Mechanistic Insights into the Palladium(II)‐catalyzed Intramolecular Cyclization of o‐Alkynylphenylphosphonamide and N‐(o‐Alkynylphenyl)acetamide by Electrospray Ionization Mass Spectrometry

Abstract

The intramolecular cyclization of o-alkynylphenylphosphonamide and N-(o-alkynylphenyl)acetamide was monitored by electrospray ionization mass spectrometry (ESI-MS) and its tandem version (ESI-MS/MS). The proposed intermediates were successfully intercepted and characterized. In addition, the intermediates composed of the substrate coordinated to the palladium(II) center in the reaction of o-alkynylphenylphosphonamide were unexpected before, and this interesting phenomenon of the substrate coordination seems associated with the unique structure of substrates.

Late Transition Metal-Catalyzed Hydroamination and Hydroamidation

“…The 6- endo -dig cyclization products are selectively obtained also in the palladium-catalyzed intramolecular hydroamidation of N -alkyl- o -ethynylbenzamides reported by Sashida et al (Scheme ) . The same catalyst was also able to convert the structurally related phosphonamides under slightly modified conditions (Scheme ). , …”

“…454 The same catalyst was also able to convert the structurally related phosphonamides under slightly modified conditions (Scheme 94). 455,456 In the hydroamidation of o-alkynylbenzyl carbamates by Catalań et al, a clear substrate dependence of the endo/exo selectivity of the cyclization step was observed (Scheme 95). 457,458 With gradually increasing numbers of α-fluorine atoms, the ratio of 5-exo to 6-endo cyclization was shifted from 40:60 for CH 3 to 80:20 for CF 3 .…”

The application of electrospray ionization mass spectrometry to homogeneous catalysis

“…Peaks were observed corresponding to allyl-type intermediates such as Some less common Pd-catalyzed bond-forming reactions have been investigated as well, including tellurium-carbon bond formation (ionized by loss of halide) [14], intramolecular nitrogen-carbon bond formation (ionized by association of H + or Na + ) [67], and the formation of two new carbon-oxygen bonds in the hydroxyalkoxylation of 2-allylphenols (ionized by loss of H + in the negative-ion mode, and loss of an anionic ligand or association of Na + in positive-ion mode) [68]. A study by Guo et al determined the mechanism of a palladium-catalyzed three-component cyclization reaction (the formation of cispyrolidine derivatives from imine, iodobenzene and 2-(2,3-allenyl)malonate) [69].…”