72610-87-8

Upstream product

• 3469-06-5 benzocyclobutenone 
• 78329-07-4 Bicyclo[4.2.0]octa-1,3,5-trien-7-yl-triphenyl-phosphonium; bromide 
• 72610-89-0 Lithium Salt of Benzocyclobutenone Tosylhydrazone 
• 69139-15-7 Sodium Salt of Benzocyclobutenone Tosylhydrazone 

Downstream Products

• 87-41-2 2-benzofuran-1(3H)-one 
• 3469-06-5 benzocyclobutenone 
• 40261-88-9 dibenzocycloocten-11,12(5H,6H)-dione 
• 113446-65-4 spiro-1'(3'H)-one 

Relevant academic research and scientific papers

Synthesis, structural characterization and photoisomerization of cyclic stilbenes

Six cyclic stilbene derivatives with hindered free rotation around the C(vinyl)-C(phenyl) single bond were synthesized by McMurry coupling. The torsion angles around the double and the single bond, and the CC bond length were obtained for many of the compounds from their solid-state structures. The photochemical isomerization was subsequently investigated for all derivatives under various conditions. The parent 1-(1-tetralinylidene)tetralin underwent efficient oxidative electrocyclization. The 2,2,2′,2′- tetramethylated analogue was resistant towards photooxidation, however, its cis-isomer thermally reisomerized to the more stable trans-isomer.

Time-Resolved Photochemistry of Stiffened Stilbenes

Broadband transient absorption spectroscopy is used to study the photoisomerization of stiffened stilbenes in solution, specifically E/Z mixtures of bis(benzocyclobutylidene) (t4, c4) and (E)-1-(2,2-dimethyltetralinylidene)-2-2-dimethyltetraline (t6). Upon excitation to S1, all evolve to perpendicular molecular conformation P, followed by decay to S0, while the spectra and the kinetic behavior crucially depend on the size of the stiffening ring. In 4, contrary to all previously studied stilbenes, the trans and cis absorption and excited-state spectra are nearly indistinguishable, while the corresponding isomerization times are comparable: τi = 166 ps for t4 and τi = 64 ps for c4 in n-hexane, as opposed to 114 and 45 ps in acetonitrile, respectively. Faster isomerization in polar solvents agrees with the zwitterionic character of the P state. In t6, torsion to P is effectively barrier-less and completes within 0.3 ps, the S1 → P evolution being directly traceable through the transient spectra of stimulated emission and that of excited-state absorption. In n-hexane, the P state is remarkably long-lived, τP = 1840 ps, but the lifetime drops down to 35 ps in acetonitrile. The trans-to-cis photoisomerization yield for t6 is measured to be 20%, while for t4, it remains uncertain. We discuss the effects of stiffening and substitution on the formation and lifetime of the intermediate states through which the stilbene molecules evolve on the S1 energy surface.

Cyclic trans-stilbenes: Synthesis, structural and spectroscopic characterization, photophysical and photochemical properties

trans-Stilbene and several cyclic derivatives with hindered free rotation around the C(vinyl)-C(phenyl) single bond were studied by various spectroscopic techniques. Those derivatives which contain 6- or 7-membered aliphatic rings do not exhibit any measurable S1 → S0 fluorescence. The introduction of two methoxy groups into the 6-membered aliphatic ring derivative accelerates its photoreactivity to such an extent that fluorescence or resonance Raman spectroscopy investigations become impossible. The introduction of aliphatic rings has only a little effect on the frequency of the phenyl-ring stretching vibrations, but pronounced ones on the IR and Raman intensities. The frequency of the vinylic stretching mode is downshifted between 5 and 100 cm-1 except in the case of the derivative with the 4-membered ring, which experiences a hypsochromic shift of 80 cm-1. Only trans-stilbene and its 4-membered cyclic analogues were amenable to fluorescence lifetime measurements. Analysis of VT-NMR spectra of stilbene 7 reveals a barrier of 15.9 kcal mol-1 for equilibration of aliphatic equatorial and axial H-atoms.

