Dedicated to Professor Paul Knochel on the occasion of his 70th birthday.
The catalytic enantioselective rearrangement of nitro-vinylcyclopropylacetaldehydes
has been studied using chiral secondary amines as catalysts. The reaction proceeds
through the in situ generation of a donor–acceptor cyclopropane, which rearranges to the corresponding
cyclopentene through an open conjugated iminium/unsaturated nitronate intermediate,
where the stereochemistry of the starting cyclopropane is lost. This intermediate
undergoes an intramolecular Michael reaction in which the asymmetric induction provided
by the catalyst allows the preparation of substituted nitrocyclopentenes in good yields
and with high stereocontrol. The obtained 2-nitrocyclopentenylacetaldehydes have been
transformed into valuable chiral cyclopentenones through Nef reaction with complete
retention of the stereochemical information.
Keywords
Enantioselective - Organocatalysis - Rearrangement - Vinylcyclopropane - Cyclopentene
- Donor–acceptor cyclopropane - Aldehyde - Nitroolefine
