A Critical Overview of the Kabachnik-Fields Reactions Utilizing Trialkyl Phosphites in Water as the Reaction Medium: A Study of the Benzaldehyde-Benzylamine Triethyl Phosphite/Diethyl Phosphite Models

Dephosphinylative [4 + 2] Benzannulation of Phosphinyl Ynamines: Application to the Modular Synthesis of Polycyclic Aromatic Amines

A series of 9-amino-10-halophenanthrenes were synthesized through a one-pot process, including dephosphinylative Sonogashira-Hagihara coupling of 2-bromobiphenyls with air-stable phosphinyl ynamines, followed by halonium-promoted [4 + 2] benzannulation of the resulting 2-(aminoethynyl)biphenyls. Nonsubstituted and methyl-substituted 2-bromobiphenyls rapidly underwent the Sonogashira-Hagihara aminoethynylation and the halogenative Friedel-Crafts benzannulation to provide the corresponding amino(halo)phenanthrenes in high yields, while electron-sufficient and -deficient substrates did slowly undergo the former and the latter to result in low yields, respectively. This protocol worked well for the syntheses of highly π-extended aminophenanthrenes and aminobenzonaphthothiophenes with different optical properties. Further application of this approach between 2,2″- and 2',5'-dibromo-p-terphenyls with phosphinyl ynamines led to the regioselective formation of 6,13-diamino-5,12-dihalo- and 5,12-diamino-6,13-dihalo-dibenz[a,h]anthracenes via dual aminoethynylation and [4 + 2] benzannulation. The obtained analogues showed different ultraviolet-visible absorption and photoluminescence spectra with different emission quantum yields in CH₂Cl₂ solution and the powder state.

PMDTA-catalyzed multicomponent synthesis and biological activity of 2-amino-4H-chromenes containing a phosphonate or phosphine oxide moiety

A new approach for the preparation of (2-amino-3-cyano-4H-chromen-4-yl)phosphonate derivatives is described. The multicomponent reaction of salicylaldehydes, malononitrile and dialkyl phosphites catalyzed by pentamethyldiethylenetriamine (PMDTA) provided the bicyclic derivatives in high yields. The method developed did not require chromatographic separation, since the products could be recovered from the reaction mixture by simple filtration. Our approach made also possible condensation with secondary phosphine oxides, and this reaction has not been previously reported in the literature. The crystal structures of five derivatives were studied by single-crystal XRD analysis. The in vitro cytotoxicity on different cell lines and the antibacterial activity of the (2-amino-4H-chromen-4-yl)phosphonates synthesized were also explored. According to the IC50 values determined, several derivatives showed moderate or promising activity against mouse fibroblast (NIH/3T3) and human promyelocytic leukemia (HL-60) cells. Furthermore, three (2-amino-3-cyano-4H-chromen-4-yl)phosphine oxides were active against selected Gram-positive bacteria.

Green synthesis of α-aminophosphonates using ZnO nanoparticles as an efficient catalyst

Synthesis of α-aminophosphonate derivatives via the Kabachnik–Fields reaction is described using 1-(6-hydroxy-2-isopropenyl-1-benzofuran-yl)-1-ethanone, extracted from rhizomes of Petasites hybridus, primary amines and trialkyl phosphites in the presence of ZnO nanoparticles in water at room temperature. This procedure has advantages such as using natural products as precursors, employing water as a green solvent, good yields and easy separation of products.

Catalyst-free ultrasonic-promoted multicomponent synthesis of tertiary α-amino phosphonates

A highly efficient and green protocol has been developed for the synthesis of novel tertiary α-amino phosphonates via a catalyst-free multi-component Kabachnik–Fields reaction under ultrasound irradiation.