Influence of solvent viscosity on the photoisomerization of a novel trans-stilbene derivative with hindered single bond torsion

Fluorescence life-time measurements were performed at elevated pressure and temperature to examine the viscosity dependence of the rate of photoinduced isomerization, kiso, in a stilbene derivative in which the single bond torsion is hindered by the introduction of CH2 bridges. The results obtained with n-hexane and methylcyclohexane as solvents (0.2 mPa siso=C·(η/mPa s)-a·exp(-EA/RT). The value for a drops from about 0.30 in n-hexane to about 0.15 in methylcyclohexane thus pointing to solvent specific contributions to the friction. The derived activation energies EA are about 12.8 and 12.5 kJ mol-1 in n-hexane and methylcyclohexane, respectively.

Radical-Stabilization-Energy - the MMEVBH Force Field

Making use of the VB method of Malrieu et al. a force field has been developed, which allows to calculate heats of formation of hydrocarbons (conjugated and non-conjugated olefins, radicals and diradicals) with high accuracy.With this method radical stabilization energies (RSE) for a great number of delocalized radicals are calculated and compared with experimental values, derived from shock-tube measurements of dissociation energies or from rotational barriers of substituted olefins.A detailed analysis of the RSE with respect to structure, substituents, strain, and aromaticity is presented. - Key Words: Resonance energy / Heats of formation / Single pulse shock tube / Intrisic rotational barrier

Photochemical Decomposition of Benzocyclobutenone p-Toluenesulfonylhydrazone

The photochemical decomposition of benzocyclobutenone p-toluenesulfonylhydrazone led to a wide variety of products including the E- and Z-isomers of 1,1'-bi(benzocyclobutenylidene) 6a; cis-trans-benzocyclobutenylidene trimer 7; cyclohepatrienes 8-10; benzocyclobutenone azine in it's anti-anti(11), anti-syn (12), and syn-syn conformations (13); anti- and syn-benzocyclobutenone N-benzocyclobutenyl-N-tosylhydrazone (14 and 15, respectively); (benzocyclobutenyl)hydrazine (16); benzocyclobutenyl p-tolyl sulfone (17); and benzocyclobutenone 1.Their isolation, identification and mechanism of formation are discussed.The data indicate that while the addition of arylcarbenes to alkenes results in the preferential formation of the more-hindered syn products, arylcarbene 5 adds to aryl olefins (styrenes and dimer 6) in a stereospecific anti orientation to give the less-hindered product.In addition, the minimal steric effects observed in these systems presumably results from the 90 deg angle of the cyclobutyl ring, which pulls the phenyl ring back and thus minimizes its steric contribution.

Synthesis and Rearrangements of 1,1'-Bi(benzocyclobutylidene) and its Derivatives

Convenient new preparations of 1-halogeno-1,2-dihydrobenzocyclobutenes (5) and (6) and 1,1'-bi(benzocyclobutylidene) (4) are described.The hydrocarbon (4) is susceptible to cationic rearrangements: it forms 5,10-dihydroindenoindene (16) on protonation in acetic anhydride, and is oxidised by selenium(IV) oxide to a mixture of the spiroketone (17) and 5H-indeno-benzopyran-2-one (18).The mechanisms of these and other rearrangements are discussed.

Benzocyclobutenylidene-Cycloadditions, Reactivity, and Multiplicity

EHT and CNDO/2 calculations on benzocyclobutenylidene (6) are described.Flash pyrolysis of the tosylhydrazone salt 7 affords benzocyclobutene and o-xylene in low yield, along with the formal syn and anti carbene dimers 13 and 14.Condensed-phase reactions were achieved by photolysis of the salt 15.Benzocyclobutenylidene (6) gave rise to the formal carbene dimers 17 and 18.Insertion of carbene 6 into the carbon-hydrogen bonds of 2,3-dimethylbutane produced the benzocyclobutenes 20 and 21 (insertion ratio tertiary:primary = 9:1).Cycloaddition of 6 to olefins gave only spirohexene derivatives 22.Multiplicity studies of 6 with cis or trans olefins indicated that 6 undergoes cycloaddition in a stereospecific manner.Competition experiments using dienes and monoolefins implicate an equilibrium between singlet and triplet 6.Further competition experiments with styrene/para-substituted styrene pairs demonstrated that 6 reacts faster with electron-poor styrenes.Possible explanations for this apparent anomaly are discussed.