Naphthopyran-2-ones

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... 

A facile synthesis of substituted 2-hydroxy-3-dimethylaminopropenoates has been reported. These undergo addition with cyclic 1,3-diketones and (hetero)aromatic hydroxyl compounds to afford either 3-hydroxytetrahydro-277-Tbenzopyran-2-ones, benzo- and naphthopyran-2-ones, and azolo- and azinopyran-2-ones <1998T9799>. 

The atroposelective construction of the 6,6 -biaryl linkage was recognized as the key step in the synthesis of viriditoxin. Although many atroposelective couplings of complex molecules have been completed and have been the subject of many reviews,most of these approaches relied on either proximal stereogenic centers or covalently linked chiral auxiliaries. Our objective was to explore the influence of distal chiral centers on the catalytic oxidative dimerization of naphthopyran-2-ones using vanadium catalysis (Scheme 7). Assembly of naphthopyran-2-ones has been well studied and recently reviewed." The Staunton-Weinreb annulation or the Michael-Dieckmann condensation is ideally suited for the rapid... 

As mentioned in sections 1.2.2.2 and 1.2.3.2, the photochromic reactions of spirobenzopyran and spironaphthoxazines show a marked solvent dependency and this is also the case with benzo and naphthopyrans. Consequently, spectral data collected from the literature is only comparable within any one study or where the same solvent has been used. This accounts for any discrepancies between one set of results and any other one listed in this and related sections of this chapter. The data normally quoted when discussing the properties of photochromic materials relate to the absorption maximum (2. ) of the coloured state, the change in optical density (absorbance) on exposure to the xenon light source (AOD) and the fade rate which is the time in seconds for the AOD to return to half of its equilibrium value. 

The acid-catalyzed cyclization of 3-(2-hydroxyphenyl)propan-l-ones leads to chrom-2-enes. This reaction accounts for the formation of 2,4-diphenylchrom-2-ene from the reaction of phenylmagnesium bromide on coumarin. The organometallic reagent ring-opens the coumarin to the ketone which cyclizes to the chromene on boiling with acetic acid (Scheme 26) (63T839). In a similar manner, various benzocoumarins afford propanones which cyclize readily in acetic acid to the naphthopyran (70JCS(C)1758). 

The dehydration of ds-chroman-3,4-diols with copper sulfate or p-toluenesulfonic acid gives the chroman-3-one (68BSF4203), whilst pyrolysis of the chlorohydrin (615) yields the naphthopyran-3-one (Scheme 235) (67JCS(C)1472). 

A bioxantracene (-)-ES-242-4 (46) was isolated from the culture broth of Verticillium sp. in 1992 as one of eight antagonists for the 7V-methy 1-D-aspartate (NMDA) receptor (7<5). These novel natural products are reported to inhibit the PH]thienyl cyclohexylpiperidine binding to rat crude synaptic membranes, and therefore, are of potential therapeutic interest for die treatment of neurodegenerative diseases. (-)-ES-242-4 (46) is structurally remarkable having an axially chiral binaphthalene core that is adorned with two pyrans of the same absolute chirality. Our interest in the construction of densely functionalized naphthopyran ring systems, via tandem Michael-Dieckmann reactions, promoted us to attempt the first stereocontrolled total synthesis of (-)-ES-242-4 (46) (19). 

The short and convenient synthesis of novel naphthopyranoquinolines from naphthopyran chloroaldehydes via the Doebner-Miller synthesis was developed in the laboratory of J.K. Ray. The chloroaldehydes were treated with 2.5 equivalents of a substituted aniline in ethanol in the presence of 2N HCI to afford enaminoimine hydrochlorides in good yield. These hydrochloride salts were exposed to heat at a temperature slightly above their melting point, resulting in ring-closure and elimination of one equivalent of arylamine hydrochloride. 

A symmetrically-fused naphthopyran has been synthesised albeit in the low yield of 6.25% from 2-naphthol by way of prior 1-alkylation. Thus 4-hydroxy-3-hydroxymethylbutan-2-one added gradually during 3 hours to 2-naphthol in ethanol at 70°C containing amberlyst-15 and the mixture allowed to stand for 16 hours afforded the compound shown after removal of the resin (ref.71). 

On the other hand, Yang etal. [33] have developed an organocatalyzed enantioselective FC-type addition reaction of 2-naphthol 212 with p,y-unsaturated a-ketoesters 209 using a cinchona alkaloid-derived thiourea catalyst 213 (Scheme 2.30). The resulting product 214 is in rapid equilibrium with the cyclic hemiketal 215, which was dehydrated with a catalytic amount of concentrated H SO in a one-pot fashion, providing the naphthopyran derivatives 216 with moderate to good yields (51-91%) and enantioselectivities (57-90% ee). 

Chiral phosphoric acids 24e and ent-26f have been used recently to promote enantioselective F-C alkylations of indoles with 3-substituted 3-hydroxyisoindolin-1-ones 64 (Scheme 35.14) [32, 67]. Moreover, a,a-dicyanoolefins have also been used in association with 2-naphthols for the synthesis of naphthopyrans in high yields (up to 99%) and good selectivities (up to 90% ee) via hydrogen-bonding thiourea catalysis [68]. 

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