2.2.4.6- Tetraphenyl-2//-pyrans

Some 2//-pyrans are capable of autooxidation.172,372 Thus whereas 2,2,4,6-tetraphenyl-2f/-pyran (310a) was completely inert,372 the condensed... 

As a rule dipyrylenes are characterized by chemical and thermal stability, but under special conditions cleavage of the ethylene bond can be achieved. Thus, on heating with thionyl chloride followed by treatment with water, the tetraphenyl derivative (52c) is converted into 2,6-diphenyl-4l/-pyran-4-one.50,108 Only decomposition products were isolated with the corresponding methoxyphenyl derivative (52d). 

Sauerstoff- oder schwcfcl-haltige sechsgliedrige Eeteroaromaten konnen untcr dem EinfluB von Licht aufgcspalten werden2-7. So entsteht z. B. aus 2,2,4,6-Tetraphenyl-2H-pyran oder -2H-thiopyran 5-Oxo-l,l,3,5-tetraphenyl-pentadien-(l,3) bzw. das entsprechende o-Thiono-1,1,3,5-tetraphenyl-pentadien-(l,3) ... 

Cher ein intermediar auftretendes valenzisomcrcs Lacton wird die Bildung von 1,2,4,7-Tetraphenyl-cycloodatetraen neben p-Terphenyl und Diphenyl-acctylen aus 2-Oxo-4,5-diplienyl-2H-pyran gedeutet3 4 ... 

As briefly mentioned in Section III. A, 2,4,4,6-tetraphenyl-4//-pyran (8a) was chlorinated, brominated, and even nitrated under mild conditions in positions 3 and 5 to appropriate derivatives 12a (X = Y = Cl, Br, N02) (92CCC546). Vilsmeyer-Haack formylations of 6a (89AP617) and 8a... 

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