Et2AlCl-promoted asymmetric phenylseleno group transfer radical cyclization reactions of unsaturated beta-hydroxy esters.
We have developed a new method for asymmetric phenylseleno group transfer radical cyclization of unsaturated beta-hydroxy esters. Various unsaturated alpha-phenylseleno beta-hydroxy esters underwent radical cyclization in the presence of Et(2)AlCl in benzene with sunlamp irradiation at 25-30 degrees C to give mono- and bicyclic group-transferred products in an efficient and highly regioselective and diastereoselective manner. To rationalize the high diastereoselectivities observed in this reaction, we propose a model based on chelation control of the aluminum alkoxides that are formed in situ. We devised a general method to prepare chiral radical precursors from which we obtained highly optically pure mono- and bicyclic group transfer products. The synthetic advantages of this method are demonstrated by our formal total synthesis of (-)-wilforonide. This paper presents the first examples of stereoselective group transfer radical cyclizations that occur via 1,2-asymmetric induction.
Yang
Dan
D
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China. yangdan@hku.hk
Gao
Qiang
Q
Zheng
Bao-Fu
BF
Zhu
Nian-Yong
NY
D017607:Aluminum Compounds / Q000737:chemistry*; D003500:Cyclization; D004952:Esters / Q000138:chemical synthesis*; D005609:Free Radicals / Q000737:chemistry; D006880:Hydroxy Acids / Q000138:chemical synthesis; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D012643:Selenium / Q000737:chemistry
D017607:Aluminum Compounds; D004952:Esters; D005609:Free Radicals; D006880:Hydroxy Acids; D009942:Organometallic Compounds; D012643:Selenium