Development and Application of a Poly(ethylene glycol)-Supported Triarylphosphine Reagent:  Expanding the Sphere of Liquid-Phase Organic Synthesis

Abstract

Continuing studies into the utility of poly(ethylene glycol) (PEG)-supported triarylphosphines as functional polymer reagents in liquid-phase organic synthesis (LPOS) are being pursued. This report describes the synthesis and NMR characterization of an aryl-alkyl ether-linked PEG-triarylphosphine derivative (<b>2</b>) and its subsequent application in LPOS. The utility of <b>2</b> as a mild stoichiometric reagent for ozonide reduction has been demonstrated, and a direct comparison between <b>2</b>, a Merrifield resin-bound triarylphosphine derivative, and a solution-phase triphenylphosphine reagent revealed that the highest observed yields occur under liquid-phase conditions. Transformation of phosphine <b>2</b> into a phosphonium salt (<b>3</b>) then allowed the inherent aqueous solubility of PEG-functionalized moieties to be exploited by enabling a Wittig reaction, between a range of aldehydes and <b>3</b>, to occur under mildly basic aqueous conditions. This led to the generation of substituted stilbenes in good to excellent yields. Finally, regeneration of <b>2</b> was achieved by reduction of the PEG-supported triphenylphosphine oxide byproduct <b>4</b> with alane (100% conversion, 75% yield). This combination of reaction, recovery, and regeneration expands the utility of PEG-supported triarylphosphine reagents across the spectra of both organic chemistry and solution-phase combinatorial strategies.