title: PuPHOS: a synthetically useful chiral bidentate ligand for the intermolecular Pauson-Khand reaction.
abstract: Here we describe the synthesis and use of the Pulegone-derived bidentate P,S ligands PuPHOS and CyPuPHOS in the intermolecular Pauson-Khand reaction. Ligand exchange reaction of hexacarbonyldicobalt-alkyne complexes with PuPHOS provides a diasteromeric mixture of complexes (up to 4.5:1) from which the major isomers can be conveniently separated by simple crystallization. An isomerization-crystallization sequence of the original mixture results in a dynamic resolution that allows the preparation of the pure major Co(2)(mu-TMSC(2)H)(CO)(4)-PuPHOS (15a) in a multigram scale. Pauson-Khand reaction of 15a with norbornadiene provided, for the first time, the corresponding enone 18 with up to 93% yield and 97% ee. The use of (+)-18 as a surrogate of chiral cyclopentadienone is also demonstrated. Copper-catalyzed Michael addition of a Grignard reagent followed by removal of the TMS group with TBAF were the most reliable methods to transform (+)-18 into valuable starting materials 20a-e for the enantioselective synthesis of cyclopentenoid systems.
authors.affiliation: Unitat de Recerca en Síntesi Asimètrica (URSA), Parc Científic de Barcelona and Departament de Química Orgànica, Universitat de Barcelona, c/Josep Samitier, 1-5. 08028-Barcelona, Spain. xverdaguer@pcb.ub.es
authors.forename: Xavier
authors.initials: X
authors.lastname: Verdaguer
authors.forename: Agustí
authors.initials: A
authors.lastname: Lledó
authors.forename: Cristina
authors.initials: C
authors.lastname: López-Mosquera
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Maestro
authors.forename: Miquel A
authors.initials: MA
authors.lastname: Pericàs
authors.forename: Antoni
authors.initials: A
authors.lastname: Riera