Rearrangements of N-acyl isothioureas. Alternate access to acylguanidines from cyanamides.

We report a tin-free one-pot radical approach to the synthesis of N-acyl isothioureas and acylguanidines from N-acyl cyanamides. Photoactivated reduction of aromatic disulfides in the presence of Hünig's base results in hydrothiolation of the cyanamide moiety, followed by spontaneous 1,3-migration of the acyl group. Onward reaction of the isothioureas obtained with amines led to the corresponding N-acylguanidines, where the acyl group is attached to the nitrogen atom formerly at the cyano-end of the starting material.