Development and application of a poly(ethylene glycol)-supported triarylphosphine reagent: Expanding the sphere of liquid-phase organic synthesis

Continuing studies into the utility of poly(ethylene glycol) (PEG)-supporte d 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 de rivative (2) and its subsequent application in LPOS. The utility of 2 as a mild stoichiometric reagent for ozonide reduction has been demonstrated, an d a direct comparison between 2, a Merrifield resin-bound triarylphosphine derivative, and a solution-phase triphenylphosphine reagent revealed that t he highest observed yields occur under liquid-phase conditions. Transformat ion of phosphine 2 into a phosphonium salt (3) then allowed the inherent aq ueous solubility of PEG-functionalized moieties to be exploited by enabling a Wittig reaction, between a range of aldehydes and 3, to occur under mild ly basic aqueous conditions. This led to the generation of substituted stil benes in goad 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 re agents across the spectra of both organic chemistry and solution-phase comb inatorial strategies.