Sulfated polyborate catalyzed Kabachnik-Fields reaction: An efficient and eco-friendly protocol for synthesis of α-amino phosphonates

X-ray Structure Determination of Naphthalen-2-yl 1-(Benzamido(diethoxyphosphoryl)methyl)-1H-1,2,3-triazole-4-carboxylate

We have previously published on a new triazolic phosphonic α-amino ester in position 4 on the triazole ring of a naphthalene ester. The aim of the present paper was to describe its crystallographic study by XRD. The crystal structure of naphthalen-2-yl 1-(benzamido(diethoxyphosphoryl)methyl)-1H-1,2,3-triazole-4-carboxylate was determined by single-crystal X-ray diffraction. This compound crystallizes in the monoclinic system, space group P21/c. The naphthalene system is almost planar and makes dihedral angles of 67.1(2)° and 63.9(2)° with the triazole ring and the phenyl cycle, respectively. The phosphorus atom is surrounded by three oxygen atoms and one carbon atom building a distorted tetrahedron. It is also noted, that one of the two ethyl groups is disordered. In the crystal, the molecules are connected through C-H…O and N-H…O hydrogen bonds to build dimers that are linked together by C-H…O hydrogen bonds, in addition to C-H…π interactions. The presence of an intramolecular hydrogen bond contributes to the stability of the molecular conformation by completing the S(5) cycle.

Synthesis of α-Aminophosphonates and Related Derivatives; the Last Decade of the Kabachnik-Fields Reaction

The Kabachnik-Fields reaction, comprising the condensation of an amine, oxo compound and a P-reagent (generally a >P(O)H species or trialkyl phosphite), still attracts interest due to the challenging synthetic procedures and the potential biological activity of the resulting α-aminophosphonic derivatives. Following the success of the first part (Molecules 2012, 17, 12821), here we summarize the synthetic developments in this field accumulated in the last decade. The procedures compiled include catalytic accomplishments as well as catalyst-free and/or solvent-free "greener" protocols. The products embrace α-aminophosphonates, α-aminophosphinates, and α-aminophosphine oxides along with different bis derivatives from the double phospha-Mannich approach. The newer developments of the aza-Pudovik reactions are also included.

The synthesis of HMF-based α-amino phosphonatesviaone-pot Kabachnik–Fields reaction

The first use of biomass-derived HMF in the one-pot Kabachnik–Fields reaction is reported here. A wide range of furan-based α-amino phosphonates were prepared in moderate to excellent yields under mild, effective and environmentally-benign conditions: iodine as a non-metal catalyst, biobased 2-MeTHF as the solvent and room or moderate temperature. The hydroxymethyl group of HMF persists in the Kabachnik–Fields products, widening the scope of further modification and derivatization compared to those arising from furfural. Issues involving the diastereoselectivity and double Kabachnik–Fields condensation were also faced.

A mild and efficient one-pot protocol for the synthesis of α-amino phosphonates directly from 5-HMF was described.