In the presence of a rhodium catalyst, 3-diazochroman-2,4-dione 716 can undergo insertion into the C-H bond of arenes to yield 3-aryl-4-hydroxy-coumarins (Equation 286) <2005SL927>. In the presence of [Rh(OAc)2]2, 3-diazochroman-2,4-dione 716 can react with acyl or benzyl halides to afford to 3-halo-4-substituted coumarins (Equation 287) <2003T9333> and also with terminal alkynes to give a mixture of 477-furo[3,2-f]chromen-4-ones and 4/7-furo[2,3-3]chromen-4-ones (Equation 288) <2001S735>. 

As in pyran above, a chromene-4-H, as well as the 2-H variety herein named is also existent, whose systemic name would be ... 

When salicylaldehyde is heated with a 2-nitrovinylamine (122), 2-amino-3-nitro-2/f-chromenes (123) are formed. A number of cannabichromene-type compounds have been synthesized, in moderate yields, by condensing citral with the 2-lithio-derivative of a 3-methoxyanisole (124 R = H or alkyl). ... 

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