92013-62-2Relevant academic research and scientific papers
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, Adiabatic photochemical ring opening of alkylcyclobutenes
Leigh, William J.,Postigo, J. Alberto,Zheng
, p. 951 - 964 (2007/10/03)
The photochemistry of the cis and trans isomers of a series of dimethylbicyclo[n.2.0]alk-(n+2)-enes (n = 2-5) (bicyclic cyclobutene derivatives in which the C=C bond is shared by the two rings) in pentane solution is described. Irradiation of these compou
Novel Bicyclization of Enynes and Diynes Promoted by Zirconocene Derivatives and Conversion of Zirconabicycles into Bicyclic Enones via Carbonylation
Negishi, Ei-ichi,Holmes, Steven J.,Tour, James M.,Miller, Joseph A.,Cederbaum, Fredrik E.,et al.
, p. 3336 - 3346 (2007/10/02)
Enynes and diynes react with "ZrCp2" (where Cp = η5-C5H5) generated by treating Cl2ZrCp2 with Mg and HgCl2 or 2 equiv of an alkyllithium, such as n-BuLi, or a Grignard reagent, such as EtMgBr, and can produce in excellent yields zirconabicycles represented by 2 (M = Zr) and 8, respectively.Their protonolysis can provide the corresponding exocyclic alkenes and conjugated dienes 9, respectively.Iodinolysis of 2 (M = Zr) can give the corresponding diiodides in high yields, while carbonylation of 2 (M = Zr) can produce bicyclic enones 3 (Y = O) in moderate to goodyields.Although the bicyclization reaction fails with terminal alkyne containing substrates, various types of substituents on the alkyne moiety, such as alkyl, alkenyl, aryl, trialkylsilyl, and trialkylstannyl groups, can be accommodated.Investigation of the n-BuLi-Cl2ZrCp2 reaction has revealed that is gives first (n-Bu)2ZrCp2 at -78 deg C, which then decomposes to give Cp2Zr(CH2=CHEt), identified as its PMe3 complex 11.The PMe3-stabilized complex reacts with diphenylacetylene to produce a crystalline compound which has been identified as a zirconacyclopropene, 36a.This demonstrated, for the first time, the feasibility of converting alkynes into zirconacyclopropenes.The reaction of preformed, three-membered zirconacycles with alkynes gives five-membered zirconacycles.The reaction of diphenylacetylene is ca. 150 times as fast as that of (E)-stilbene.These results support a mechanism involving formation of a zirconacyclopropene intermediate followed by its intramolecular carbometalation with the alkene moiety of enynes for the Zr-promoted bicyclization of enynes.
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,
REACTION OF ZIRCONOCENE DICHLORIDE WITH ALKYLLITHIUMS OR ALKYL GRIGNARD REAGENTS AS A CONVENIENT METHOD FOR GENERATING A "ZIRCONOCENE" EQUIVALANT AND ITS USE IN ZIRCONIUM-PROMOTED CYCLIZATION OF ALKENES, ALKYNES, DIENES, ENYNES, AND DIYNES
Negishi, Ei-ichi,Cederbaum, Fredrik E.,Takahashi, Tamotsu
, p. 2829 - 2832 (2007/10/02)
Treatment of Cl2ZrCp2 with 2 equiv of alkylmetals (RM) containing Li or Mg, e.g., n-BuLi, in THF produces organozirconium species that act as sources of "ZrCp2," the latter product being a convenient reagent for preparing zirconacycles.
