The role of the achiral template in enantioselective transformations. Radical conjugate additions to alpha-methacrylates followed by hydrogen atom transfer.
We have evaluated various achiral templates (1a-g, 10, and 16) in conjunction with chiral Lewis acids in the conjugate addition of nucleophilic radicals to alpha-methacrylates followed by enantioselective H-atom transfer. Of these, a novel naphthosultam template (10) gave high enantioselectivity in the H-atom-transfer reactions with ee's up to 90%. A chiral Lewis acid derived from MgBr(2) and bisoxazoline (2) gave the highest selectivity in the enantioselective hydrogen-atom-transfer reactions. Non-C(2) symmetric oxazolines (20-25) have also been examined as ligands, and of these, compound 25 gave optimal results (87% yield and 80% ee). Insights into rotamer control in alpha-substituted acrylates and the critical role of the tetrahedral sulfone moiety in realizing high selectivity are discussed.
Sibi
Mukund P
MP
Department of Chemistry, North Dakota State University, Fargo, North Dakota 58105-5516, USA.
Sausker
Justin B
JB
D000143:Acids / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D007769:Lactams / Q000737:chemistry; D008689:Methacrylates / Q000737:chemistry*; D008958:Models, Molecular; D009282:Naphthalenesulfonates / Q000737:chemistry*; D023303:Oxazolidinones / Q000737:chemistry*; D011760:Pyrrolidinones / Q000737:chemistry*; D013237:Stereoisomerism; D013698:Templates, Genetic
D000143:Acids; D007769:Lactams; D008689:Methacrylates; C450999:N-(2-methylpropenoyl)-1,8-naphthosultam; D009282:Naphthalenesulfonates; D023303:Oxazolidinones; D011760:Pyrrolidinones; D006859:Hydrogen