Thermal rearrangements of 9,10-bis(trifluorovinyl)phenanthrene
摘要:
Results from a study of the thermal unimolecular rearrangement of 9,10-bis(trifluorovinyl)-phenanthrene are reported. Kinetic and product studies indicate that it is unexpectedly resistant to rearrangement, that its expected 6pi electrocyclic rearrangement plays but a minor role, and that the major rearrangement process was a virtually unprecedented thermal reaction for 1,3,5-trienes, that of conversion to a bicyclo[3.1.0]hex-2-ene system (7). Activation parameters are provided for the minor electrocyclic process (DELTAH(double dagger) = 29.9 kcal/mol; DELTAS(double dagger) = -19.6 eu) and for the conversion to 7 (DELTAH(double dagger) = 34.4 kcal/mol; DELTAS(double dagger) = -6.6 eu) as well as for the secondary conversions of 7 to 4-(difluoromethylidene)-3,3,5,5-tetrafluoro-1,2-(9,10-phenanthro)cyclopent-1-ene (8) (DELTAH(double dagger) = 31.3 kcal/mol; DELTAS(double dagger) = -12.7 eu) and to 1,2-(9,10-phenanthro)-3,5,5-trifluoro-4-(trifluoromethyl)-1,3-cyclopentadiene (9) (DLETAH(double dagger) = 31.4 kcal/mol; DELTAS(double dagger) = -13.4 eu). A rarely encountered fluorine steric effect deriving from the stringent steric demands of the reaction's boat-like transition state is invoked to explain the inhibition of 1's electrocyclic process, while equally rare thermal 1,2-fluorine atom shifts are proposed to explain the rearrangement of 7.
Sonogashira Coupling Using Bulky Palladium-Phenanthryl Imidazolium Carbene Catalysis
摘要:
[GRAPHICS]Bulky phenanthracenyl imidazolium-derived carbene ligands were investigated for copper-free Sonogashira coupling with terminal acetylenes. Aryl bromides and iodides gave coupled products in excellent yields from the Pd(PPh3)(2)Cl-2 complex with potassium t-butoxide and 18-crown-6 in THF. A remarkable dependence on the size of the ligand was found. The highest yields were obtained with the bulky 2,9-dicyclohexyl-10-phenanthryl ligand 5.
Phenanthrene-Fused Azo-ene-ynes: Synthesis of Dibenzo[<i>f</i>,<i>h</i>]cinnoline and Dibenzo[<i>e</i>,<i>g</i>]isoindazole Derivatives
作者:Brian S. Young、Felix Köhler、Rainer Herges、Michael M. Haley
DOI:10.1021/jo201378t
日期:2011.10.21
The cyclization reactions of a phenanthreno-fused azo-ene-yne compound have been studied both experimentally and computationally. Experimental results show that this system is prone to dimerization, more so than previously studied naphthalene- and benzene-based analogues. Calculations reveal that pyrazoles and arene-fused pyrazoles strongly stabilize carbenes in the 5-position through “coarctate conjugation”