1.2- Diphenyl-3- cyclopropene

Diphenylcyclopropene thione (156) was prepared11S-12°) from 3,3-dichloro-1,2-diphenyl cyclopropene (154) by reaction with thioacetic acid, since transformation of the carbonyl function of diphenyl cyclopropenone with P4S10121 was complicated by ring expansion to the trithione 155122 In a useful recent thioketone synthesis123) 156 was obtained directly from diphenyl cyclopropenone in a quantitative yield by simultaneous treatment with HC1 and H2S. 

Das 2,3-Diphenyl-cyclopropen-2-yl-methyl-Kation aus (48) wurde im Hinblick auf seine Eigenschaften als kombiniertes Homoallyl- und Cyclo-propylmethyl-Kation von Breslow und Mitarbeitem untersucht (l03). 

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. ... 

The major product in the photorearrangement of 3-substituted 2-methyl-1,3-diphenyl-cyclopropenes was an indene produced by cleavage of the ring bond which is methyl- rather than phenyl-substituted, apparently by funneling of the excited state of the cyclopropene to the energy surface of the higher lying carbene triplet. ... 

Diphenylcyclopropenylium ion 1 was reduced with sodium borohydride to give 1,2-diphenyl-cyclopropene (2). However, unless the inverse addition method was applied, 2 was rapidly attacked by the unchanged cyclopropenylium ion, resulting in cleavage of the three-membered ring and recyclization to afford 1,2,4,5-tetraphenylbenzene (3) as the final product in quantitative yield. 

Besonders schnell verlaufen die Dimerisierungen von III und VII zu VI und 3-(r-l,c-2-c-3-Triphenyl-cydopropyl)-l,2,3-triphenyl-cyclopropen (Verh. 60 40) sowic VIII, wenn mit Thioxanthon (ET = 65 kcal/Mol) in Benzol sensibilisiert wird2. Entsprechend erhalt man aus 1,2-Diphenyl-cyclopropen bei -78° in Dichlormethan 1,2,4,6-Tetraphenyl-mUi-tricyclo[3.1.0.02 ]hexan. Dieses liefert schon beim Erwarmen auf 13° 1,2,4,5-Tetraphenyl-cyclohexadie.n-ll,4) (F 257-258,5°)2 ... 

Various substituted diphenyl cyclopropenes react smoothly with PTAD to give good yields of the corresponding bicyclic compounds. Examples, together with the proposed mechanism, are shown in Scheme 72 <90JOC2478>. 

A formal [3 + 3]-cyclodimerization of cyclopropenes via ring-opening (Eq. 36) to give six-membered carbocycles has only been observed in the case of 1,2-diphenyl-cyclopropene (Eq. 43). 

Allylcyclopropenes undergo a degenerate 3,3-sigmatropic shift and an intramolecular 2-1-2 cycloaddition. Padwa showed that 3-ally 1-3-methyl-1,2-diphenyl-cyclopropene equilibrates with 3-allyl-2-methyl-l,3-diphenyl.cyclopropene and 6-methyl-l,2-diphenyltricyclo[3.1.1.0 ]hexane at 150°C (Scheme 7.79). " ... 

In an attempt to determine whether peracid oxidation of cyclopropenes to enones proceeds by ct- or ic-bond oxidation, Friedrich and Fiato compared the second-order rate constant for allylically substituted cyclopropenes and cyclopentenes. The results (Table 1) indicate rather small allylic substitution effects in the cyclopentenes, but larger rate reductions in the cyclopropenes. The magnitude of the effect is not in line with an epoxidation-type transition state and may be more consistent with o attack, but insufficient background data are available to allow firm conclusions from these results. A comparison of oxidation rates of 1,2-diphenyl-cyclopropene, -cyclobutene, and -cyclopentene yielded data which were much more consistent with oxabicyclobutane formation, as did an examination of substituent effects at the vinylic positions in cyclopropene. ... 

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. ... 

Irradiation of a mixture of 9,10-dicyanoanthracene and methyl 1,2-diphenyl-cyclopropene-3-carboxylate in benzene gives rise to an emitting exciplex which, in turn, leads to the cycloadduct (150 exo-COjMe). However, in polar media (MeCN) the adduct produced is the sterically least favoured form (150 cndo-COjMe) and its structure has been confirmed by X-ray methods. The production of endo-isomer in this way is believed to proceed via enolization of the cyclopropene radical cation to the planar cyclopropenyl radical cation which, in turn, gives a planar cycloaddition product. Protonation from the direction of least steric interference gives the observed product. This route gains support from the incorporation of deuterium label... 

Metal vinylidenes easily form by isomerization of metal-alkynecomplexes, which is important for instance in alkyne polymerization by the metathesis mechanism. Synthesis of Grubbs ruthenium vinylidene complexes [Ru(PR3)2Cl2(=C=CHPh)] originally proceeded by reaction of the ruthenium precursor with diphenyl-cyclopropene, but a more modern method leading to the parent vinylidene complex involves benzylidene exchange for the vinylidene in the metathesis with 1,3-butadiene ... 

Whereas the Rh2(OAc)4-catalyzed addition of diazoalkanes to propargyl alcohols readily gives the insertion of the carbene into the 0-H bond, with only a small amoimt of cyclopropenation of the resulting propargylic ether [54] the 2-diazopropane 59 reacts at 0 °C with l,l-diphenyl-2-propyn-l-ol 62a in dichloromethane and exclusively gives, after 10 h of reaction, only the adduct 63a isolated in 75% yield and corresponding to the regioselective 1,3-dipolar cycloaddition of the 2-diazopropane to the alkyne C - C bond (Scheme 15). 

It should be pointed out that there are some methylene cyclopropene derivatives, whose stability is ascribed mainly to inductive effects brought about by strongly electron-withdrawing substituents. Thus, l,2-bis(p-tolyl)-4,4-(bis-trifluoromethyl)-triafulvene (63) synthesized recently by Agranat66 is a perfectly stable molecule with a dipole moment (7.42 D) comparable to that of l,2-diphenyl-4,4-dicyano-triafulvene (64) of the resonance-stabilized type (l)67 (7.9 D). 

The Wittig reaction of diphenyl cyclopropenone with the phosphorane 68 failed to give the methylene cyclopropene instead a hydrocarbon of probable structure 67 was obtained71. ... 

Triafulvene 69 was synthesized by an interesting route starting with diphenyl cyclopropenium cation and lithio ethyl acetate72. Although widely used in calicene chemistry (see later) this reaction principle — like the Wittig reaction — did not find general application in methylene cyclopropene synthesis. 

Selective reduction of the cyclopropenone carbonyl group to a CH2 group has been described for diphenyl cyclopropenone utilizing its protonation product 294 or the diphenyl chloro cyclopropenium cation 292, which yielded 1,2-diphenyl-A1,2-cyclopropene (293) on treatment with trimethylamine borane210 ... 

The photochemical behavior of methylene cyclopropenes is a subject of current investigation170 Previous results with some 4,4-diacyl and 4,4-dicyano triafulvenes indicate that mainly dimerization, but sometimes additional solvent incorporation and hydrogen abstraction occurs. In the case of the photodimer of 1,2-diphenyl-4,4-diacetyl triafulvene (180) the structure 460 can be assigned from spectral evidence ... 

Thus TONE is reported to give with l,2-diphenyl-4-carbethoxy triafulvene (69) the spirocyclohexene 49569 the (2 + 2) cycloadduct of the semicyclic methylene cyclopropene bond to TCNE ... 

---