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. 2014 Jul 28;20(31):9762-9.
doi: 10.1002/chem.201402684. Epub 2014 Jul 2.

Stereodivergent organocatalytic intramolecular Michael addition/lactonization for the asymmetric synthesis of substituted dihydrobenzofurans and tetrahydrofurans

Dorine Belmessieri  1 , Alix de la Houpliere, Ewen D D Calder, James E Taylor, Andrew D Smith
Affiliations

Stereodivergent organocatalytic intramolecular Michael addition/lactonization for the asymmetric synthesis of substituted dihydrobenzofurans and tetrahydrofurans

Dorine Belmessieri et al. Chemistry. .

Abstract

A stereodivergent asymmetric Lewis base catalyzed Michael addition/lactonization of enone acids into substituted dihydrobenzofuran and tetrahydrofuran derivatives is reported. Commercially available (S)-(-)-tetramisole hydrochloride gives products with high syn diastereoselectivity in excellent enantioselectivity (up to 99:1 d.r.syn/anti , 99 % eesyn ), whereas using a cinchona alkaloid derived catalyst gives the corresponding anti-diastereoisomers as the major product (up to 10:90 d.r.syn/anti , 99 % eeanti ).

Keywords: Michael addition; asymmetric catalysis; cinchona alkaloid; isothiourea; organocatalysis; oxygen heterocycles; stereodivergent.

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Figures

Scheme 1
Scheme 1
Intramolecular Michael addition/lactonization for the synthesis of syn-2,3-dihydrobenzofurans catalyzed by a) cinchona alkaloid derivative 2;[6a] b) (S)-(−)-tetramisole hydrochloride 5.[9j] c) Proposed stereodivergent synthesis of 2,3-dihydrobenzofuran, 2,3-THF, and 3,4-THF derivatives.
Scheme 2
Scheme 2
Unsuccessful intramolecular Michael addition/lactonization for the synthesis of anti-2,3-THFs.
Scheme 3
Scheme 3
a) Proposed mechanism for Lewis-base (LB*)-catalyzed Michael addition/lactonization of activated enone acids into 2,3-dihydrobenzofurans. b) Proposed pretransition state assembly by using (S)-(−)-tetramisole hydrochloride 5 as catalyst. c) Proposed pretransition state assembly by using OTMS-quinidine 19 catalyst.
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