Diphenyl cyclobutanes

The failure of 3,6-diphenyl-3,4,5,6-tetrahydropyridazine to undergo elimination of nitrogen on irradiation11 has been attributed to facile isomerization to the corresponding hydrazone under slightly acidic conditions. However, photolysis with a Pyrex-filtered high-pressure mercury lamp in the presence of a trace of V, V-diisopropylethylamine gave the stereoisomcric diphenyl-cyclobutanes (cisjirans 1.7 1, 41%) and styrene (54%).12... 

The oxidative photocleavage of l,2-bis(4-methoxyphenyl)cyclobutane is also accelerated in the presence of Mg(C104)2. However, no salt effect was found for 1,2-diphenyl-cyclobutane because the very fast electron back-transfer prevents interaction of the caged ion pair with the added salt (Pac et al. 1987). 

Demgegenfiber dimerisieren einige trisubstituierte Butadiene-(1,3) bei direkter Belichtung in hoher Ausbeute zu einheitlicheren Produktcn. So geht z. B. 1,4-Diphenyl-l-cyan-butadien-(1,3) (VI 2 Isomere) in c-2,l-4-Bis- 2-phenyl-2-cyan-vinyl]-r-l, t-3-diphenyl-cyclobutan fiber (VII 2 Isomere F 197° bzw. P 215°)5. 4-(E)-Nitro-I-phcnyl-... 

Behandlung von II mit Natrium-methanolat in Methanol/l,4-Dioxan (5 2 36 Rtdn. RiickflnB) fiihrt zu 2,4-Bis-[trans-2-phenyl-vinyl]-l,3-diphenyl-cyclobutan, welches durch praparative Dunnschicht-chromatographie gereinigt wird Ausbcute 70% F 85 87°. 

N,N -Diphenyl-cyclobutan-l,2,3,4-tetracarbonsaure-diimid2 8,7 g K-Phenyl-maleinsaure-imid und 1,8 g Benzophenon in 150 ml 1,4-Dioxan werden 24 Stdn. mit einem Quecksilber-Hochdruck-Brenner (Philips HPK 125 W) durch ein Glas-Filter unter Argon bei 15° belichtet. Man filtriert die ausgefallenen Kristalle ab (4,8 g 55%) und reinigt sie durch Sublimation bei 270°/0,l Torr. 

Diphenyl-athylen addiert Isobuten selektiv zum 2,2-Dimethyl-l,l-diphenyl-cyclobutan mit groBer Gruppenhaufung2, was auf der Grundlage eines biradikalischen Zwischenprodukts zu verstehen ist. Mit Cyclopenten entstehen 6,6-Diphenyl-bicydo [3.2.0]heptan und das En -Additionsprodukt 3-(l,l-Diphenyl-athyl)-cyclopent[Pg.370]

Ozonolyse von l,3-Dicarboxy-2,4-diphenyl-cyclobutan fiihrt analog zu 1,2,3,4-Tetracarb-oxy-cyclobutan (90%)l29. 

The catalyst was of Rh/diphos type, using as diphos ligands sulfonated (S,S)-1,2-bis(diphenylphosphanylmethyl)cyclobutane and sulfonated (2S,4S)-2,4-bis(diphenyl-... 

Bidentate chiral water-soluble ligands such as (S,S)-2,4-bis(diphenyl-sulfonatophosphino)butane BDPPTS (Fig. 2) or (R,R) 1,2-bis(diphenylsul-fonatophosphinomethyl)cyclobutane have been prepared [25]. Their palladium complexes catalyze the synthesis of chiral acids from various viny-larenes and an ee of 43% has been reached for p-methoxystyrene with the BDPPTS ligand. Furthermore, recycling of the aqueous phase has shown that the regio- and enantioselectivity are maintained and that no palladium leaches. 

The second example is an intermolecular crystal-state reaction. Cross-conjugated 1,5-disubstituted 1,4-dien-3-ones in solution undergo both cis-trans photoisomerization and photodimerization, yielding complex mixtures of products, including die all-trans-substituted cyclobutane 2 in the case of 1,5-diphenyl-1,4-pentadien-3-one. In contrast, dienones such as 3a in whose crystals adjacent molecules lie parallel and strongly overlapped react in the solid to give 3b as the sole photoproduct. This isomerically pure tricyclic diketone results, formally, from an eight-center dimerization. It is not formed in the reaction in solution, and could be prepared by other methods only with considerable difficulty (4). 

