Heterocyclics benzopyrans

H-I-benzopyrans in, 3, 665 biosynthesis, 3, 877 Mass spectrometry in biosynthesis methodology, 1, 86 heterocyclic compounds reviews, 1, 77... 

The l-imino-lff-2-benzopyran (13) ring opens on treatment with nitrogen nucleophiles. Different modes of recyclisation are possible and (13) is therefore a source of a variety of -heterocycles <96AJC485>. 

Over the years, many spiropyran structures have been prepared. The pyran component consists of benzopyran or naphthopyran and the heterocyclic part consists of indoline, benzothiazoline, benzoxazoline, benzoselen-azoline, phenanthridine, acridine, quinoline, benzopyran, naphthopyran, xanthene, benzodithiole, benzoxathiole, and saturated heterocyclic rings such as pyrolidine and thiazolidine. 

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... 

Reviews of saturated oxygen heterocycles <00JCS(P1)1291>, routes to 2,2-dimethyl-2H-[l]benzopyrans <00H(53)1193> and pyranonaphthoquinone antibiotics <00T1937>, HIV-1 active Calophyllum coumarins <00H(53)453> and of the application of (3-halovinylaldehydes in heterocyclic synthesis <00H(53)941> have appeared. 

The ancient Egyptians used the plantAmmi majus, which contains methoxsalen (sometimes called 8-methoxypsoralen, based on a now obsolete method of naming fused heterocycles indexed in Chemical Abstracts under furo[3,2-g][l]benzopyran-7-one, 9-methoxy-, 249), in combination with sunbathing to... 

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. 

Application of an organocatalytic domino Michael addition/intramolecular aldol condensation to the preparation of a series of important heterocycles has recently received much attention [158] with methods being disclosed for the preparation of benzopyrans [159-161], thiochromenes [162-164] and dihydroquinolidines [165, 166]. The reports all use similar conditions and the independent discovery of each of these reactions shows the robust nature of the central concept. A generalised catalytic cycle which defines the principles of these reports is outlined in Fig. 10. Formation of iminium ion 102 is followed by an intermolecular Michael addition of an oxygen, sulfur or nitrogen based nucleophile (103) to give an intermediate... 

Pyrano-fused heterocycles, namely pyrano[3,2-f]quinoline-2,5(6//)-diones, pyrano[3,2-f]benzopyran-2,5(6//)-dione, and pyrano[3,2-f]pyridine-2,5(67T)-diones, have been efficiently prepared by the condensation of 4-hydroxy-2-(l//)-quinolines, 4-hydroxycoumarin, or 4-hydroxy-(17/)-pyridone with a-acetyl-y-butyrolactone or the sodium salt of a-formyl-y-butyro-lactone in the presence of ammonium acetate <1999JHC467>. 

In complex heterocyclic compounds, the terms coumarano, couma-rono, coumarino are therefore rejected, although they allow a shortening of the occasionally somewhat cumbersome and forbidding Chemical Abstracts nomenclature thus, coumestrol (4) will not be called the dihydroxy derivative of coumarono[3,2-c]coumarin,7 but 3,9-dihydroxy-6 -benzofuro[3,2-c][ l]benzopyran-6-one. 

Simpler names for compounds of type 4 (mentioned in the guiding index of Chemical Abstracts) will be used in this survey the fundamental heterocycle 6f/-benzofuro[3,2-c][l]benzopyran-6-one is called cou-mestan.8 Coumestrol (4) becomes 3,9-dihydroxycoumestan. Another derivative of the same family, waedelolactone,9 is 3-methoxy-l,8,9-trihydroxycoumestan. In this connection, it would be advisable, for natural compounds of botanical origin, to put the corresponding chemical name in brackets. 

Examples of polycyclic compounds with several heterocyclic rings include aflatoxin B (48)153 (2,3,6aa,9aa-tetrahydro-4-methoxycyclo-penta[c]furo[3, 2 4,5]furo[2,3-A][l]benzopyran-l,l 1-dione) which is... 

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. 

The reactivity of 47/-benzopyran-4-ones in Diels-Alder reactions is well documented <1987T3075>, and recently high asymmetric induction has been achieved in the reaction of 3-alkoxycarbonyl-substituted chromones with chiral auxiliaries and Danishefsky s diene <1991JOC2058>. It should be noted that 3-formylchromones can react as heterodienes in the stereoselective inverse electron Diels-Alder reaction with enol ethers <1994T11755> to provide a route to pyrano[4,3-A][l]benzopyrans a heterocyclic nucleus which occurs naturally in the fungal metabolite fulvic acid <1984CC1565>. The thermal Diels-Alder reaction of 477-pyran-4-one 405 in the presence of an excess of Danishefsky s diene 404 provided cycloadduct 406 (Equation 32) <1996H(43)745>. 

Niwa, M., Ito, J., Terashima, K. and Aqil, M. (1994), Garcipyran, a novel 6-aryl-1,2-benzopyran derivative from Carcinia kola. Heterocycles 38(8), 1927-1932. 

The first method is perhaps the most common, and is exemplified by the condensation shown in Scheme 3 of a 2-alkyl heterocyclic quaternary salt or the corresponding methylene base with a 2-hydroxy unsaturated aldehyde grouping (which usually is part of an aromatic ring, as in salicylaldehyde). These intermediates have given a broad assortment of spiropyran classes. The ready availability of 1.2.3.3.-tetraalkyl-3/f-indoleninium salts and salicylaldehydes has led to a large number of spiro-(2i/-l-benzopyran-2,2 -indolines) [this name will be used in preference to the correct T,3 -dihydrospiro(2//-l-bcnzopyran-2,2 -(2 //(-indole)]. A common acronym for this class, BIPS, will be used in this chapter as both singular and plural. 

M. A. GaTbershtam and N. P. Samoilova, Synthesis of l,3-dimethyl-3-phenylspiro[indoline-2,2 -(2 H- 1 -benzopyran)]s and an investigation of the electronic absorption spectra of their merocyanine forms, Chem. Heterocycl. Cpds., 1973, 1098-1100. 

Morpholino-li/-2-benzopyran-l-one (208) adds aromatic aldehydes in hot acetic acid or acetonitrile to form dihydro-4-morpholinocarbonyl-l/7-2-benzopyran-l-ones 209 as mixtures of cis- and trans-isomers. The process is formally an ene reaction in which an acyl group is transferred (equation 88). Analogous reactions with imines, phenyl isocyanate, nitrosobenzene, arenediazonium salts and carbon disulphide lead to a variety of heterocycles (Scheme 7)110. 

Annelatlon reactions. The ketenimine 1 acts chemically as a vinyl phosphonate activated by the cumulated imino group and is useful as an annelation reagent for the synthesis of heterocyclic compounds. As such it condenses with the sodium salt of salicylaldehyde (2) to afford the benzopyrane in 3 in 52% yield. Similarly, the pyrrolizine 5 is available from the sodium salt of 2-formylpyrrole in 51% yield. ... 

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