Enantioselective Rhodium(I) Donor Carbenoid-Mediated Cascade Triggered by a Base-Free Decomposition of Arylsulfonyl Hydrazones

• Published in: Chemistry : a European journal 2015-11, Vol.21 (45), p.16240-16245
• Main Authors: Torres, Òscar, Parella, Teodor, Solà, Miquel, Roglans, Anna, Pla-Quintana, Anna
• Format: Article
• Language: English
• Subjects: carbenoids; cascade; Cascades; Catalysis; Chemistry; cyclization; Decomposition reactions; density functional calculations; Deuterium; Enantiomers; Formations; Hydrazones; Hydrides; Hydrogen bonds; Insertion; Mathematical analysis; Rhodium; Stereoselectivity; Substrates
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201502909

The reaction of diyne arylsulfonyl hydrazone substrates under rhodium(I)/BINAP catalysis gives access to sulfonated azacyclic frameworks in a highly enantioselective manner. This new cascade process considerably increases the molecular complexity by generating two CC bonds, one CS bond, and one CH bond. Theoretical calculations, competitive experiments, and deuterium labeling have jointly been used to propose a mechanism that accounts for the reaction. The mechanism involves the formation of vinyl rhodium carbenoids, hydride migratory insertion, and intermolecular stereoselective nucleophilic attack. The last two steps are the key to the stereoselectivity of the process. La reacció catalitzada per rodi(I)/BINAP de substrats contenint dos alquins i una sulfonilhidrazona permet sintetitzar compostos nitrogenats amb un grup sulfona de forma altament enantioselectiva. Aquest nou procés en cascada augmenta considerablement la complexitat molecular ja que genera dos enllaços CC, un enllaç CS i un enllaç CH. S′ha proposat un mecanisme per al procés desenvolupat en base als resultats obtinguts mitjançant càlculs DFT, experiments de competició i marcatge amb deuteri. El mecanisme involucra la formació d′un vinilcarbenoid de rodi, una inserció migratòria d′hidrur i un atac nucleofílic intermolecular estereoselectiu. Els dos darrers passos són claus per a l′enantioselectivitat del procés. Rhoad to the cascade! The decomposition of the arylsulfonyl hydrazone in the presence of a rhodium source generates a donor RhI carbenoid which initiates an intermolecular cascade process. Chiral sulfones are efficiently synthesized in a one‐step reaction from linear achiral substrates (see scheme; COD=Cyclooctadiene).