Heterocycles, 1,2-diphenyl-substituted

The relative stability of lithiated thiopyrans seems to depend upon the heterocyclic ring substitution. Thus, a-lithiated 2,6-diphenyl-2//-thiopyran 16 rearranges into the y-lithiated derivative 17 (Scheme 5) (82JOC680), while the reverse transformation occurs on lithiation of 2,6-diphenyl-4-diethylphosphonylthiopyran (80JOC2453). 

Alkynes bearing an adjacent Al-heterocycle, such as 5-ethynyl-1 -methyl-imidazole and 1-propargylbenzotriazole, readily alkylate benzene in the presence of triflic acid to yield diphenyl-substituted products.308 Isomeric ethynylpyridines exhibit distinct differences in reactivity 3-ethynylpyridine exhibits the highest reactivity, whereas 2-ethynylpyridine is the least reactive [Eq. (5.116)]. This is consistent with the involvement of dicationic intermediates as the de facto alkylating agents. Indeed,... 

Figure 1. Representative members of the heterocyclic (het)-substituted platinum 1,2-enedithiolate dual emitters, where L2 = dppm, l,l-bis[diphenyldiphosphino)methane] dppe, l,2-bis[diphenyl diphosphino)ethane] dppp, 1,3-bis[(diphenyldiphosphino)propane].

Nitrosation of l,2,4-triazin-3-amine 2-oxides and subsequent thermolysis of the thus formed diazonium tetrafluoroborate salts 9 affords 3-fluoro-l,2,4-triazine 2-oxides 10 in one example, the 5,6-diphenyl-substituted diazonium tetrafluoroborate 9 (R1 = R2 =- Ph) was isolated as the first stable heterocyclic diazonium salt.98... 

Condensa.tlon, This term covers all processes, not previously iacluded ia other process definitions, where water or hydrogen chloride is eliminated ia a reaction involving the combination of two or more molecules. The important condensation reactions are nitrogen and sulfur heterocycle formation, amide formation from acid chlorides, formation of substituted diphenyl amines, and misceUaneous cyclizations. 

It is also possible to eliminate chloroform from trichloromethyl-substituted heterocycles. For example, A, iV -diphenyl-l,2-diaminoethane reacts with chloral to form l,3-diphenyl-2-(trichloromethyl)imidazolidin which loses one molecule of chloroform upon heating [Eq. (21)]. The l,3-diphenylimidazolidin-2-ylidene... 

Much work in the review period has concerned enantioselective substitution in five-membered heterocyclics. The enantioselective alkylation of some pyrroles by unsaturated 2-acylimidazoles catalysed by the bis(oxazolinyl)pyridine-scandium(in) triflate complex (31) has been reported.39 Compound (33) is formed in 98% yield and 94% ee from the 2-acylimidazole (32) and pyrrole at —40 °C. A series of enantiomer- ically pure aziridin-2-ylmethanols has been tested as catalysts in the alkylation of /V-mclhylpyrrolc and (V-methylindole by ,/l-unsalura(cd aldehydes.40 Enantiomeric excesses of up to 75% were observed for the alkylation of /V-mcthylpyrrole by ( >crotonaldehyde using (2.S ,3.S )-3-mclhylazirin-2-yl(diphenyl)methanol TFA salt as catalyst to form (34). 

There are a series of communications about the formation of dihydroazines by direct reaction of urea-like compounds with synthetic precursors of unsaturated carbonyls—ketones, containing an activated methyl or methylene group. The reaction products formed in this case are usually identical to the heterocycles obtained in reactions of the same binuclephiles with a,(3-unsatu-rated ketones. For example, interaction of 2 equiv of acetophenone 103 with urea under acidic catalysis yielded 6-methyl-4,6-diphenyl-2-oxi- 1,6-dihydro-pyrimidine 106 and two products of the self-condensation of acetophenone— dipnone 104 and 1,3,5-triphenylbenzene 105 [100] (Scheme 3.32). When urea was absent from the reaction mixture or substituted with 1,3-dimethylurea, the only isolated product was dipnon 104. In addition, ketone 104 and urea in a multicomponent reaction form the same pyrimidine derivative 106. All these facts suggest mechanism for the heterocyclization shown in Scheme 3.32. 

Substituted aromatics, including benzene, diphenyl and heterocyclic compounds. 

McDevitt, P. Vittimberga, B. M. The electron transfer reactions of cyano substituted pyri-dines and quinolines with thermally generated diphenyl ketyl. J. Heterocyclic Chem. 1990, 27, 1903-1908. 

The product of reaction between / -tosylazide and substituted 5-aminopyrazoles was observed to be dependent on the extent of the substitution on the heterocyclic ring. Thus l,3-diphenyl-5-aminopyrazole (88) reacted with tosylazide in ethanol, in the presence of NEt3, to afford the pyrazolotriazole (89) (Equation (12)). On the other hand, the 3-phenyl substituted pyrazole (90) reacted under the same conditions to furnish the tetrazene derivative (91) (Equation (13)) <85MI 705-01). 

Carbazole 332, dibenzofuran 333 (Z=0), and dibenzothiophene 333 (Z=S) behave as diphenylamine, diphenyl ether, and diphenyl sulfide, respectively, in their substitution reactions and thus electrophilic substitution occurs at the positions para to the heterocyclic atom, as exemplified for ... 

No hydrolysis is observed when 2,5-diphenyl-1,3,4-oxadiazole, which has a solubility in water of 0.03%, is treated with mineral acids. Neither concentrated HN03 nor treatment with fuming H2S04 at 100° for 4 hours attacks the oxadiazole ring. Similar stability is shown by 2-(o>-styryl)-5-aryl-l, 3,4-oxadiazole.19 On the other hand, the attempt to obtain the free acid by treatment of 2-phenyl-5-p-car-bethoxyphenyl-1,3,4-oxadiazole with caustic soda produces 1 -p-carboxybenzoyl-2-benzoylhydrazine.23 Other aryl-substituted compounds as well as 1,3,4-oxadiazoles substituted in the 2,5-position by various heterocyclic groups are hydrolyzed by mineral acids.26... 

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