Enantioselective Organocatalytic C-C Ring Construction

Abstract

Ming Yan of Sun Yat-sen University, Guangzhou, optimized (Synlett 2010, 266) the organocatalyzed addition of 2 to a cyclic enone 1, establishing the cyclopropane 3 with high diastereo- and enantiocontrol. Benjamin List of the Max-Planck-Institut Mülheim devised (Angew. Chem. Int. Ed. 2010, 49, 4136) an organocatalyst for the enantioselective methanolysis of the anhydride 4. Other ring sizes worked as well. Hisashi Yamamoto of the University of Chicago reported (Organic Lett. 2010, 12, 2476) the organocatalyzed addition of the ketone silyl enol ether 6 to the aldehyde 7, to give the syn aldol product 8 in high ee. Gang Zhao of the University of Science and Technology, Hefei, established (Angew. Chem. Int. Ed. 2010, 49, 4467) an organocatalyst for the enantioselective addition of the allene ester 10 to 9. Marcus A. Tius of the University of Hawaii uncovered (J. Am. Chem. Soc. 2010, 132, 8266) conditions for the enantioselective Nazarov cyclization of 12 to 13. Karl A. Scheidt of Northwestern University devised (Organic Lett. 2010, 12, 2830) an easily scaled protocol for the cyclization of the prochiral diketone 14 to the β-lactone 15. Thermolysis then converted 15 to the corresponding cyclopentene. Yixin Lu of the National University of Singapore showed (Organic Lett. 2010, 12, 2278) that the simple combination of commercial cinchonidine with (+)-camphorsulfonic acid gave a catalyst that effected the room-temperature conjugate addition of 16 to 1. Hiyoshizo Kotsuki of Kochi University combined (Organic Lett. 2010, 12, 1616) 1,2-diaminocyclohexane with cyclohexane-1,2-bis carboxylate to give a similarly simple catalyst system, that effected Robinson annulation of 18 to 20. Binding an organocatalyst to a polymer simplifies recovery and reuse. Tore Hansen of the University of Oslo reported (J. Org. Chem. 2010, 75 , 1620) a bottom-up approach to such polymer-bound catalysts. The bound proline worked well for the condensation of 21 with 22. The corresponding polymeric diphenyl OTMS (Jørgensen-Hayashi) catalyst was sluggish, but it effected the three-component coupling of 24, 25, and 26 in high ee. Two cascade cyclizations warrant particular mention. The racemic cyclization of 28 is expected to be facile in the presence of HCl.