Synthesis of Fused sp3-Enriched Imidazoles.

A synthetic approach to imidazoles annulated to saturated six-membered cycles featuring S, SO₂, NH, NCbz was developed. It was achieved by combining the Neber rearrangement and the Marckwald reaction. The Neber rearrangement applied to cyclic ketones allowed us to prepare in hundred gram quantities previously unknown α-amino ketones. Unstable tosyl ketoximes were used without purification immediately after their preparation. α-Amino ketones react with potassium thiocyanate and cyanate in almost a quantitative yield affording highly pure imidazol-2-thiones or imidazol-2-ones. Desulfurization of imidazole-2-thiones using Raney nickel led to the formation of previously unknown 2-unsubstituted fused imidazoles in high yields.