Dimethyl-3,3-diphenyl-1,1 -cyclopropene

The adduct 32 of diphenylcyclopropenethione to the morpholine enamine of acetophenone reacts with dimethyl acetylenedicarboxylate to yield a mixture of 1,2-diphenyl cyclopropene and dimethyl 4-morpholino-3-phenylthiophene-1,2-dicarboxylate (equation 21)41. 

Dichlorobis(triphenylphosphane)palladium as catalyst leads to mixtures of the tetracyclic homo-cyclotrimer 11 and the tris-cr-homotropone 12 with both 3,3-dimethyl- and 3,3-diphenyl-cyclopropene in relatively low yields. ... 

A useful method for the storage and regeneration of unstable 1 -diarylcyclo-propenes involves the formation of their complexes with (707). Thus, 1,2-diphenyl-cyclopropene or its complex with (707) gives adduct (708) in good yield on heating with 2,5-dimethyl-3,4-diphenylcyclopentadienone. ... 

A wide range of 3,3-disubstituted cyclopropenes, e.g. the dimethyl and diphenyl derivatives, as well as spiro[2.4]hept-l-ene or 6,6-dimethyl-4,8-dioxaspiro[2.5]oct-l-ene, can thus be reacted with a variety of mono- and disubstituted alkynes. Usually, the chemoselectivity of this cy-clocotrimerization reaction is remarkably high. The norcaradiene derivatives initially obtained are in equilibrium with the valence tautomeric cycloheptatrienes. The equilibrium ratio of the valence tautomers is strongly dependent on the position and kind of substituents, especially those in the 7-position of the newly formed norcaradienes and cycloheptatrienes. When one or two phenyl groups are present in this position, only norcaradiene products can be detected by and NMR spectroscopy at room temperature, whereas in the case of methyl substituents, both valence tautomers are formed in almost equal amounts. When cyclic alkynes, such as cyclooctyne, are employed in the reaction, only norcaradienes are formed regardless of the substituents present in the cyclopropene cosubstrate. ... 

Second-order rate constants for the oxidation of cyclopropenes with 3-chloroperoxybenzoic acid in carbon tetrachloride at 0 "C were in the order 1,2-diphenyl- (3.4), 3-methyl-l, 2-diphenyl-(1.24), 3,3-dimethyl-l,2-diphenyl- (0.4), 1,2,3-triphenyleyelopropene (0.122). The rates are somewhat lower than those of the corresponding 3-substituted cyclopentenes. On this scale, the relative rates of reaction of 1,2-diphenylcyclobutene and cyclopentene are 3.3 and 38.8. " ... 

In other related syntheses, pyridazines were formed from l,2-diphenyl-3-(diacylmethylene)cyclopropenes, as shown in Eq. (I)46 or from trans-l,2-dibenzoyl-3,3-diphenylcyclopropane 47 Similarly, pyridazines are formed from hydrazines or semicarbazide and y-trichloromethyl-a,jS-unsaturated ketones.48-52 Pyridazines may also be obtained from 1,2-diketones. The reaction between benzoin and hydrazine was investigated in detail. A complex mixture of various compounds is formed, among them 3,4,5,6-tetraphenylpyridazine in low yield.53 Benzil monohydrazones and analogs when treated with vinyltriphenylphosphonium bromide also give 2,3-dihydropyridazines in moderate yield.54,55 Benzil monohydrazone and related compounds react with dimethyl acetylenedicarboxylate to give a mixture of the corresponding ketazine, bisketazine, and pyridazine 2.56 The last is the main product in the absence of solvent. 

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