Syntheses of Cyclic Ureas by α-Ureidoalkylation

The cyclocondensation of ureas, thioureas, guanidines, or sulfamides with an aldehyde or ketone and a suitable nucleophilic compound in accordance with the principle of "α-ureidoalkylation" or "vinylogous ureidoalkylation" leads to the formation of saturated or unsaturated mono- and polycyclic heterocycles. The rings may be separated or may be linked in the 1,2- or 1,3-position. Spiro compounds can also be formed. The 5-, 6-, 7-, and 8-membered rings accessible in this way can contain further hetero atoms such as, for example, O, S, N, or P. Synthesis possibilities, properties, substitution reactions, and rearrangement reactions of these heterocycles are described. 1. Definition and Mechanisms of Cyclocondensations according to the Principle of α-Ureidoalkylation and Vinylogous Ureidoalkylation 2. Cyclocondensations by α-Ureidoalkylation of H-Acidic Compounds 2.1. α-Ureidoalkylation of OH-Acidic Compounds 2.2. α-Ureidoalkylation of SH-Acidic Compounds 2.3. α-Ureidoalkylation of Primary Amines 2.4. α-Ureidoalkylation of Ureas, Thioureas, Guanidines, and Sulfamides 2.5. α-Ureidoalkylation of CH-Acidic Compounds 3. Cyclocondensations by α-Ureidoalkylation of Olefins and Other Unsaturated Compounds 4. Cyclocondensations by α-Ureidoalkylation of Nucleophilic Phosphorus Compounds 5. Cyclocondensations by Vinylogous Ureidoalkylation 6. Closing Comments