4-Selenophosphoryl-1,2-disubstituted imidazoles have been obtained by thermal decomposition of methyl 5-(diamidoselenophosphoryl)-imidazolium chlorides. The position of selenophosphoryl group in the imidazole ring was proved by H-1, C-13 NMR spectroscopy, and X-ray analysis. Previously unknown diamido- and dichloro(imidazol-4-yl)-phosphonites were synthesized, and differences in their reactivity compared to analogous 5-phosphorylated imidazoles are shown. (C) 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:103-118, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20584