Enantioselective Reactions of 2-Sulfonylalkyl Phenols with Allenic Esters: Dynamic Kinetic Resolution and [4+2] Cycloaddition Involving ortho-Quinone Methide Intermediates.

ABSTRACT

We report herein a dynamic kinetic resolution (DKR) involving ortho-quinone methide (o-QM) intermediates. In the presence of Et3 N and the cinchonine-derived nucleophilic catalyst D, the DKR of 2-sulfonylalkyl phenols with allenic esters afforded chiral benzylic sulfones in 57-79 % yield with good to excellent enantioselectivity (85-95 % ee). Furthermore, with 2-(tosylmethyl)sesamols or 2-(tosylmethyl)naphthols, from which stable o-QM substrates can be generated, a formal [4+2] cycloaddition delivered 4-aryl- or alkyl-substituted chromans with excellent enantioselectivity (88-97 % ee).