92013-62-2Relevant articles and documents
The effect of central bond torsional mobility on the Rydberg state ring opening of alkylcyclobutenes
Cook, Bruce H.O.,Leigh, William J.
, p. 680 - 688 (2007/10/03)
The stereochemistry of the π,R(3s) excited state ring opening of series of bicyclic alkylcyclobutenes has been studied in hydrocarbon solution with 228 nm excitation. In these compounds, the C=C bond is shared between the cyclobutene ring and a five-, six-, or seven-membered ancillary ring, which has the effect of restricting the torsional mobility about the central C - C bond in the isomeric diene products. It has previously been shown that monocyclic alkylcyclobutenes undergo stereospecific conrotatory ring opening upon excitation at the long wavelength edge of the π,R(3s) absorption band (228 nm), and nonstereospecific ring opening upon irradiation at shorter wavelengths (within the π,π* absorption band). Different behaviour is observed for the bicyclic systems studied in the present work. The bicyclo[3.2.0]hept-1-ene, bicyclo[4.2.0]oct-1-ene, and one of the bicyclo[5.2.0]non-1-ene derivatives yield nearly the same mixtures of E,E- and E,Z-diene isomers upon irradiation at 214 andre 228 nm, with the product mixtures being heavily weighted in favor of the isomer(s) corresponding to disrotatory ring opening. The results may indicate that the stereochemical characteristics of the Rydberg-derived ring opening of alkylcyclobutenes depends on the ability of the molecule to twist about the "central" bond (i.e., the C=C bond in the cyclobutene) as ring opening proceeds. It is proposed that restricting the torsional mobility about the central bond activates internal conversion from the π,R(3s) to the π,π* potential energy surface, from which predominant disrotatory ring opening ensues.
Cyclobutene photochemistry. Partial orbital symmetry control in the photochemical ring opening of a constrained cyclobutene
Leigh, William J.,Zheng, Kangcheng
, p. 4019 - 4020 (2007/10/02)
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Cyclization of Diacetylenes to E,E Exocyclic Dienes. Complementary Procedures Based on Titanium and Zirconium Reagents
Nugent, William A.,Thorn, David L.,Harlow, R. L.
, p. 2788 - 2796 (2007/10/02)
The intramolecular cyclization of diacetylenes has been achieved by using either of the reagent combinations Cp2TiCl2/PMePh2/Na(Hg) or Cp2ZrCl2/Mg/HgCl2 in solvent tetrahydrofuran.The procedures are compatible with a variety of saturated functionality (O,
