Synthesis 2008(13): 2023-2032  
DOI: 10.1055/s-2008-1067102
PAPER
© Georg Thieme Verlag Stuttgart · New York

Development of a Tandem Base-Catalyzed, Triphenylphosphine-Mediated Disulfide Reduction-Michael Addition

Alessandra Bartolozzi*, Hope M. Foudoulakis, Bridget M. Cole
Surface Logix, Inc., 50 Soldiers Field Place, Brighton, MA 02135, USA
Fax: +1(617)7838877; e-Mail: abartolozzi@surfacelogix.com;
Further Information

Publication History

Received 20 February 2008
Publication Date:
21 May 2008 (online)

Abstract

A tandem disulfide reduction-Michael addition was developed using both free and polymer-bound triphenylphosphine as the reducing agent. The procedure was applied to intermolecular systems for the synthesis of arylsulfanyl- and alkylsulfanyl-substituted propanoates and related ketones, and to an intramolecular system for the synthesis of a benzothiazepinone derivative.

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The 1H NMR spectra of the isolated products confirmed the presence of a free hydroxy group as we would expect for compounds derived by thiol addition. The thiol moiety of 4-sulfanylphenol is the strongest and the most-reactive nucleophile in the compound as it has a pK a of 6.8 compared with the hydroxy group pK a of 12.4. However, the phenol is still a reactive species that could possibly undergo Michael addition under basic conditions if the disulfide reduction was too slow and the more-reactive thiol was not formed quickly enough. To confirm that the disulfide reduction occurred first in our protocol and that side products derived from a phenol addition were not formed, we repeated the experiment reported in entry 1 of Table [1] without adding triphenylphosphine. In this case, phenol addition was not observed, even after heating the reaction overnight.

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1H NMR spectra in accordance with data reported in the Wiley Subscription Services Inc., USA.