2//-Naphtho pyrans

This chapter, far from being exhaustive, is aimed at outlining the properties of the radical ions and of the free radicals derived from photochromic compounds independently of whether or not these paramagnetic species are involved in the photochromic process itself. In particular, it will deal with the EPR of dihydro-and dialkyldipyridyl radical cations (viologens) and of the radical anions of a variety of nitro-substituted spirofmdoline-benzopyrans], spiro[indoline-naphtho-pyrans], and spiro[indoline-naphthoxazines] as well as their triphenylgermyloxy nitroxides and with the triplet spectra observed upon irradiation of 2,2,4,4-tetrachloro-1 -keto-1,4-dihydronaphthalene. 

A variety of heterocyclic rings have been incorporated into the benzopyran system either as substituents at the critical sp hybridised centre adjacent to the O heteroatom or around the periphery of the molecule. In a different vein, heterocycles have been fused onto both benzo-and naphtho- pyrans. Aspects of the synthesis of these compounds and the influences of the new heterocyclic moiety on the photochromic properties are discussed. 

Mahajan has described a novel route to macrocyclic ketolactones using a retro-Dieckmann reaction (Scheme 24). Although perhaps not of general applicability, the method appears attractive for the synthesis of the type of molecule shown in the scheme. The same idea of bond fission of polycyclic systems to form macro-lides has been used to prepare ketolactones from 2,3-polymethylene-benzo- and -naphtho-pyrans by oxidative cleavage (Scheme 25). 

Figure 40.6 Structures and processes involved in the photochromism of the different photo-chromic dyes (diarylethenes, fulgides, azobenzenes, spiropyrans, spirooxazines, and naphtho-pyrans). The colors of the different states of the photochromic dyes are showed.

Lapachenole — see 2H-Naphtho[l,2-6]pyran a-Lapachone, dehydrosynthesis, 3, 751 Large heterocyelic rings anions, 7, 18 aromatieity, 7, 14, 16 basicities, 7, 24 bond angles, 7, 14-16 bond lengths, 7, 14-16 cations, 7, 18... 

H-Naphtho[2,3-h]pyran, 5,10-diacetoxy-2-methyl-oxidation, 3, 670 Naphtho[2,3-c]pyran synthesis, 3, 770... 

Naphtho[ 1,2-h]pyran-4-one, 3,6-diacetyl-2-methyl-deacetylation, 3, 713 Naphtho[ 1,2-h]pyran-4-one, 5,6-dihydro-synthesis, 3, 811... 

Naphtho[2,l -h]pyran-1 -one, 2,3-dihydro-dehydrogenation, 3, 724 halogenation, 3, 731 Naphthopyranones synthesis, 3, 805 Naphthopyran-2-ones, dihydrosynthesis, 3, 802 Naphtho[l, 2-h]pyran-2-ones synthesis, 3, 802 Naphtho[2,1 -h]pyran-3-ones synthesis, 3, 803, 856 Naphtho[2,1 -c]pyran-4-ones synthesis, 3, 831 Naphtho[2,3-c]pyran-l-ones synthesis, 3, 831 Naphthopyrans H NMR, 3, 580 IR spectra, 3, 594 synthesis, 3, 743, 748, 750, 763 UV spectra, 3, 598 Naphthopyrans, dihydrosynthesis, 3, 778, 783 Naphtho[l,2-h]pyran-4-thione, styryl-properties, 3, 708... 

Forskolin (5-[acetyloxy]-3-ethenyldodecahydro-6,10,10b-trihydroxy-3,4a,7,7,10a-penta-methyl-[3R- 3a-4aP, SP, 6P, 6aa,10a, lOaP, 10ba -lFf-naphtho[2,l-b]pyran-l-one) [66575-29-9] M 410.5, m 229-232°, 228-233°. Recrystd from CfiH6-pet ether. It is antihypertensive, positive ionotropic, platelet aggregation inhibitory and adenylate cyclase activating properties [Chem AbstrS9 1978 244150, de Souza et al. Med Res Rev 3 201 1983]. 

Naphthalene-1,8-dicarboxylic add, its nitro-substituted derivatives, and naphthalene-1,4,5,8 tetracarboxylic acid, on treatment with sulfur tetrafluoride at 0 C, undergo dehydration to form quantitatively the corresponding anhydrides [218, 221] Unsubstituted and mononitrated monoanhydndes react further at 200-250 °C to give derivatives of 1,1,3,3-tetrafluoro-l// naphtho[I,8 c,d]pyran Dinitronaphthalene-l,8-di-carboxyhc acid anhydndes and naphthalene 1,4,5,8 tetracarboxylic acid dianhydnde give the respective tetra- and octafluoroethers only in the presence of an excess of anhydrous hydrogen fluoride [221] (equabons 113 and 114)... 

