131407-53-9Relevant articles and documents
Formation of Vinylcyclopropane and Cyclopentene Derivatives from Alkenyl-Substituted Chromium Carbene Complexes: Competition between Formal and Cycloadditions
Wienand, Anette,Reissig, Hans-Ulrich
, p. 957 - 965 (2007/10/02)
The alkenyl-substituted chromium carbene complexes 1 - 4 were synthesized following the method of Aumann which starts from the corresponding aldehydes.At 80 deg C the styryl-substituted complex 1 and electron-deficient olefins smoothly provide vinylcyclopropane derivatives 6, 8, 10, and 12 in good yields.On the other hand, methyl acrylate and the anisyl- and furyl-substituted vinylcarbene complexes 2 and 3 give mixtures of the expected vinylcyclopropanes and of cyclopentene derivatives.The pyrrolyl-substituted complex 4 and methyl acrylate exclusively afford the cyclopentenes 24a/b which are the result of a hitherto unprecedented formal cycloaddition of the vinylcarbene complex to the olefin.However, there are strong arguments suggesting the corresponding vinylcyclopropanes as intermediates.The very smooth vinylcyclopropane -> cyclopentene rearrangement probably occurs via zwitterionic intermediates that are well-stabilized by donor and acceptor substituents.Hydrolysis of 24a/b to the cyclopentanone derivatives 25a/b demonstrates that this new route to five-membered carbocycles should have synthetic potential.
