Synthesis and characterization of two bifunctional pyrazole-phosphonic acid ligands

The bifunctional compounds 3,5-dimethyl-4-(4-phosphonophenyl)-1H-pyrazole 1 and 4-(4-phosphonophenyl)-1H-pyrazole 2 were synthesized via Suzuki-Miyaura coupling, starting from a Boc-protected pyrazolylboronic acid ester and the iodoarylphosphonate. The target compounds were isolated after acidic hydrolysis in the form of the hydrochloride salts 1 · HCl and 2 · HCl · H2O with a yield of 81% and 86%, respectively. Pd(dppf)Cl2 was found to be superior to Pd(PPh3)4 as a catalyst; dry 1,4-dioxane as a solvent, Cs2CO3 as a base, and no co-ligands were the best found conditions. The alternative routes through iodoarylphosphonate of iodoarylpyrazole, with the crucial steps based on the copper-catalyzed coupling with acetylacetone or the Arbuzov reaction were proven inefficient. The structures of the isolated hydrochloride salts 1 · HCl and 2 · HCl · H2O feature hydrogen-bonded networks involving the chloride anions.

Microwave irradiation and catalysis in organophosphorus reactions

The usual advantage of microwave (MW) assistance is making organic reactions faster and more efficient. In this article we present reaction types from organophosphorus chemistry, when MW-assisted transformations (e.g. the direct esterification and alkylating esterification of phosphinic acids) may be promoted by suitable catalysts, or vice versa, when a catalytic reaction is enhanced by MW irradiation (e.g. the Arbuzov reaction of aryl halides), and when catalysts may be omitted or simplified under MW irradiation as shown by the alkylation of active methylene containing P=O substrates/the Kabachnik–Fields reaction/deoxygenation of phosphine oxides, and the Hirao reaction, respectively.

Diversion of the Arbuzov reaction: alkylation of C–Cl instead of phosphonic ester formation on the fullerene cage

We report an “inversed” Arbuzov reaction of C60Ar5Cl with P(OR)3 producing C60Ar5R with an excellent selectivity.

Synthesis of Phosphonates via Michaelis-Arbuzov Reaction

Background: Michaelis–Arbuzov reaction has played a key role for the synthesis of dialkyl or diaryl phosphonates by reacting various alkyl or aryl halides with trialkyl or triaryl phosphite. This reaction is very versatile in the formation of P-C bond from the reaction of aliphatic halides with phosphinites or phosphites to yield phosphonates, phosphinates, phosphine oxides. The Arbuzov reaction developed some methodologies, possible mechanistic pathways, selectivity, potential applications and biologically active various phosphonates. Objective: The synthesis of phosphonates via Michaelis–Arbuzov reaction with many new and fascinating methodologies were developed and disclosed in the literature, and these are explored in this review. Conclusion: This review has discussed past developments and vast potential applications of Arbuzov reaction in the synthesis of organophosphonates. As presented in this review, various synthetic methodologies were developed to prepare a large variety of phosphonates. Improvements in the reaction conditions of Lewis-acid mediated Arbuzov rearrangement as well as the development of MW-assisted Arbuzov rearrangement were discussed. Finally, to achieve high selectivities and yields, fine-tuning of reaction conditions including solvent type, temperature, and optimal reaction times to be considered.