Naphthopyran

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... 

The cyclisation of naphthyl propargyl ethers occurs efficiently under microwave irradiation leading to naphthopyrans, but naphthofurans are formed in the presence of base <96JCR(S)338>. The thermal rearrangement of naphthyl 3-trimethylsilylprop-2-ynyl ethers yields the 4-trimethylsilyl derivatives of naphthopyrans <96H(43)751>. 

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. 

The colored form of spironaphthopyran 32 absorbs at A,max of ca. 450 m,70 and the closed spiro form is colorless, which has no absorption band above 400nm. Bulky substituent group is especially important for photochromic sunglass. Introduction of the spiroadamantane or spirobi-cyclo[3.3.1]heptane into the 2-position of naphthopyran increases the resistance to photo-fatigue reaction, since endocyclic double bond induced by 1,7-hydrogen shift in the colored form cannot be formed in 2-adamantyl or 2-bicycloheptanyl group. 

Typical preparation of naphthopyran 32 involves Fries rearrangement of 1-acetoxynaphthalene 30. Condensation of 2-acetyl- 1-naphthol 31 with adamantanone, followed by usual reduction and dehydration gives 32 (Scheme 16).70... 

It is possible to form cyclic ethers from diketones as seen by the cyclic hemike-tal formed by the reduction of 1,5-cyclooctanedione (Eq. 228) and the conversion of 2,5-hexanedione into cis- and /ran.v-2,5 -di me(In Itetrahydrofuran (Eq. 229).392 A naphthopyran can be formed in a similar manner.339... 

Figure 1.8 UV-visible spectra of ORMOSIL-embedded naphthopyrans with different modifying groups show that samples prepared with iBu and Ph groups lead to more significant shifts to the UV compared with samples prepared with the same relative amount of Me groups. (Reproduced from ref. 16,... 

R. Pardo, M. Zayat and D. Levy, The influence of sol-gel processing parameters on the photochromic spectral and dynamic behaviour of a naphthopyran dye in an ormosil coating, J. Mater. Chem., 2005, 15, 703. 

Kinetic Parameters for the Mesityl Site Exchange in Naphthopyrane Derivatives (83, 84, 85)... 

In their closed forms, spiropyran, spiro-oxazine, and some naphthopyrans are chiral about the sp carbon atom that joins their orthogonal or out-of-plane ring... 

The naphthopyran ring-opening reactions have not been as well studied as they have for the spiropyrans and spiro-oxazines. Aubard et al. [75] recently reported that in acetonitrile and hexane, irradiation of CHRl resulted in a broad transient spectrum after 0.8 psec, having three maxima at 360-370 nm, 500 nm, and 650 nm. At 1.8 psec, a well-defined band forms at 425 nm. From 10 to 100 psec, there is little further evolution except for a continued growth in the peak at 425 nm of about 15%. There is also a decrease in the overall bandwidth. The mechanism in Scheme 9 has been proposed, where B2 and B, are isomers of the mero-form. Three isobestic points were identified in the transient spectra at different times, suggesting four transient states. Forming between 0.8 and 1.6 psec, the Bi state was assigned as the cis isomer. This had a spectrum similar to that obtained for Tamai s X transient of the spiro-oxazine NOSH, which was obtained at subpicosecond time scales [26]. 

The opposite direction of spectral shift with solvent polarity is observed for the spiro-oxazine [4] and naphthopyran mero-forms and this is generally accepted to infer a quinoidal HOMO and a zwitterionic LUMO state in their cases. This shift is shown also in Fig. 7b for a naphthopyran TT isomer (CHR2). Of course, H-bonding and other specific interactions will also affect the position of the mero-form spectral maximum. In the case of the substituted BIPS, spiro-oxazine, and CHR2, there is evidence to support their respective assignments to a zwitterionic and quinoidal forms, including x-ray [36,80-85] and NMR [36,55,86-88] data. 

Naphthopyran mero-forms have been studied using H-NMR and NOE studies [78,79]. It has been concluded that there are two isomeric forms that are possible for the mero-form when the terminal methine carbon atom (Cl in Scheme 1 and C42 in Fig. 10) is symmetrically substituted, as shown in Scheme 1. A fourth species has been identified in photo-stationary states of naphthopyran and its mero-forms however, this has not yet been clearly identified. The two main mero-isomers are not in rapid exchange, as two peaks can be clearly identified in the H-NMR spectrum. 

C. Naphthopyran Photochemical Ring Closure and Mero-form Photochemistry... 

Clearly more data are needed to characterize the naphthopyran mero-form photochemistry, as it is not even unambiguously proven that single-photon excitation can bring about the full photo-transformation from the TT isomer to the TC... 

In the case of the single-photon transformation, this is not a general phenomenon and few examples exist. Recently, the crystalline-state photo-transformation of spiropyran [107], naphthopyran [77], and spiro-oxazine [106] chemical systems have been reported. None of these studies, however, give information about transient states except that the study on naphthopyran system described a longer-... 

Naphthopyran rings open rapidly in a few picoseconds to form their mero-form isomers. The interchange between the isomers which form is very slow and sometimes does not even occur unless photo-activated. Photochemical ring closure of the TT mero-isomer does not occur. Instead, it isomerizes to the TC mero-form. Thermal ring closure is rather a slow process showing two clear components due to the two isomeric forms. 

Biphotochromic dyads containing dithienylperfluorocyclopentene and spiropyran (naphthopyran) fragments (05AG(E)5048, 05X3719) are... 

In the reaction of 1-naphthol with 3-nitro-4-fluorobenzalmalononitrile in ethanol, catalyzed by secondary amines, nucleophilic displacement of fluorine competes with pyran ring closure. Application of a tertiary amine (N-methylmorpholine) leads to the selective formation of the corresponding aminochromene (94H(38)399). 2,3-, 1,8-Dihydrooxynaphthalenes 148 and 149 react with 1 or 2 equiv. of aromatic aldehyde 28 and MN 27a to yield naphthopyrans 150 and 151 or dipyrans 152 and 153 (90IJB885, 02RCB2238) (Scheme 53). 

The presence of the enamino moiety in 2-amino-4H-pyrans accoimts for their ability to undergo recyclizations into various pyridones, 1,4-dihy-dropyridines, and 2H-pyrones-2. To some extent, properties of 2-amino-4H-pyrans in reactions with nucleophiles can be compared to those of pyrillium salts (68T5059,80T697) because they also tend to form recyclized products. Reactions proceed in the presence of bases or acids. Naphthopyrans 133 form 2-alkoxypyridines 261 on the action of sodium alcoholates or ethanolic NaOH (79M115) (Scheme 101). 

There are five main classes of compounds which can approach these ideal requirements spiropyrans, specifically spiroindolinobenzopyrans, spironaphthoxazines, naphthopyrans, fulgides and diarylethenes. 

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