A New Approach to Asymmetric Synthesis of Polycycles on the Basis of o-Quinodimethane Generation

Article abstract of DOI:10.1021/ja00344a028

The fluoride anion induced 1,4-elimination of 2-phenyl>-3,3-dimethyloxazolidinium salts generates (E,E)-α-alkyl-α'-<2-(dimethylamino)alkyl>-o-quinodimethane intermediates, which are trapped stereoselectively with dienophiles to give polycycles.Intramolecular cyclization of 2-phenyl>-3,3-dimethyl-4-(R)-methyl-5(R)-phenyloxazolidinium triflate at 0 deg C produces a 3:1 diastereoisomeric mixture of 6-<2(R)-(dimethylamino)-1(R)-phenylpropoxyl>-trans-octahydrophenanthrene, which is converted by hydrogenolysis on Pd/C to trans-octahydrophenanthrene with <α>_D +46.6 deg (50percent ee).Similarly, intramolecular cyclization of 2-phenyl>-3,3-dimethyl-4(S)-methoxymethyl-5(S)-phenyloxazolidinium triflate produces, after hydrogenolysis on Pd/C, trans-octahydrophenanthrene with <α>_D -51.1 deg (55percent ee).The enantioselection in the cycloaddition with o-quinodimethane intermediate may be accounted for on the basis of ?-stacking interaction in the Diels-Alder transition state.