An Enantioselective Synthesis of 2-Aryl Cycloalkanones by Sc-Catalyzed Carbon Insertion
摘要:
Current methods for asymmetric alpha-arylation require blocking groups to prevent reaction at the alpha'-carbon, basic conditions that promote racemization, or multistep synthesis. This work records the first catalytic enantioselective examples of the diazoalkane-carbonyl homologation reaction. Medium ring 2-aryl ketones are prepared in one step in up to 98:2 er and 99% yield from the unsubstituted lower homologue by Sc-catalyzed aryldiazomethyl insertion with simple bis- and tris(oxazoline) ligands.
BF3 can be used in combination with organolithium/strong Lewis base complexes for the enantioselective nucleophilic ring-opening or the carbenoidic rearrangement of various meso-oxiranes with excellent yields and ee values of up to 87 %. Mechanistic aspects of these reactions are considered.
Nonenzymatic kinetic resolution of racemicsecondaryalcohols is an efficient synthetic method to obtain optically active compounds in organic chemistry. Catalytic asymmetric acylation of racemicsecondaryalcohols has been successfully performed with achiral benzoyl chloride in the presence of only 0.3 mol% of chiral diamine (3) derived from (S)-proline, combined with 0.5 equivalent of triethylamine
Cyclooctene oxide 1, cycloocta-1,3-diene oxide 4, and cycloocta-1,5-diene oxide 7 react with organolithium reagents by nucleophilic opening or α- or β-deprotonation. The addition of BF3·Et2O affects the course of the reaction, and also strongly accelerates it. If (−)-sparteine is present, a moderate to high asymmetric induction is obtained.