imines of sydnones (i.e. having an imino group in place of the exocyclic oxygen atom).
S06206.png
(These structures represent only two canonical forms.)
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1371 (https://doi.org/10.1351/pac199567081307)