Functionalization of Intact Trimetaphosphate: A Triphosphorylating Reagent for C, N, and O Nucleophiles

Abstract

Trimetaphosphate (TriMP, [P₃O9]³⁻) reacts with PyAOP ([(H₈C₄N)₃PON₄C₅H₃][PF₆]) to yield an activated TriMP, [P₃O₉P(NC₄H₈)₃]⁻ (1), incorporating a phosphonium moiety. Anion 1 is isolated as its bis(triphenylphosphine)iminium (PPN) salt in 70% yield and phosphorylates nucleophiles with elimination of phosphoramide OP(NC₄H₈)₃. Treatment of 1 with amines HNR¹R² generates [P₃O₈NR¹R²]²⁻(2a: R¹ = R² = Et; 2b: R¹ = H, R² = tBu) in greater than 70% yield as mixed PPN and alkyl ammonium salts. Treatment of 1 with primary alcohols in the presence of a tertiary amine base results in salts of intact TriMP alkyl esters [P₃O₉R]²⁻(3a: R = Me; 3b: R = Et) in greater than 60% isolated yield. Reaction of 1 with [PPN][H₂PO4] provides orthophosphoryl TriMP (4, [P₄O1₂H₂]²⁻) in 40% yield as the PPN salt. Treatment of 1 with Wittig reagent H₂CPPh₃ (4 equiv) provides phosphorus ylide [P₃O₈CHPPh₃]²⁻ (5) in 61% yield as a mixed salt. Ylide 5 reacts with water to provide [P₃O₈Me]²⁻(6) and with aldehydes to give olefins [P₃O₈CHCHR]²⁻ (7a: R = H; 7b: R = 4-C₆H₄Br), products in which one TriMP oxygen is replaced by a phosphonate P–C linkage. Treatment of intact TriMP derivatives 2a, 2b, 3a, and 7a with aqueous tetrabutylammonium hydroxide results in ring opening to linear triphosphate derivatives. X-ray crystal structures are provided for salts of 1, 2a, 3a, and 4.