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Pure Appl. Chem., 2010, Vol. 82, No. 7, pp. 1353-1364

Published online 2010-05-21

Phosphoramidite-rhodium complexes as catalysts for the asymmetric [2 + 2 + 2] cycloaddition of alkenyl isocyanates and alkynes

Rebecca Keller Friedman, Kevin M. Oberg, Derek M. Dalton and Tomislav Rovis*

Colorado State University, Fort Collins, CO 805235, USA

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.