Fast and reversible migrations of N,S-centered groups around the perimeter of cyclopropene and cycloheptatriene rings

The kinetics and mechanism of circumambulatory rearrangements of N-centered (NCS) and S-centered (SPh, SC₃Ph₃, SC(OEt)=S) groups in corresponding derivatives of 1,2,3-triphenylcyclopropene and cycloheptatriene were studied by dynamic¹H and¹³C NMR spectroscopy. Migrations of the isothiocyanate group occur by the dissociation-recombination mechanism with intermediate formation of a tight ionic pair. Migrations of the phenylthio group around the perimeter of cyclopropene and cycloheptatriene rings occur by the 1,2-shift mechanism. It was found that rearrangements of theO-ethyl dithiocarbonate group inS-(1,2,3-triphenylcyclopropen-3-yl)-O-ethyl dithiocarbonate occur by the 3,3-sigmatropic shift mechanism. The molecular and crystal structure ofO-ethylS-(1,2,3-triphenylcyclopropen-3-yl) dithiocarbonate was studied by X-ray analysis.     

Electrochemical transformations of cycloheptatriene derivatives

Redox reactions of a series of substituted cycloheptatrienes are studied on a platinum electrode in acetonitrile using the cyclic voltammetry method. It was found that heptaphenyl-substituted cycloheptatrienes are irreversibly oxidized in two stages in the range of high anodic potentials to form unstable radical cations and dications. As opposed to the unsubstituted and monosubstituted cycloheptatrienes, they are not reduced at the potentials higher than ?2 V (SCE). A new stable radical anion was found in the reduction of N-cycloheptatrienylphthalimide. Its spin density distribution is studied by ESR spectroscopy.     

Chemistry of o-Benzoquinones and Masked o-Benzoquinones. VI. Cycloaddition of 6, 9 Dipropyl-1, 4-Dioxaspiro[4.5] Deca-6, 8-Dien-2, 10-Dione with Cycloheptatriene

Cycloaddition of masked o-benzoquinone, 6,9-dipropyl-1, 4-dioxaspiro[4.5]deca-6, 8-dien-2,10-dione, with cycloheptatriene afforded mainly [4π+2π] adducts which was transformed into 1, 4-dipropyl-5H-benzocycloheptene by hydrolysis, photolysis and dehydrogenation consecutively. These reaction sequences represent a novel method for the synthesis of 5H-benzocycloheptene from catechol via masked o-benzoquinone.     

A novel and unusual reaction of 1,2,3,4,5,6,7-hepta(methoxycarbonyl)-cyclohepta-2,4,6-trien-1-yl potassium with organic azides

A new type of rearrangement of an unsaturated seven-membered cycle into substituted ethenylcyclopentadienyl derivatives is described. This process proceeds via a cascade reaction of 1,2,3,4,5,6,7-hepta(methoxycarbonyl)cycloheptatrienyl potassium with organic azides (sulfonyl and carbonyl azides), and affords in one experimental step, N-substituted Z-1-[1,2-bis(methoxycarbonyl)-2-(methoxycarbonylamino)ethen-1-yl]-2,3,4,5-tetrakis(methoxycarbonyl)cyclopentadienyl anions, which represent a new type of chelating ligands.     

Vibrational cooling in the liquid phase studied by ultrafast investigations of cycloheptatriene

Solvent-mediated vibrational relaxation in UV pump–probe experiments has been studied using cycloheptatriene (CHT) and its perdeuterated counterpart (CHTd8) as model systems. Transient spectra containing absolute ε(t) values are obtained by a modified Sulzer–Wieland ansatz and a global fit function for vibrational relaxation is proposed.