Titanium(IV)-Catalyzed Stereoselective Synthesis of Spirooxindole-1-pyrrolines
journal contributionposted on 17.12.2015, 06:31 by Joseph J. Badillo, Carlos J. A. Ribeiro, Marilyn M. Olmstead, Annaliese K. Franz
A stereoselective cyclization between alkylidene oxindoles and 5-methoxyoxazoles has been developed using catalytic titanium(IV) chloride (as low as 5 mol %) to afford spiro[3,3′-oxindole-1-pyrrolines] in excellent yield (up to 99%) and diastereoselectivity (up to 99:1). Using a chiral scandium(III)–indapybox/BArF complex affords enantioenriched spirooxindole-1-pyrrolines where a ligand-induced reversal of diastereoselectivity is observed. This methodology is further demonstrated for the synthesis of pyrrolines from malonate alkylidene and coumarin derivatives.