1,4-pentadiene 3,3,5,5-tetraphenyl

The di-7r-methane rearrangement has been studied in a sufficient number of cases to develop some of the patterns regarding substituent effects. When the central sf carbon is unsubstituted, the di-7i-methane mechanism becomes less favorable. The case of 1,1,5,5-tetraphenyl-l,4-pentadiene is illustrative. Although one of the products has the expected structure for a product of the di-7t-methane rearrangement, labeling with deuterium proves that an alternative mechanism operates ... 

The photochemistry of l,l,5,5-tetraphenyl-3,3-dimethyl-l,4 pentadiene (1) has been studied in detail by Zimmerman and Mariano.<7) Photolysis of compound (1) gave 1,1-diphenyl-2,2-dimethyl-3-(2,2-diphenylvinyl) cyclopropane ... 

One example53) of these will suffice. Thus, the photochemical reactions interconverting 1, l-dicarbomethoxy-3,3,5,5-tetraphenyl-1,4-pentadiene, 1,1,2,2-tetraphenyl-3-(2, 2 -dicarbomethoxyvinyl)cyclopropane, and 1,1 -dicarbomethoxy-2,2-diphenyl-3-(2, 2 -diphenylvinyl)cyclopropane are of interest in several ways. The singlet processes provide an example typifying the treatment of many of the cases referenced above. 

Scheme 5. Singlet Photochemistry of the Dicarbomethoxy Tetraphenyl Pentadiene and Vinylcyclo-propanes.

Occasionally in photochemistry it is observed that the singlet reacts differently than the triplet. A useful generalization has been developed in our research which deals with this phenomenon 49,53,64). This is seen most readily in terms of the chemistry of l,l,3,3-tetraphenyl-5,5-dicarbomethoxy-l,4-pentadiene in Scheme 6. 

Dehydrohalogenation. Kuhn et dissolved 2,4-dibromo-l, 1,5,5-tetraphenyl-pentadiene-1,4 in DMF, flushed the system with nitrogen, and slowly added methanolic... 

Sensitized Photolysis of Dimethyl 3,3,S,S-Tetraphenyl-l,4-pentadiene-l,l dicarboxylate Typical Procedure ... 

A solution of dimethyl 3,3,5,5-tetraphenyl-l,4-pentadiene-l,l-dicarboxylate (200 mg, 0.41 mmol), acetophenone (8.03 g, 66.9 mmol) in benzene (200 mL) was irradiated for 30 min through Pyrex using a 450-W Hanovia medium-pressure lamp. The solvent was removed under vacuum leaving a yellow oil. The sensitizer was removed by bulb-to-bulb distillation at 30 C/0.015 Torr with dry ice cooling of the receiving bulb. The residue consisted of 202 mg (98%) of colorless crystals. Recrystallization (EtjO/hexane) afforded dimethyl 2,2,3,3-tetraphenylcyclopropylmethylidenemalonate yield 161 mg mp 216-217°C. Concentration and silica gel chromatography (5% EtjO/hexane) of the residue afforded an additional 30 mg of the tetraphenylcyclopropane derivative. Total yield 191 mg (95.6%). 

A crystalline film of 314 mg (0.744 mmol) of l,l,3,3-tetraphenyl-5,5-dicyano-1,4-pentadiene 1 a, deposited by slow evaporation of a 20% ether in hexane solution, was irradiated at 78 °C for 2.5 h through Pyrex. The resulting orange-red solid was subjected to preparative HPLC eluted with 8% ether and 0.5% acetonitrile in hexane to give 227.1 mg (72.3%) of starting diene and 74.8 mg (23.8%) of 2 a as a pale purple-red solid. Recrystallization from ether-hexane yielded 69.7 mg (21.6%) of 2a as a white solid (mp 125-128°C). 

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) ... 

Diphenyl-, [52,53], triphenyl-, [53-57], and tetraphenyl-diazocyclo-pentadienes [56,57] have been prepared from the corresponding cyclo-pentadiene salts by the same method. 

Diphenyl.dibenzo-spiiopyran 19 II61. Vsrbiiidang CaHaC sus a-Oxy-eoxo-s.y.d.s-tetraphenyl-ac.v-pentadien 7 I 454. CaH 0,9. 3 Oxo 5 tmon-2.2.4 triphenyl ... 

When the central sp -carbon of 1,4-diene is unsubstituted, the di-n-methane rearrangement is less favorable. The reaction of l,l,5,5-tetraphenyl-2,4-dideuterio-l,4-pentadiene 50 illustrates the fact [46]. 

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