3-Methyl-4,5-di-hydro-oxazolium tetra-phenyl-borate.

In the cation of the title salt, C4H8NO(+)·C24H20B(-), the C-N bond lengths are 1.272 (2), 1.4557 (19) and 1.4638 (19) Å, indicating double- and single-bond character, respectively. The C-O bond length of 1.3098 (19) Å shows that double-bond character and charge delocalization occurs within the NCO plane of the cation. In the crystal, a C-H⋯π inter-action is present between the methyl-ene H atom of the cation and one phenyl ring of the tetra-phenyl-borate ion. The latter forms an aromatic pocket in which the cation is embedded.