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

J Org Chem. 1999 Jul 9;64(14):5188-5192. doi: 10.1021/jo9903712.

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 (2) and its subsequent application in LPOS. The utility of 2 as a mild stoichiometric reagent for ozonide reduction has been demonstrated, and a direct comparison between 2, 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 2 into a phosphonium salt (3) then allowed the inherent aqueous solubility of PEG-functionalized moieties to be exploited by enabling a Wittig reaction, between a range of aldehydes and 3, to occur under mildly basic aqueous conditions. This led to the generation of substituted stilbenes in good to excellent yields. Finally, regeneration of 2 was achieved by reduction of the PEG-supported triphenylphosphine oxide byproduct 4 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.