title: Enantioselective palladium-catalyzed addition of 1,3-dicarbonyl compounds to an allene derivative.
abstract: Enhancing atom economy of the metal-catalyzed asymmetric allylic alkylation (AAA) shifts from the usual nucleophilic displacement of a leaving group to an addition of a pronucleophile to a double bond. Using 1-alkoxyallenes as proelectrophiles, the palladium-catalyzed AAA proceeds with 1,3-dicarbonyl compounds as pronucleophiles with excellent regioselectivity and enantiomeric excess under optimized conditions. The pH of the medium proved crucial for reactivity/selectivity. By using the more acidic Meldrum's acids, the reactions required a co-catalytic amount of Brønsted acid, such as trifluoroacetic acid. Single regioisomeric products of 82-99 % ee were obtained. On the other hand, the less acidic 1,3-diketones failed to react under such conditions. The fact that a less acidic acid like benzoic acid sufficed, suggested the need for general base catalysis as well. Thus, a mixture of triethylamine and benzoic acid proved optimal (ee's 93-99). Employment of the (R,R)-phenyl Trost ligand gave a product with S configuration. A model to rationalize the results has been developed.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA. bmtrost@stanford.edu
authors.forename: Barry M
authors.initials: BM
authors.lastname: Trost
authors.forename: Alessandro B C
authors.initials: AB
authors.lastname: Simas
authors.forename: Bernd
authors.initials: B
authors.lastname: Plietker
authors.forename: Christoph
authors.initials: C
authors.lastname: Jäkel
authors.forename: Jia
authors.initials: J
authors.lastname: Xie
mesh_terms: D000466:Alkadienes / Q000737:chemistry*; D002384:Catalysis; D010165:Palladium / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism
chemical_list: D000466:Alkadienes; C025947:propadiene; D010165:Palladium