Bl. Flynn et A. De Meijere, Unprecedented regio- and stereoselective conversion of 1-cyclopropyl-3-ethoxycyclopentadienes to 3-(E)-alkylidenecyclopentenes, J ORG CHEM, 64(2), 1999, pp. 400-404
Cyclopropylalkynes 1 were converted into cyclopropyl-substituted 3-ethoxy-5
-dimethylaminocyclopentadienes 4 via initially formed (beta-dimethylaminoet
henyl)carbene complexes 3 and their subsequent-formal [3 + 2] cycloaddition
to a second alkyne of type 1 (overall yields 51-59%). New regio- and stere
oselective 1,7-addition and 1,6-substitution reactions have been developed
that convert cyclopentadienes 4 into highly functionalized cyclopentenes 5
and 11, respectively (yields 98-99% and 61%, respectively). An in situ domi
no reaction consisting of a [3 + 2] cycloaddition and subsequent 1,7-additi
on has also been achieved (86% overall yield).