Naphtho pyran synthesis

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

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. 

Bloxham, J., Dell, C.P., Smith, C.W. 1994. Preparation of some new benzylidenemalononitrUes by an SNAr reaction—Application to naphtho[l,2-b]pyran synthesis. Heterocycles 38(2) 399-408. 

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). 

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... 

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

H-Naphtho[2,l-fe]pyrans (1.19) with an amino or alkoxy residues in the 6-position (1.30) show particularly high colourability. The 1-amino- and l-alkoxy-3-hydroxynaphthalenes (1.28 and 129) required for the synthesis of these compounds are prepared from 2-naphthol as illustrated in Figure 1.9. ... 

The analogous principle of heterocyclization was used in the synthesis of naphtho[ c]pyran-2-one 261 from peri-methoxynaphthylacetic acid 260, which was obtained from 8-methoxytetralone (76JA4276). Pyronoan-... 

An idea similar to the previous reaction was applied to the synthesis of 2-functional-substituted naphtho[6c]pyrans 287 from peri-hydroxynaphthaldehydes 286 and a-halogenomethylene-active com-... 

The transformation of chroman-4-ones into (S)-chroman-4-ols by Mortierella isabellina has been applied to naphtho[2,3-b]pyran-4-one to provide a synthesis of naturally occurring (S)-4-hydroxy-lapachone (95CJC1399) and various chroman-4-ones have been enantioselectively reduced by NaBTLt in the presence of optically active Co (II) complexes (95AG(E)2145). 

The synthesis of 3//-naphtho[2,1 -6]pyrans substituted in the 3-position with aryl groups is most easily accomplished by the two-step process outlined in Scheme... 

The synthesis of photochromic compounds from a diarylpropargyl alcohol and a di-P -hydroxynaphthalene (2,3- or 2,6- or 2,7-) yields a dipyran.35 Scheme 9 shows the preparation of a dipyran (21) from 2,6-dihydroxynaphthalene (20). The photochromic properties of these compounds are quite similar to those of a 3,3-diary 1-3/ -naphtho[2,l-A]pyran with an oxy-containing heterocycle fused to the naphtho... 

A better method of promoting fade in 2,2-diaryl (and other) 2//-naphtho[1.2-6]pyrans is to introduce a substituent at the 5-position. Such substitution produces steric crowding in the trans quinoidal open form (see Figure 3.14). The steric crowding will result in a destabilization of the colored species and a more rapid conversion (fading) to the colorless ground state. Methyl has been introduced in the 5-position for this purpose.59 The synthesis of the starting material for these 5,6-... 

When the annellated heteroaromatic group is a five-member ring (43, 44), the properties are best described as intermediate between a naphtho and benzopyran. The standard method of synthesis for diaryl naphthopyrans (acid-catalyzed condensation between a diaryl propargyl alcohol and a naphthol, Scheme 8) is reported not to work for heteroaromatic fused phenols. This is true especially in cases where the heteroaromatic phenol contains a (basic) nitrogen. Alternatively, these pyrans can be prepared by the method of Casiraghi69 outlined in Scheme 16. 

The now classical route to 2/7-1 -benzopyrans, cyclisation of aryl propargyl ethers, has been utilised in the synthesis of mollugin <06T8419> and to prepare novel photochromic naphtho[2,l-b]pyrans <06T737>. 

In the synthesis of 2//-naphtho[l,2-i]pyrans from 1-naphthols and l,l-diarylprop-2-yn-l-ols, initial protonation and loss of water from the latter generate an alkynyl carbocation, normally converted to the aryl propargyl ether. However, the concomitant formation of the highly coloured propenylidenenaphthalenones 12, a new class of merocyanine dyes, suggests attack of the allenic form of the cation at the 4-position of the naphthol followed by a 1,7-H shift <03EJ01220>. 

A Suzuki coupling of 2,6-dimethoxyiodobenzene with the dihydroaromatic boron compound 13 forms the basis of a synthesis of the dibenzo[6,t/]pyran ring system <03AG(E)2795> and naphtho[2,3-c]chromenes result from an intramolecular dehydro DA reaction on the diarylalkynes 14 <03SL1524>. 

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