The synthesis of 3-aryl-4-nitrocyclohexanones has been achieved from the Morita–Baylis–Hillmanadducts of β-arylnitroethylenes. The strategy involves proline-catalyzed diastereoselective intramolecularMichaeladdition to obtain 3,4-trans-disubstituted cyclohexanones. This method provides a facile access to (±)-epibatidine analogues.
Selective Access to Both Diastereoisomers in an Enantioselective Intramolecular Michael Reaction by Using a Single Chiral Organocatalyst and Application in the Formal Total Synthesis of (−)-Epibatidine
作者:Kim L. Jensen、Christian F. Weise、Gustav Dickmeiss、Fabio Morana、Rebecca L. Davis、Karl Anker Jørgensen
DOI:10.1002/chem.201202353
日期:2012.9.17
Two in one: Both diastereoisomers of 4‐nitro‐3‐substituted cyclohexanones are accessed selectively by an intramolecular Michael reaction using a single chiral aminocatalyst (see scheme). Mechanistic studies show that the reaction is selective for the cis‐diastereoisomer and that the trans‐diastereoisomer arises over time. DFT calculations suggest that the cis‐selectivity is due to a favorable electrostatic
Two different syntheses of Epibatidine (1) were designed and carried out using easily accessible reagents and convenient reaction conditions. The ring closure of the prochiral precursor 4 catalyzed by optically active α-phenyl-ethyl-amine gave the key intermediate 5 in over 80% ee from which the natural product (−)-1 has been prepared.