Brønsted‐Acid Catalyzed Aldehyde Insertion to Construct C−X Bond: High Regio‐ and Chemoselectivity Synthesis of Dihydrobenzo[1,5]oxazocines and Pyrrolo[3,4‐ d]tetrahydropyrimidines

Abstract

Aldehydes as one of the most widely building blocks, have been frequently utilized as privileged C1 electrophile units and exhibited versatile applications to construct carbon‐heteroatom and carbon‐carbon bond. We herein described a novel Brønsted‐acid catalyzed aldehydes insertion reaction with maleimide‐based 1, n‐C, O/N‐synthons, involving a high regio‐ and chemoselectivity [6/7 + 1]or [3 + 1 + 1 + 1]manner. The maleimide‐based 1, n‐C, O/N‐synthons (n = 3, 6, 7) were originally designed and developed by our group which were used as flexible bisnucleophiles. By this tandem annulations approach, two types of structurally diverse medium‐sized heterocycles were synthesized in good to excellent yields (74–91 %) and with excellent selectivity, including dihydrobenzo[1,5]oxazocines (24 examples) and pyrrolo[3,4‐ d]tetrahydropyrimidines (22 examples). Significantly, formaldehyde, long‐chain aliphatic aldehydes and aromatic aldehydes can act as C1 electrophile units catalyzed by racemic BINOL‐derived phosphoric acid catalyst in these transformations, which then selectively attacked the OH or NH group bearing in functionalized maleimides and underwent the formation of C−C, C−O or C−N bond in a short time under microwave irradiation conditions.