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Synthesis 2007(15): 2240-2248  
DOI: 10.1055/s-2007-983800
PAPER
© Georg Thieme Verlag Stuttgart · New York

Synthesis and Cyclization of 3-Aryl-2-(arylacetoxy)acrylates: A Three-Step Access to Pulvinones

David Berniera, Frank Moserb, Reinhard Brückner*a
a Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstr. 21, 79104 Freiburg, Germany
b United Nations Environment Programme (UNEP), Chemicals Branch, DTIE, 11-13 chemin des Anémones, 1219 Châtelaine, Geneva, Switzerland
Fax: +49(761)2036100; e-Mail: reinhard.brueckner@organik.chemie.uni-freiburg.de;
Further Information

Publication History

Received 14 May 2007
Publication Date:
26 July 2007 (online)

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Abstract

(4-Methoxybenzyl)magnesium chloride was acylated with dialkyl oxalates 14a,b,d or S,S-di-tert-butyl dithiooxalate (14c) to give 2-hydroxy-3-(4-methoxyphenyl)acrylates and -thioacrylates 17a-d. Esterification with phenylacetic anhydride or (4-methoxyphenyl)acetic acid/N,N′-dicyclohexylcarbodiimide stereoselectively furnished 2-(arylacetoxy)-3-(4-methoxyphenyl)acrylates and thioacrylates (Z)-18a-d. Treating the latter with potassium tert-butoxide induced Dieckmann condensations, which led to isomerically pure pulvinones 1g,h in up to 88% yield.

Key words

3-arylpyruvate - Dieckmann condensation - enol ester - enolate fragmentation - fluorine-containing ester

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11

Type 8 compounds were obtained by the addition of substituted benzylmagnesium chlorides to the C≡N bond of the O-trimethylsilylated cyanohydrin of arylacetaldehydes, followed by hydrolysis (ref 10).

29

This is similarly observed if analogously formed ketenes are stabilized by a conjugated ester [28a] or cyano group. [28b]

31

The acceptor-substituted enolates derived from Weinstock’s esters 20 appear to be even more susceptible to the same kind of enolate fragmentation. This would be in line with the low yields of the resulting pulvinic esters (5-25%) and the occurrence of arylacetic acid and/or 2-aryl-3-hydroxy-maleates as byproducts. [21]