title: Phosphoramidite-Rhodium Complexes as Catalysts for the Asymmetric [2+2+2] Cycloaddition of Alkenyl Isocyanates and Alkynes.
abstract: The discovery and development of the asymmetric rhodium-catalyzed [2+2+2] cycloaddition of alkenyl isocyanates and exogenous alkynes to form indolizinone and quinolizinone scaffolds is described. This methodology has been expanded to include substituted alkenes and dienes, a variety of sterically and electronically diverse alkynes, and carbodiimides in place of the isocyanate. Through X-ray analysis of Rh(cod)/phosphoramidite complexes, additives that modify the enantio-determining step, and other experimental data, a mechanism has been proposed that explains lactam, vinylogous amide, and pyridone products and the factors governing their formation. Finally, we have applied this methodology to the synthesis of (+)-lasubine-II and (-)-209D.
authors.affiliation: Colorado State University, Fort Collins CO, 80523.
authors.forename: Rebecca Keller
authors.initials: RK
authors.lastname: Friedman
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Oberg
authors.forename: Derek M
authors.initials: DM
authors.lastname: Dalton
authors.forename: Tomislav
authors.initials: T
authors.lastname: Rovis