Reaction of Triphenylphosphine Radical Cation with 1, 3-Dicarbonyl Compounds : Electrochemical One-Step Preparation of Dioxomethylenetriphenylphosphoranes

Abstract

Electrochemical oxidation of Ph₃P (1) in MeCN in the presence of 1, 3-dicarbonyl compounds, R¹COCH₂COR² (3), with HCIO₄ as the supporting electrolyte resulted in the formation of the phosphonium salts, Ph₃P⁺-CH(COR¹)COR² ClO₄^- (4), provieded that R¹ and/or R² is a phenyl group. On the other hand, electrolysis in CH²Cl² with 2, 6-lutidinium perhlorate gave the phosphoranes, Ph₃P=C(COR¹)COR² (5), directly from 1 and 3 in fair to excellent yields : in this case, R¹ or R² need not necessarily be a phenyl group. Thus, the electrolysis is shown to be a convenient method to perpare 5 in a single step. Plausible processes for the formation of 4 and 5 are proposed, involving the reaction of electrochemically generated Ph₃P⁺·with the enol form of 3 as the keystep.