1,2-Dimethyl-5,6,7,8-tetraphenyl

Bis-[hydroxymethyl]-l,l -difluoro- 2721 IJ -Dimethyl- 2770, 282J, 2844 3,3 -Dimethyl- 2700, 2770, 2820, 2844. l,l -Dimethyl-tetraphenyl- 3157, 3172 2,2 -Dimethyl-tetrapheny- 2844 3,3 -Dimethyl-tetraphenyl- 2814, 2844 l,l (or 3,3 7)-Diphenyl-tetrapropyl- 3157 l,l (or 3,3 )-Dipropyl-tctraphenyl- 3157 Hexa-tert.-butyl- 3 Q1, 3157 Hexafcrroccnyl- 3159 Hexakis-[dimethylamino]- 3157 Hexakis-[trifluoromethylJ- 2776 Hexaphcnyl- 2797... 

Silacyclopentadiene, 1,1 -dimethyl-2,3,4,5-tetraphenyl-irradiation, I, 618 structure, I, 617 Silacyclopentadiene, 1-methyl-synthesis, I, 615 Silacyclopentadienes... 

However, the relative stabilities of azepine conformers are highly dependent on the nature of the ring substituents, and some substantial inversion energy barriers have been noted, e.g. dimethyl 2,7-dimethyl-3//-azepine-4,6-dicarboxylate [57.3 kJ - mol-coalescence temperature (Tc) 25 5°C],76 isochalciporone (26)(49.4kJ mol-1 Tc 2 + 1 C),40 and 2,4,6,7-tetraphenyl-3/7-azepine (68.1 kJ mol-1 Tt 80°C).37 Ring-inversion activation energies of similar magnitudes have been determined for 4//-azepines.83 85... 

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 ... 

The Lewis acid-Lewis base interaction outlined in Scheme 43 also explains the formation of alkylrhodium complexes 414 from iodorhodium(III) meso-tetraphenyl-porphyrin 409 and various diazo compounds (Scheme 42)398), It seems reasonable to assume that intermediates 418 or 419 (corresponding to 415 and 417 in Scheme 43) are trapped by an added nucleophile in the reaction with ethyl diazoacetate, and that similar intermediates, by proton loss, give rise to vinylrhodium complexes from ethyl 2-diazopropionate or dimethyl diazosuccinate. As the rhodium porphyrin 409 is also an efficient catalyst for cyclopropanation of olefins with ethyl diazoacetate 87,1°°), stj bene formation from aryl diazomethanes 358 and carbene insertion into aliphatic C—H bonds 287, intermediates 418 or 419 are likely to be part of the mechanistic scheme of these reactions, too. 

The photochemical dissociation of Me2Ge from 7,7-dimethyl-l,4,5,6-tetraphenyl-2,3-benzo-7-germanorbomadiene (14) has been studied by flash photolysis, low-temperature matrix isolation and CIDNP 3H NMR techniques30. The results suggest that a biradical (15) is formed as an intermediate species in the photoreaction. The biradical is initially formed in the singlet state, which undergoes conversion to the triplet state before irreversible decomposition to form Me2Ge and tetraphenylnaphthalene (TPN) (reaction 19). 

Like many other 1,3-dipoles (e.g., nitrile ylides, imines, and oxides) (7), thiocarbonyl ylides undergo head-to-head dimerization to give sterically crowded 1,4-dithianes. The first reported example involves the formation of 2,2,3,3-tetraphenyl-l,4-dithiane (18) from thiobenzophenone (5)-methylide (16) (17,28) (cf. Scheme 5.3). Other (5)-methylides are known to form analogous 1,4-dithianes (e.g., thiofluorenone (5)-methylide yields 172) (17). The (5)-methylides of 4,4-dimethyl-2-phenyl-l,3-thiazole-5(4//)-thione (105) and methyl dithiobenzoate (60,104) dimerize to give compounds 173 and 174, respectively. 

Although 1,10-phenanthroline could not be induced to react with phenyl lithium, 4,7-dimethyl- and 4,7-diphenyl-1,10-phenanthrolines, as expected, afford the 4,7-dimethyl-2,9-diphenyl and 2,4,7,9-tetraphenyl derivatives, respectively.196... 

Silacyclopentadiene, 1,1 -dimethyl-2,3,4,5-tetraphenyl-irradiation, 1, 618 structure, 1, 617 Silacyclopentadiene, 1-methyl-synthesis, 1, 615 Silacyclopentadienes Diels-Alder reactions, 1, 618 reactions, 1, 617-620 reduction, 1, 617 structure, 1, 616 synthesis, 1, 585, 586, 614-616 Silacyclopentane, 1-chloro-nucleophilic displacement, 1, 608 Silacyclopentanes, 1, 605-609 chemical properties, 1, 607-608 synthesis, 1, 605-607... 

Groups of reportedly photochromic systems which deserve further study include (a) disulfoxides (123,124), (b) hydrazones (125-129), (c) osazones (130-133), (d ) semicarbazones (134-143), (e) stilbene derivatives (144), (/) succinic anhydrides (145-148), and (g) various dyes (149,150). A number of individual compounds also remain unclassified as to their mechanism of photochromic activity. These include o-nitro-benzylidine isonicotinic acid hydrazide (151), 2,3-epoxy-2-ethyl-3-phenyl-1-indanone (152), p-diethyl- and p-dimethyl-aminophenyli-minocamphor (153), brucine salts of bromo- and chloro-nitromethionic acid (154), diphenacyldiphenylmethane (155,156), 2,4,4,6-tetraphenyl-1,4,-dihydropyridine (155,156), 2,4,4,6-3,5-dibenzoyltetrahydropyran (155,156), o-nitrobenzylidenedesoxybenzoin (157), p-nitrobenzylidene-desoxybenzoin (157), N-(3-pyridyl)sydnone (158,159), tetrabenzoyl-ethylene (160), and the oxidation product of 2,4,5-triphenylimidazole (161,162). 

Three carbon—carbon initiators are currently available commercially, 2,3-dimethyl-2,3-diphenylbutane [1889-67-4] (1), 3,1 dimethyl 3,1 (llplicnylllrxanc [10192-93-5] (2), and l,l,2,2-tetraphenyl-l,2-bis(trimethylsiloxy)ethane [22341-08-8] (3). 

Recently, the intriguing IEDA adducts 48 of 1-germa-2,3,4,5-tetraphenyl-1,1-dimethyl-2,4-cyclopentadiene (47) with N-methylmaleimide and maleic anhydride were prepared by high-pressure reactions (Scheme 15) [43]. 

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