849024-97-1Relevant academic research and scientific papers
Directing the Activation of Donor–Acceptor Cyclopropanes Towards Stereoselective 1,3-Dipolar Cycloaddition Reactions by Br?nsted Base Catalysis
Blom, Jakob,Vidal-Albalat, Andreu,J?rgensen, Julie,Barl?se, Casper L.,Jessen, Kamilla S.,Iversen, Marc V.,J?rgensen, Karl Anker
, p. 11831 - 11835 (2017)
The first stereoselective organocatalyzed [3+2] cycloaddition reaction of donor-acceptor cyclopropanes is presented. It is demonstrated that by applying an optically active bifunctional Br?nsted base catalyst, racemic di-cyano cyclopropylketones can be activated to undergo a stereoselective 1,3-dipolar reaction with mono- and polysubstituted nitroolefins. The reaction affords functionalized cyclopentanes with three consecutive stereocenters in high yield and stereoselectivity. Based on the stereochemical outcome, a mechanism in which the organocatalyst activates both the donor-acceptor cyclopropane and nitroolefin is proposed. Finally, chemoselective transformations of the cycloaddition products are demonstrated.
Structural optimization of thiourea-based bifunctional organocatalysts for the highly enantioselective dynamic kinetic resolution of azlactones
Berkessel, Albrecht,Mukherjee, Santanu,Mueller, Thomas N.,Cleemann, Felix,Roland, Katrin,Brandenburg, Marc,Neudoerfl, Joerg-M.,Lex, Johann
, p. 4319 - 4330 (2008/09/18)
This article describes the synthesis of a library of structurally diverse bifunctional organocatalysts bearing both a quasi-Lewis acidic (thio)urea moiety and a Bronsted basic tertiary amine group. Sequential modification of the modular catalyst structure and subsequent screening of the compounds in the alcoholytic dynamic kinetic resolution (DKR) of azlactones revealed valuable structure-activity relationships. In particular, a "hit-structure" was identified which provides e.g. N-benzoyl-tert-leucine allyl ester in an excellent enantiomeric excess of 95%. The Royal Society of Chemistry 2006.
