The Synthesis and Mechanistic Considerations of a Series of Ammonium Monosubstituted H-Phosphonate Salts

A series of ammonium monosubstituted H-phosphonate salts were synthesized by combining H-phosphonate diesters with amines in the absence of solvent at 80 °C. Variation of the ester substituent and amine produced a range of ionic liquids with low melting points. The products and by-products were analyzed by spectroscopic and spectrometric techniques in order to get a better mechanistic picture of the dealkylation and formal dearylation observed. For dialkyl H-phosphonate diesters, (RO)₂ P(O)H (R=alkyl), the reaction proceeds via direct dealkylation with the reactivity increasing in the order R=iPr<Et<Me corresponding to DFT calculated activation enthalpies of 22.6, 20.8, and 17.9 kcal mol^-1 . For the diphenyl H-phosphonate diesters, (PhO)₂ P(O)H, the dearylation was found to proceed via phenol-assisted formation of a 5-coordinate intermediate, (PhO)₃ PH(OH), from which P(OPh)₃ and water were eliminated. The presence of an equivalent of water then facilitated the formation of P(OH)₂ OPh and the amine, R'NH₂ , subsequently abstracted a proton from it to yield [(PhO)PH(O)O]^- [R'NH₃ ]⁺ .

Recent trends in the direct oxyphosphorylation of C-C multiple bonds

Due to the wide importance of β-phosphorylated ketones as key building-blocks in the fabrication of various pharmaceutically active organophosphorus compounds, finding new and truly efficient methods for their preparation from simple, low-cost and ubiquitous feedstock materials within a single click is an interesting subject in organic synthesis. Recently, oxyfunctionalization of carbon-carbon multiple bonds has arisen as a straightforward and versatile tool for the synthesis of complex organic molecules from the simple and easily accessible alkenes/alkynes via a single operation. In this context, oxyphosphorylation of alkenes/alkynes with P(O)-H compounds has attracted considerable attention as a unique procedure for the construction of β-phosphorylated ketones. In this review, we outline the recent advances and developments in this fast-growing research field with particular emphasis on the mechanistic aspects of reaction.

Cross-Dehydrogenative Alkynylation: A Powerful Tool for the Synthesis of Internal Alkynes

Alkynes are among the most fundamentally important organic compounds and are widely used in synthetic chemistry, biochemistry, and materials science. Thus, the development of an efficient and sustainable method for the preparation of alkynes has been a central concern in organic synthesis. Cross-dehydrogenative coupling utilizing E-H and Z-H bonds in two different molecules can avoid the need for prefunctionalization of starting materials and has become one of the most straightforward methods for the construction of E-Z chemical bonds. This Review summarizes recent progress in the preparation of internal alkynes by cross-dehydrogenative coupling with terminal alkynes.