Syntheses and Crystal Structures of the Cinchona Alkaloid Derivatives Used as Ligands in the Osmium-Catalyzed Asymmetric Dihydroxylation of Olefins

Experimental procedures for the preparation of two classes of derivatives of the cinchona alkaloids dihydroquinine and dihydroquinidine are described. Ligands (DHQ)2-PHAL, 1a, and (DHQD)₂-PHAL, 2a, are conveniently synthesized in good yield by the reaction of the corresponding alkaloid with 1,4-dichlorophthalazine in the presence of K₂CO₃ and KOH in refluxing toluene. Derivatives DHQ-PHN, 1b, and DHQD-PHN, 2b, are prepared through an Ullmann-type coupling between the 9-O-alkaloid sodium alkoxide and 9-iodophenanthrene in the presence of CuI and pyridine. Crystal structures for derivatives 2a and 2b are also presented. These four alkaloid derivatives serve as highly enantioselective ligands for the osmium tetraoxide catalyzed asymmetric dihydroxylation (AD) of olefins.