Synthesis of Acyl Phosphoramidates Employing a Modified Staudinger Reaction

CuH-Catalyzed Reductive Coupling of Nitroarenes with Phosphine Oxides for the Direct Synthesis of Phosphamides

A CuH-catalyzed reductive coupling of nitroarenes with phosphine oxides is developed, which produces a series of phosphamides in moderate to excellent yields with good functional group tolerance. Gram-scale synthesis and late-stage modification of nitro-aromatic functional molecule niclosamide are also successfully conducted. The mechanism study shows that the nitro group is transformed after being reduced to nitroso and a nucleophilic addition procedure is involved during the reaction.

Electrochemical Oxidative Sulfonylation-Azidation of Alkenes

A novel electrochemical oxidative sulfonylation-azidation of alkenes is accomplished by using sulfonyl hydrazide and trimethylsilyl azide (TMSN3) for the one-pot and green synthesis of β-azidoarylsulfone, which involves the direct construction of new C-S and C-N bonds. Notably, neither exogenous oxidants/additives nor metal catalysts are required for this method. In addition, this electrochemical strategy features mild conditions and wide substrate scope and has been proved to be a radical pathway by mechanistic studies.

Tf2O-Mediated P(O)-N Bond Formation of Either P(O)-OH or P(O)-H Reagents with Multitype Amines

We have developed a Tf2O-mediated approach for the direct amination of either P(O)-OH or P(O)-H reagents with a variety of aliphatic or aromatic amines. Without the requirement of precious metals and toxic reagents, this protocol provides an alternative route to various phosphinamides and phosphoramides. The reaction proceeds under simple and mild conditions and can be effectively scaled up with similar efficiency.

Chemoselective Staudinger Reactivity of Bis(azido)phosphines Supported with a π-Donating Imidazolin-2-iminato Ligand

Synthesis and characterization of new P(III) and P(V) bis(azido)phosphines/phosphoranes supported by an N,N'-bis(2,6-diisopropylphenyl) imidazolin-2-iminato (IPrN) ligand and their reactivity with various secondary and tertiary phosphines result in the formation of chiral and/or asymmetric mono(phosphinimino)azidophosphines via the Staudinger reaction. The reaction of IPrNP(N3)2 (2) or IPrNP(S)(N3)2 (4S) with an excess of tertiary phosphine resulted in the chemoselective formation of IPrNP(N3)(NPMe3) (7) or IPrNP(S)N3(NPR3) (5R), respectively. The chemoselective Staudinger reactivity was also observed in reactions using a secondary phosphine (HPCy2) to produce IPrNP(S)N3[NP(H)Cy2] (6a), which exists in equilibrium with a tautomeric IPrNP(S)N3[N(H)PCy2] form (6b), as confirmed by 31P-31P nuclear Overhauser effect spectroscopy (NOESY). Density functional theory (DFT) calculations point to a combination of energetically unfavorable lowest unoccupied molecular orbitals (LUMOs) and the accumulation of increasing negative charge at the terminal azido-nitrogen upon a single azide-to-phosphinimine conversion that gave rise to the observed chemoselectivity.

Chemodivergent Staudinger Reactions of Secondary Phosphine Oxides and Application to the Total Synthesis of LL-D05139β Potassium Salt

Unprecedented Staudinger reaction modes of secondary phosphine oxides (SPO) and organic azides are herein disclosed. By the application of various additives, selective nitrogen atom exclusion from the azide group has been achieved. Chlorotrimethylsilane mediates a stereoretentive Staudinger reaction with a 2-N exclusion which provides a valuable method for the synthesis of phosphinic amides and can be considered complementary to the stereoinvertive Atherton-Todd reaction. Alternatively, a 1-N exclusion pathway is promoted by acetic acid to provide the corresponding diazo compound. The effectiveness of this protocol has been further demonstrated by the total synthesis of the diazo-containing natural product LL-D05139β, which was prepared as a potassium salt for the first time in 6 steps and 26.5 % overall yield.

Copper-cobalt double metal cyanides as green catalysts for phosphoramidate synthesis

Phosphoramidates are common and widespread backbones of a great variety of fine chemicals, pharmaceuticals, additives and natural products. Conventional approaches to their synthesis make use of toxic chlorinated reagents and intermediates, which are sought to be avoided at an industrial scale. Here we report the coupling of phosphites and amines promoted by a Cu₃[Co(CN)₆]₂-based double metal cyanide heterogeneous catalyst using I₂ as additive for the synthesis of phosphoramidates. This strategy successfully provides an efficient, environmentally friendly alternative to the synthesis of these valuable compounds in high yields and it is, to the best of our knowledge, the first heterogeneous approach to this protocol. While the detailed study of the catalyst structure and of the metal centers by PXRD, FTIR, EXAFS and XANES revealed changes in their coordination environment, the catalyst maintained its high activity for at least 5 consecutive iterations of the reaction. Preliminary mechanism studies suggest that the reaction proceeds by a continuous change in the oxidation state of the Cu metal, induced by a O₂/I^- redox cycle.

Tris(4-azidophenyl)methanol - a novel and multifunctional thiol protecting group

The novel tris(4-azidophenyl)methanol, a multifunctionalisable aryl azide, is reported. The aryl azide can be used as a protecting group for thiols in peptoid synthesis and can be cleaved under mild reaction conditions via a Staudinger reduction. Moreover, the easily accessible aryl azide can be functionalised via copper-catalysed cycloaddition reactions, providing additional opportunities for materials chemistry applications.

Continuous Flow Generation of Acylketene Intermediates via Nitrogen Extrusion

A flow chemistry process for the generation and use of acylketene precursors through extrusion of nitrogen gas is reported. Key to the development of a suitable continuous protocol is the balance of reaction concentration against pressure in the flow reactor. The resulting process enables access to intercepted acylketene scaffolds using volatile amine nucleophiles and has been demonstrated on the gram scale. Thermal gravimetric analysis was used to guide the temperature set point of the reactor coils for a variety of acyl ketene precursors. The simultaneous generation and reaction of two reactive intermediates (both derived from nitrogen extrusion) is demonstrated.

Cutting edge of diphenyl phosphorazidate (DPPA) as a synthetic reagent – A fifty-year odyssey

Recent developments of diphenyl phosphorazidate (DPPA, (C6H5O)2P(O)N3) has been reviewed.