Benzo Benzopyrans

Fernandes MJG, Gonfalves MST, Costa SPG (2008) Neurotransmitter amino acid - oxo-benzo[/]benzopyran conjugates synthesis and photorelease studies. Tetrahedron 64 11175-11179... 

Chemical Name 4-Hydroxy-a-(4-hydroxy-2-oxo-2H-1-benzopyran-3-yl)-2-oxo-2H-1-benzo-pyran-3-acetic acid ethyl ester... 

PPP calculations reproduce the nitro substituent effect and heterocyclic effect on the /,max. For example, the bathochromic shift by substitution of a nitro group is calculated (ca.20nm). It is in good agreement with the experimental value determined (A,max = 598 nm) in toluene. PPP calculation exactly predicts the bathochromic shift by benzo-annelation of the indoline and benzopyran residues (Table 2). In the neutral quinoid form, the calculated charge densities for the ground and first excited states by PPP... 

In contrast to the benzoannelated nitrogen heterocycles, only a few kinds of benzoannelated systems without nitrogen have been described (Fig. 3.15). Five-mem-bered rings such as benzo[b]furans (336) [184, 461] and hydrobenzo[b]furans (337) (Scheme 3.41) [337, 462, 463] and six-membered rings like 4H-l-benzopyran-4-ones (4-chromones) (338) and 2H-l-benzopyran-2-ones (coumarines) (339) [96, 464, 465] 2,3-dihydro-4H-l-benzopyran-4-ones (chroman-4-ones) (340) [466] and 3,4-dihydro-lH-2-benzopyrans (isochromans) (341) [444] have been reported. 

New rearrangements of 2-imino-2//-l-benzopyran-3-carboxamides under the action of anthranilic acid as an N-nucleophile have been revealed. Depending on the conditions 2-(2-oxo-2//-l-benzopyran-2-yl)-3//-quinazolin-4-ones or 2-oxo-2//-l-benzo-pyran-3-((V-2-carboxyphenyl)carboxamides were found to be the products. 

Dihydro-5,7-dihydroxy-4-oxo-4H-l-benzo- pyran-2-yl)-2,3-dihydroxyphenyl]-5,7-dihydroxy- 2-(4-hydroxyphenyl)-4//-l-benzopyran-4-one 2,3-Dihydro-5 -hydroxyamentoflavone... 

The photocyclodimerization of coumarin (2//-l-benzo[b]pyran-2-one) in direct and sensitized experiments is known to proceed rather inefficiently in the absence of Lewis acids and in better yields in their presence.42,43 In contrast, 2-quinolone (22, X = NH)44 or 1-thiocoumarin (2//-l-benzo[b]thiopyran-2-one 22, X = S)45 afford anti head-to-head dimers 23 on direct irradiation in very good yields. Psoralens (7//-furo[3,2-g][l]benzopyran-7-ones) usually exhibit a behavior similar to that of coumarins.46... 

All of the compounds discussed are based on three molecules 2/f-pyran (1), 4//-pyran (2) and the pyrylium cation (3). Names which have been used for the benzologue (4) of 2//-pyran include 2H- 1-benzopyran, benzo-a-pyran, chrom-3-ene and 2//-chromene. A similar situation exists for the corresponding derivative (5) of 4/f-pyran. The unambiguous and simplest name chromene is used in the present work. The benzologue (6) of pyrylium is known both as benzopyrylium and chromylium the former name is preferred here. Higher benzologues are referred to as naphthopyrans, such as 2H-naphtho[ 1,2-6 jpyran (7), but the names xanthene and xanthylium are used for (8) and (9). 

The simple pyrans are rather unstable compounds and of little biological or industrial significance but some of their benzo derivatives are of considerable interest. Many 2H-1-benzopyrans (chromenes) are found in plants, for example evodionol (126), lapachenole (127), lonchocarpin (128), rottlerine (129) and edulan (130). A few of the constituents of marijuana (hashish) belong to this class, for example cannabinol (131). 

Table 2 does the same for the benzo fused thiins, and again 1H-1- and 2H-2-benzothiopyrans and 10H-thioxanthenes have no counterpart in the benzopyran field. As has been remarked, the picture is further complicated by the variable valency of sulfur which permits the functionalization of the heteroatom of most of the ring systems. Thus,... 

Bcnzo[/)]furan and derivatives, recent advances in chemistry of, Part 1, occurrence and synthesis, 18, 337 Benzo[c]furans, 26, 135 recent advances in the chemistry of, and related compounds, 73, 1 Benzofuroxans, 10, 1 29, 251 2//-l-Benzopyrans (chrom-3-enes), 18, 159 Bcnzofc] pyrylium salts syntheses, reactions, and physical properties, 50, 157 1,2-and 2,1-Benzothiazines and related compounds, 28, 73... 

Six-membered unsaturated oxygen heterocyclic compounds are based on three molecules 2/7-pyran 1,4/7-pyran 2, and the pyrylium ion 3. Based on this, the benzo analog of 2/7-pyran is named 277-1-benzopyran (commonly 2H-chromene) and the benzo analog of 477-pyran is called 4/7-1-benzopyran (commonly 477-chromene). The benzo analog of 3 is known as 1-benzopyrylium 6 (sometimes chromylium). Related naphthyl analogs are exemplified by 2/7-naphtho[l,2,A]pyran 7, the xanthylium ion 8, and xanthene 9. 

Many interesting photochemical reactions are possible with pyran-2-one and its various alkyl and benzo derivatives. For example, irradiation of 2-oxo-2/7-l-benzopyran 4-carbonitrile 170 in the presence of excess 2,3-dimethylbut-3-ene in Ar-degassed benzene provided imino-substituted cyclopenta[c]annelated product 171 (Scheme 19)... 

Analogous reactions have been performed in similar benzo- and naphthopy-rane series [101]. Oxidation of benzopyrane derivatives YIII/174 with chromic acid/acetic acid, chromic acid anhydride/acetic acid anhydride, Jones reagent, or ozone gave only complex mixtures of products. Only raefa-chloroperoxyben-zoic acid in dichloromethane was successful (VIII/175 as naphthoketolactones with n = 4, 5, 6 in 70, 49, and 60% yield). 

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