Silyl esters of phosphorous—common intermediates in synthesis

Copper-Catalyzed Cross-Coupling of Alkyl and Phosphorus Radicals for C(sp3)-P Bond Formation

A Cu^I-catalyzed cross-coupling of alkyl- and phosphorus-centered radicals for C(sp³)-P bond formation is introduced. Diacyl peroxides, generated in situ from aliphatic acids and H₂O₂, serve as a source for alkyl radicals and also an initiator for the generation of phosphorus radicals from H-P(O) compounds.

The Aryne-Abramov Reaction as a 1,2-Benzdiyne Platform for the Generation and Solvent-Dependent Trapping of 3-Phosphonyl Benzynes

Synthetic methodology utilizing two aryne intermediates (i.e., a formal benzdiyne) enables the rapid generation of structurally complex molecules with diverse functionality. This report describes the sequential generation of two ortho-benzyne intermediates for the synthesis of 2,3-disubstituted aryl phosphonates. Aryl phosphonates have proven useful in medicinal chemistry and materials science, and the reported methodology provides a two-step route to functionally dense variants by way of 3-phosphonyl benzyne intermediates. The process begins with regioselective trapping of a 3-trifloxybenzyne intermediate by an O-silyl phosphite in an Abramov-like reaction to bond the strained Csp carbons with phosphorus and silicon. Standard aryne-generating conditions follow to convert the resulting 2-silylphenyl triflate into a 3-phosphonyl benzyne, which readily reacts with numerous aryne trapping reactants to form a variety of 2,3-difunctionalized aryl phosphonate products. DFT computational studies shed light on important mechanistic details and revealed that 3-phosphonyl benzynes are highly polarizable. Specifically, the distortion in the internal bond angles at each of the Csp atoms was strongly influenced by both the electronegativity of the phosphonate ester groups as well as the dielectric of the computational solvation model. These effects were verified experimentally as the regioselectivity of benzyl azide trapping increased with more electronegative esters and/or increasingly polar solvents. Conversely, replacing the conventional solvent, acetonitrile, with nonpolar alternatives provided attenuated or even inverted selectivities. Overall, these studies showcase new reactivity of benzyne intermediates and extend the aryne relay methodology to include organophosphonates. Furthermore, this work demonstrates that the regioselectivity of aryne trapping reactions could be tuned by simply changing the solvent.

Controlled Synthesis of Polyphosphazenes with Chain-Capping Agents

N-alkyl phosphoranimines were synthesized via the Staudinger reaction of four different alkyl azides with tris(2,2,2-trifluoroethyl) phosphite. N-adamantyl, N-benzyl, N-t-butyl, and N-trityl phosphoranimines were thoroughly characterized and evaluated as chain-capping compounds in the anionic polymerization of P-tris(2,2,2-trifluoroethoxy)-N-trimethylsilyl phosphoranimine monomer. All four compounds reacted with the active chain ends in a bulk polymerization, and the alkyl end groups were identified by 1H-NMR spectroscopy. These compounds effectively controlled the molecular weight of the resulting polyphosphazenes. The chain transfer constants for the monomer and N-benzyl phosphoranimine were determined using Mayo equation.

Phosphorus-Containing Fluoropolymers: State of the Art and Applications

Several strategies to synthesize fluorinated (co)polymers containing phosphorus groups and their applications are reviewed. First, original fluoromonomers bearing phosphorus atoms are supplied from relevant routes. They may possess fluorinated atoms linked to the ethylenic carbon atoms with different structures, such as F₂C═CF- or H₂C═C(CF₃)- and a phosphonated ω-function adjacent to an aliphatic or aromatic linker, while other monomers display a difluoromethylene dialkylphosphonate end group such as -CF₂-P(O)(OR)₂. Then, fluorinated copolymers were obtained according to various pathways: (i) by radical homopolymerization of monomers containing both fluorine and phosphorus atoms, (ii) by direct radical copolymerization of fluoromonomers and phosphorus-based monomers, or (iii) by chemical modification of fluorinated copolymers with phosphorus-based reactants. Conventional radical and controlled (or reversible deactivation radical polymerization, RDRP) copolymerization have also been explored. As for the chemical change of halogenated polymers, either conventional organic reactions (e.g., Arbuzov reaction from a chlorine, iodine, or bromine atom) or radiation grafting with specific monomers led to graft copolymers composed of a fluorinated backbone and phosphonated grafts. This second part also details aliphatic and aromatic fluorophosphorous copolymers in which dialkylphosphonates or phosphonic acids are reported. Finally, since fluorine and phosphorus atoms bring complementary relevant properties (low refractive index and dielectric constants, chemical inertness, high electrochemical, soils, and heat resistances, electroattractivity from fluorine atoms and high acidity, complexation, anticorrosion, flame retardant, and biomedical properties from phosphorus ones), synergetic characteristics have been targeted. These properties allow such fluoro-phosphorus (co)polymers to be used as novel materials involved in various applications such as polymer exchange membranes for fuel cells, self-etching adhesives for dental materials, adhesion promoters, flame retardants, polymer blends, and anticorrosive coatings.

