Highly Diastereoselective NHC-Catalyzed [4+3] Annulation of Enals, Aldehydes and N-Phenyl Urea/Thiourea for the Synthesis of Monocyclic trans-1,3-Diazepanes
摘要:
N-Heterocyclic carbene catalyzed synthesis of 1,3-diazepanes from ,-unsaturated aldehydes, N-phenyl urea/thiourea and aromatic aldehydes has been developed. The reactive Breslow intermediate, formed by reaction of the enal with the NHC, attacks as a d(3) nucleophile at the 1-arylidene-3-arylurea derivative, which is produced by simple reaction of N-phenyl urea/thiourea with an aromatic aldehyde. The resulting intermediate, on subsequent heterocyclization, forms the product with high yield. The reaction proceeded smoothly with high atom economy, producing a new C-C and a new C-N bond in a one-pot operation.