Sigmatropic isomerizations in azaallyl systems: XX. N-Alkylbenzimidoylphosphonates

Practical Synthesis of Chiral α-Aminophosphonates with Weak Bonding Organocatalysis at ppm Loading

α-Aminophosphonic acids as an important class of bioisosteres of α-amino acids demonstrate various biologically important activities. We report here the development of a highly enantioselective isomerization of α-iminophosphonates enabled by an extraordinarily efficient organocatalyst. This organocatalyst afforded a total turnover number (TON) of 20,000-1,000,000 for a wide range of α-alkyl iminophosphonates. Even at a parts-per-million (ppm) loading, this catalyst achieved a complete reaction in greater than 93% enantiomeric excess (ee). Computational studies revealed that this small-molecule catalyst achieved enzyme-like efficiency via a network of weak bonding interactions that effectively preorganized the substrate and catalyst toward a transition-state-like complex. Considering the substrate tolerance, catalytic efficiency, and mechanism, this organocatalyst could be regarded as a small-molecule isomerase.

Deoxygenative Nucleophilic Phosphonation and Electrophilic Alkylation of Secondary Amides: A Facile Access to Quaternary α-Aminophosphonates

The widespread occurrence and synthetic accessibility of amides render them valuable precursors for the synthesis of diverse nitrogen-containing compounds. Herein, we present a metal-free and streamlined synthetic strategy for the synthesis of quaternary α-aminophosphonates. This approach involves sequential deoxygenative nucleophilic phosphonation and versatile electrophilic alkylation of secondary amides in a one-pot fashion. Notably, this method enables the direct bis-functionalization of secondary amides with both nucleophiles and electrophiles for the first time, with simple derivatization leading to valuable free α-aminophosphonates by hydrolysis. The protocol has the advantages of operational simplicity, broad functional-group compatibility, environmental friendliness, and scalability to multigram quantities.