Bicyclic alkenes 1a-e and 5 undergo [2 + 2] cycloaddition with a variety of alkynes PhC(triple bond)CPh, (TMS)C(triple bond)CH, HC(triple bond)C(CH(3))(2)OH, (TMS)C(triple bond)CCO(2)Et, PhC(triple bond)CCH(3), C(2)H(5)C(triple bond)CC(2)H(5), CH(3)C(triple bond)CC(3)H(7), and CH(3)C(triple bond)CC(2)H(5) in the presence of Co(PPh(3))(2)I(2), PPh(3), and Zn powder in toluene to afford the corresponding
readily undergo ringexpansion to yield the corresponding 8-membered carbocyclic dienes. Thus, flashvacuumpyrolysis of 4a, 4d, 4f, 6, and 14 at 500 degrees C affords dienes 13a-d and 15 in 70-96% yields. This interesting ringexpansion 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
Ruthenium-Catalyzed Coupling of Oxabenzonorbornadienes with Alkynes Bearing a Propargylic Oxygen Atom: Access to Stereodefined Benzonorcaradienes
作者:Alphonse Tenaglia、Sylvain Marc、Laurent Giordano、Innocenzo De Riggi
DOI:10.1002/anie.201104589
日期:2011.9.19
Stereodefined: The title reaction provides an atom‐economic route to benzonorcaradienes. The diastereoselectivity of the coupling relies upon the structure of the alkene; unsubstituted bicyclic alkenes afforded exclusively exo‐benzonorcaradienes (see scheme) whereas the bicyclic alkenes with substituents at the bridgehead positions resulted in endo‐benzonorcaradienes.