Wittig Reagents Bound to Cross-Linked Polystyrenes

Article abstract of DOI:10.1021/jo00151a010

Insoluble benzyltriarylphosphonium and methyltriarylphosphonium salts have been prepared on 2percent and 8percent divinylbenzene cross-linked polystyrene and on 20percent divinylbenzene cross-linked macroporous polystyrene.Phosphoranes were generated with sodium methoxide or sodium ethoxide in THF and with the dimethylsulfinyl carbanion in Me2SO from the benzyl- and methylphosphonium salts, respectively.Reactions of the phosphoranes with a variety of aldehydes and ketones provided alkenes in 73-96percent yields (by GLC analysis) with the 2percent cross-linked polymer, 52-77percent yields with the 8percent cros s-linked polymer, and 72-87percent yields with the 20percent cross-linked macroporous polymer.The rates of phosphorane generation and alkene formation depend on the polymer, decreasing in the order 2percent > 20percent macroporous > 8percent cross-linked.The fraction of E double bond product from the benzylphosphonium salt and either benzaldehyde or cinnamaldehyde is greater with the 20percent cross-linked macroporous polymer than with the 2percent cross-linked polymer.The byproduct polymer-bound phosphine oxides were reduced to phosphines with trichlorsilane, and the phosphines were reused for Wittig synthesis.A quantitative 31P-NMR analysis of phosphine and phosphine oxide residues in polystyrene gels is reported.