Huang DJ, Rayabarapu DK, Li LP, Sambaiah T, Cheng CH
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan.
Chemistry. 2000 Oct 16;6(20):3706-13. doi: 10.1002/1521-3765(20001016)6:20<3706::aid-chem3706>3.0.co;2-p.
Oxabenzonorbornadienes 1 and 2 and azabenzonorbornadiene 3 undergo [2+2] cycloaddition with alkynes (PhC triple bond Ph, PhC triple bond CMe, PhC triple bond CCO2Et, PhC triple bond CCH(OEt)2, and HC triple bond C(CH2)4Me) in the presence of [Ni(PPh3)2Cl2], PPh3, and Zn powder in toluene to afford the corresponding exo-cyclobutene derivatives 4a-e, 5a-e, and 6 in fair to excellent yields. Under similar conditions. EtCO2C triple bond CCO2Et does not react with 1 in toluene to give the [2+2] cycloaddition product, but in acetonitrile, the catalytic [2+2] cycloaddition proceeds and cycloadduct 4 f is isolated in 83% yield. At high temperature, these cyclobutene derivatives readily undergo ring expansion to yield the corresponding 8-membered carbocyclic dienes. Thus, flash vacuum pyrolysis of 4a, 4d, 4f, 6, and 14 at 500 degrees C affords dienes 13a-d and 15 in 70-96% yields. This interesting ring expansion may be viewed as the insertion of an alkyne moiety into the carbon-carbon double bond of a cyclic olefin resulting in the enlargement of the ring by two carbons. Compound 13a is readily deoxygenated by TiCl4 and Zn in THF to give a cyclooctatetraene derivative 16 in 89% yield.
氧化苯并降冰片二烯1和2以及氮杂苯并降冰片二烯3在甲苯中，于[Ni(PPh₃)₂Cl₂]、三苯基膦和锌粉存在下，与炔烃（PhC≡Ph、PhC≡CMe、PhC≡CCO₂Et、PhC≡CCH(OEt)₂和HC≡C(CH₂)₄Me）发生[2+2]环加成反应，以中等至优异的产率得到相应的外型环丁烯衍生物4a - e、5a - e和6。在类似条件下，EtCO₂C≡CCO₂Et在甲苯中不与1反应生成[2+2]环加成产物，但在乙腈中，催化[2+2]环加成反应进行，环加成产物4f以83%的产率分离得到。在高温下，这些环丁烯衍生物容易发生扩环反应，生成相应的8元碳环二烯。因此，4a、4d、4f、6和14在500℃下进行快速真空热解，以70 - 96%的产率得到二烯13a - d和15。这种有趣的扩环反应可以看作是炔烃部分插入环状烯烃的碳 - 碳双键中，导致环扩大两个碳原子。化合物13a在四氢呋喃中容易被四氯化钛和锌脱氧，以89%的产率得到环辛四烯衍生物16。