The cycloaddition of a variety of sulfur heterocycles to alkenes has also been reported. Dibromomaleic anhydride undergoes [ 2 + 2] cycloaddition to thiophen295 and to benzo[b]thiophen.296 The photoaddition of benzo-[(>]thiophen 1,1-dioxides to alkenes also affords cyclobutane derivatives.297 Of particular interest is the addition of 3-acetoxybenzo[6]thiophen (350) to cyclohexene to give the adduct (351), which on treatment with base, undergoes a retro-aldol ring opening to benzo[6]thiepinone (352).298 A mixture of stereoisomeric cyclobutane derivatives were obtained on irradiation of 2,6-diphenyl-4//-thiopyran-4-one 1,1-dioxide in cyclohexene.299 The [ 2 + 2] cycloaddition of sulfolen to maleic anhydride and to maleimide has been reported.300... 

The 2,4-disubstituted derivatives of the aforementioned 3-metallacyclobutanones allow for cis and trans isomers, much as for cyclobutanone and cyclobutane. It is found that the diphenyl species [Pt CHPhC(0)CHPh (PPh3)2] is synthesized with predominantly cis stereochemistry. This is consistent with stereochemical expectations—however, disconcertingly, there are no examples of disubstituted cyclobutanes (or derivatives) for which the enthalpy of formation of both the cis and trans isomers are both known to confirm this expectation. Gibbs free energy differences have been determined for the dimethyl , dichloro, dibromo and diiodo ° species, again in the expected order °. Indeed, the only case where the trans isomer is known to be more stable than the cis is the enigmatic bis-phenylsulfonyl species for which no explanation has been offered ... 

The Wolff rearrangement of six- and five-membered a-diazocycloalkanones has been extensively applied to the synthesis of highly strained frameworks. The rearrangement of an (x-diazo-cyclobutanone was reported from 2-diazo-3,4-bis(diphenylmethylene)cyclobutanone (1). The diazo ketone (1) was prepared by treatment of the 3,4-bis(diphenylmethyl-ene)cyclobutane-l,2-dione tosylhydrazone with alumina in 95% overall yield from the corresponding cyclobutanedione. Irradiation in the presence of water, alcohols and aniline afforded 1-carboxy-, 1-alkoxycarbonyl- and 1-phenylcarbamoyl-substituted 2,3-bis(diphenyl-methylene)cyclopropanes 2, respectively, in 13-87% yields. Thermal decomposition in aqueous dioxane afforded the cyclopropanecarboxylic acid 2 (X = OH) in 52% yield. ... 

Besides spin densities, the D parameter also depends on the interspin distance dAB [Eq. (8)]. Thus, structural effects on the D parameter may be probed through variations of the interspin distance dAB at constant spin densities pA and pB. The influence of such structural features on the D parameter is most prominently displayed by the two localized diradicals 5d [13] and 6b [15] (Table 5) for which the 1,3-diphenyl substitution provides essentially constant spin densities at the radical sites. Thus, any changes in the D parameter of these triplet diradicals should derive from geometrical effects on the interspin distance dAB. Optimized geometries from MO calculations for the cyclobutane-1,3-diyl (5d) gave an interspin distance of 208.5 pm and for the cyclopentane-1,3-diyl (6b) a value of 237.1 pm [64], which accounts nicely for the observed trends in the experimental D values that is, a lower D value (Table 5) for the latter due to the inverse d3 dependence [Eq. (8)]. 

Brij BSA Bu CBDTS CD CHIRAPHOS Cn COD Cp Cp CTAB DBA = seep.78 = bovine serum albumin = butyl = tetrasulfonated cyclobutane-DIOP, 37, see p. 17 = cyclodextrin = 2,3-bis(diphenylphosphino)butane = 1,4,7-trimethyl-1,4,7-triazacyclononane = 1,5-cyclooctadiene = r 5-cyclopentadienyl = ti5-CsMe5, r 5-pentamethylcyclopentadienyl = hexadecyltrimethylammonium bromide = 1,5-diphenyl-l, 4,-pentadiene-3-one (dibenzylideneacetone)... 

An cis-lrans-Isomerisierungen von Cyclobutan-Derivaten seien als Beispiele 1,2-Diphenyl-cyclobutan3 und 2-Phenyl-l-benzoyl-cyclobutan1 und 3-Oxo-l,2-dimethyl- bzw. 2-Oxo-l,3-diinethyl-cyclobutan5 genannt ... 

Bei trans-2-Nitro-1 -phenyl-athylen lieferfc die Krisfcall-Beliehtung topochcmisch kontrollicrt das c-2,t-4-Dinitro-r-l,t-3-diphenyl-cydobutcm (X 54% d.Th. F 183-1840)3. Damit verwandt ist die Reaktion von [Pg.314]

II t-3,t-4-DipJienyl-r-l,c-2-bis-[2-(2-phenyl-vinyl)-phenyr -cyclobutan III c-3,t-4-Diphenyl-r-l,t-2-bis-. . . ... 

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