Bei der Reduktion von 4-Alkyl-(naphtho-[2,l-b]-pyryIium)-Salzen mit Natriumbora-nat werdenhauptsachlich 4H-(Naphtho-[2,l-b]-pyrane) gebildet1.2-Benzo-[c]-py-rylium-Salze werden durch Lithiumalanat zu lH-(Benzo-[c]-pyranen) reduziert2. 

Die Bildung cyclischer Ather bei der Reduktion cyclischer Carbonsaure-anhydride mit Lithiumalanat wird der sauren Aufarbeitung zugeschrieben (s. S. 203)1 . In Ausnahmefallen werden auch mit Natriumboranat in Hy-droxyl-Gruppen-freiem Medium cyclische Ather7 erhalten. Wahrend Naphthalin-l,2-dicarbonsaure-anhydrid mit Diboran ausschlieBlich zum I.2-Bis-[hydroxymethyl]-naphthalin (63% d. Th.) reduziert wird, erhalt man aus Naphthalin-1,8-dicarbonsaure-anhydrid nur 111,3H- (Naphtho-[ 1,8a,8-c,d]-pyran) (40% d.Th.) ... 

The regiospeciflc ortholithiation of 3H-naphtho[2,l-fe]pyrans has also been used to advantage in methylteretifolione B synthesis. ... 

Structural studies of 2-amino-4H-naphtho[2,l-fc]pyrans (87JOU369, 02RCB2238) and enantiomerically pure naphtha[l,2-b]pyrans (96JHC27) revealed a similarity in structural properties to those of 8 and 9. 

Single maxima at 225-230 nm characterize 2-amino-4H-naphtho[2,l-b] pyrans (94H(38)399). Tetrahydrochromene 14 shows maxima at 220 and 269 nm (70CJC3064). 

Naphtho[2,l-( ]pyrans 291 with carbon disulfide lead to dithiones 292 (08PS1145), perhaps via a Dimroth rearrangement of possible intermediates 293 (Scheme 122). 

B. 1,3-Dimethyl-6H-benzo[b]naphtho[1,2-d]pyran-6-one (4). Under an argon atmosphere, a 250-mL, oven-dried, round-bottomed flask, equipped with a reflux condenser, is charged with freshly distilled N,N-dimethylacetamide (DMA, 130 mL), 3,5-dimethylphenyl 1-bromo-2-naphthoate (3, 3.24 g, 9.12 mmol), palladium(ll) acetate (205 mg, 0.913 mmol), triphenylphosphine (481 mg, 1.83 mmol), and sodium acetate (1.50 g, 18.3 mmol) (Notes 4 and 5). The orange suspension is degassed three times, placed in a preheated (130°C) oil bath (Note 5), and stirred at 130°C for 12 hr (Note 6). Removal of the solvent at 40°C (0.1 mbar, 0.075 mm) gives a black oily residue, which is Chromatographed (5 x 40 cm column, silica gel 0.063 - 0.2 mm, 170 g, 1 cm of charcoal at the top of the column eluent hexane / diethyl ether 5 1), to yield 2.00 g (80%) of the lactone 4 as a slightly yellow solid. Recrystallization from diethyl ether / hexane delivers 1.63 g (65%) of colorless or pale yellow crystals (Note 7). 

Dimethyl-6H-benzo[b]naphtho[ 1,2-d]pyran-6-one 6H-Benzo[b]naphtho[ 1,2-d]pyran 6-one, 1,3-dimethyl- (13) (138435-72-0)... 

Reactions of propargylic alcohols with 2-naphthol gave the cycloaddition products such as ll-f-naphtho[2,l-fo]pyrans in excellent yields with complete selectivity... 

The photochromic compounds of potential interest, based on the 2//-chromene ring system, are the 2//-benzopyrans (1.18) or the three isomeric naphthopyrans (1.19-1.21). However, 2H-naphtho[2,3-( ]pyrans (1.21) show little or no useful photochromic behaviour and can be discounted from any further discussion. Although R and can be part of a carbocyclic spiro ring, they are more commonly unconnected substituents such as gem dialkyl or aryl groups. 

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