A Stereodivergent Synthesis of Enantiopure 3-Methoxypyrrolidines and 3-Methoxy-2,5-dihydropyrroles from 3,6-Dihydro-2H-1,2-oxazines

Robert Pulz; Toshiko Watanabe; Wolfgang Schade; Hans-Ulrich Reissig

doi:10.1055/s-2000-6654

Synlett 2000; 2000(7): 0983-0986
DOI: 10.1055/s-2000-6654

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A Stereodivergent Synthesis of Enantiopure 3-Methoxypyrrolidines and 3-Methoxy-2,5-dihydropyrroles from 3,6-Dihydro-2H-1,2-oxazines

Robert Pulz^* , Toshiko Watanabe, Wolfgang Schade, Hans-Ulrich Reissig

^*Institut für Chemie - Organische Chemie, Freie Universität Berlin, Takustr. 3, D-14195 Berlin, Germany; Fax + 49(0)30/8 38-5 53 67; E-mail: hans.reissig@chemie.fu-berlin.de

Abstract

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Hydrogenolysis of syn-3,4-dihydro-2H-1,2-oxazine (syn-2) in the presence of palladium on charcoal provided a diastereomeric mixture of amino alcohols 3a/3b from which pyrrolidine derivative 4a was obtained as major isomer after cyclization. Reduction with Raney-nickel furnished 3b and finally 4b as major components. The same stereodivergent behavior was found with the corresponding anti-1,2-oxazine (anti-2) giving either 3c and 4c or 3d and 4d as major isomers. These results are explained by a probably inverted order of reaction steps during the reductions. Less reactive Raney-nickel allowed isolation of intermediates 5a and 5b, which could be converted into 2,5-dihydropyrrole derivatives 6a and 6b respectively.

1,2-oxazine - hydrogenation - pyrrolidine - pyrrole

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