2-Phenyl-l-benzopyrylium

When 2-phenyl-l-benzopyrylium salts are treated with sodium azide, 2-azido-l-benzopyrans... 

Much more work has been done on 1-benzopyryliums than on 2-benzopyryliums, because of their relevance to the flavylium (2-phenyl-l-benzopyrylium) nucleus, which occurs widely in the anthocyanins, and much of that work has been conducted on flavylium itself. As with pyrylium salts, benzopyrylium salts usually add nucleophiles at the carbon adjacent to the oxygen. 

Coumarin 13 (27/ -l-benzopyran-2-one), the 1-benzopyrylium ion 14 and the flavylium ion 15 (2-phenyl-l-benzopyrylium ion) derived from flavane (2-phenyl 2i/-chromene) are important derivatives of 277-chromene. They are discussed in chapters 6.7 and 6.8. 

Phenyl-l-benzopyrylium salts (flavylium salts) are important natural products (WillstAtter 1913). Numerous red, blue and violet pigments of blossoms and leaves are derived from the 3,5,7-trihydroxy-2-phenyl-l-benzopyrylium system 5 which has additional OH functions on the 2-phenyl substituent ... 

Benzopyrylium salts (chromylium salts) are colored and possess long-wave UV/VIS maxima at 385 nm. A bathochromic shift is observed in the presence of a 2-phenyl substituent, that is, for 2-phenyl-l-benzopyrylium ions (flavylium ions). H NMR data (cf pyrylium ion, p. 298) show the influence of the positively charged oxygen, which reduces the electron density on C-2 and C-4 5 = 9.75 (2-H), 8.40 (3-H), and 8.75 (4-H) (CF3COOD). This effect is even more pronounced with two benzannulations thus, the dibenzo[b,e]pyrylium ion (xanthyHum ion) shows shifts at 5 = 10.18 (9-H) and 165.1 (C-9) (CF3COOD). 

I Q I 2-Phenyl-l-benzopyrylium salts (flavylium salts) are important natural products... 

The color of anthocyanidin is pH dependent The cyanidin system occurs at pH 3 as a red 2-phenyl-l-benzopyrylium ion 6 at pH = 8, deprotonation leads to the quinonoidal violet colored base 7. In a stronger basic medium (pH = 11), it is converted into the blue anion 8, which forms complexes with A1 or Fe ions. [55]. 

Bromopyrogallol red, B-00574 Butyltriphenylphosphonium(l -I-), B-00640 4-Carboxy-6,7-dihydroxy-2-phenyl-l-benzopyrylium(l-I-) Chloride, in C-00029... 

No simple examples are known of electrophilic or radical substitution of either heterocyclic or homocyclic rings of benzopyrylium salts flavylium (2-phenyl-1-benzopyrylium) and l-phenyl-2-benzopyrylium salts nitrate in the substituted benzene ring. Having said this, the cyclisation of coumarin-4-propanoic acid may represent Friedel-Crafts type intramolecular attack on the carbonyl-O-protonated form, i.e. on a 2-hydroxy-1-benzopyrylium system, at C-3.9... 

No simple examples are known of electrophilic or radical substitution of either heterocycUc or homocyclic rings of benzopyrylium salts flavyhum and l-phenyl-2-benzopyrylium salts nitrate in the substituent... 

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