[73473-51-5]  · C9H18NO3P  · N-Ethyl(diethoxyphosphinyl)methylketenimine  · (MW 219.25)

(ketenimine functionalized with a diethoxyphosphinyl group;1 reacts with nucleophiles to give various phosphonates; an annulation reagent for the synthesis of heterocycles)

Physical Data: bp 86-90 °C/1 mmHg.

Form Supplied in: colorless liquid.

Analysis of Reagent Purity: IR: nC=C=N 2030 cm-1.

Preparative Method: synthesized in 82% yield by the dehydration of diethyl (N-ethylcarbamoylethyl)phosphonate, which is prepared from N-ethyl-a-chloropropionamide and diethyl sodiophosphite (eq 1).

Handling, Storage, and Precautions: use in a fume hood.

Reaction with Nucleophiles and Use as an Annulation Reagent.2

Nucleophilic addition of ethanol, diethylamine, or hydrazoic acid to the title ketenimine (1) gives the imidate, amidine, or tetrazole with a phosphonyl residue, respectively, showing typical reactivity of ketenimines (eq 2).

The reactions of (1) with sodium salts of salicylaldehyde, o-hydroxyacetophenone, a-formyl-b-naphthol, 2-formylpyrrole, and 2-acetylpyrrole in DMF give benzopyrans, naphthopyrans, and pyrrolizines with exocyclic imine groups (eqs 3 and 4). These annulation reactions occur via initial nucleophilic attack of the anionic species at the center carbon of the ketenimine followed by the intramolecular Horner-Emmons reaction as seen in the tandem Michael-Horner-Emmons reaction of vinylphosphonates.3

Related Reagents.

Trimethyl 2-Phosphonoacrylate; Tris(trimethylsilyl)ketenimine.

1. Motoyoshiya, J.; Enda, J.; Ohshiro, Y.; Agawa, T. CC 1979, 900.
2. Motoyoshiya, J.; Teranishi, A.; Mikoshiba, R.; Yamamoto, I.; Gotoh, H.; Enda, J.; Ohshiro, Y.; Agawa, T. JOC 1980, 45, 5385.
3. Minami, T.; Motoyoshiya, J. S 1992, 333.

Yoshiki Ohshiro

Osaka University, Japan

Jiro Motoyoshiya

Shinshu University, Japan

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