Chemical Synthesis of (RP)- and (SP)-[16O,17O,18O]Phosphoenol Pyruvate

Enzymes and chirality are intimately associated. For their mechanisms to be studied, chiral substrates are needed as probes. Here, we report a concise synthesis of (R_P)- and (S_P)-[¹⁶O,¹⁷O,¹⁸O]phosphoenol pyruvate starting from enantiomerically pure (R)-2-chloro-1-phenylethanol, which was transformed into ¹⁸O-labeled 3-methyl-1-phenylbutane-1,3-diol. The diol was reacted with tris(dimethylamino)phosphane and consecutively with H₂¹⁷O to yield a mixture of cyclic H-phosphonates labeled with ¹⁷O and ¹⁸O. They were silylated and subjected to a Perkow reaction with ethyl 3-chloropyruvate. Two protected-[¹⁶O,¹⁷O,¹⁸O]phosphoenol pyruvates were formed and finally globally deprotected. Their configuration was reassessed by a known enzymatic test in combination with conversion of the formed d-glucose-6-phosphate into mixtures of labeled methyl d-glucose-4,6-phosphates, which were analyzed by ³¹P NMR spectroscopy. The enzymatic test supported the configuration assigned to labeled stereogenic phosphorus atoms on the basis of synthesis.

Triazole-Based Anion-Binding Catalysis for the Enantioselective Dearomatization of N-Heteroarenes with Phosphorus Nucleophiles

The first enantioselective synthesis of chiral heterocyclic α-amino phosphonates by nucleophilic dearomatization of quinolines and pyridines using an anion-binding organocatalysis approach is described. Chiral tetrakistriazoles were employed as efficient hydrogen-bond donor catalysts by forming a chiral close ion-pair with the in situ formed N-acyl salts and 2,2,2-trichlorethoxycarbonyl chloride (TrocCl). The ion-pair was subsequently treated with various phosphorus nucleophiles, such as silyl-protected dialkyl- and trialkylphosphites. Thus, the corresponding products were obtained in complete or high regioselectivities and up to 97:3 e.r. for quinolines or up to 89:11 e.r. for the more challenging pyridine substrates. This method allows for rapid access to substituted chiral cyclic α-amino phosphonates, which can be easily transformed into phosphonic acid derivatives.

Enantioselective dearomatization of isoquinolines by anion-binding catalysis en route to cyclic α-aminophosphonates

An enantioselective dearomatization of isoquinolines has been developed using chiral anion-binding catalysis. This transformation makes use of silyl phosphite as a nucleophile and generates cyclic α-aminophosphonates.

An enantioselective dearomatization of isoquinolines has been developed using chiral anion-binding catalysis. This transformation, catalyzed by a simple and easy to prepare tert-leucine-based thiourea derivative, makes use of silyl phosphite as a nucleophile and generates cyclic α-aminophosphonates. This is the first time asymmetric anion-binding catalysis has been applied to the synthesis of α-aminophosphonates.

The catalytic asymmetric Abramov reaction

The first catalytic enantioselective Abramov reaction is described. The process is based on the utilization of a chiral disulfonimide catalyst, which efficiently avoids the difficulties encountered with metal-based catalysts. Several functionalized α-hydroxy phosphonates were synthesized in good yields and with excellent enantiomeric ratios of up to >99:1. The process was shown to be scalable and up to 1 g of starting material could be employed under mild reaction conditions.