Regioselective Activation of Benzocyclobutenones and Dienamides Lead to anti-Bredt Bridged-Ring Systems by a [4+4] Cycloaddition
Tao Xu reports on the creation of anti-Bredt bridged-ring systems by a [4+4] cycloaddition.
Bridged-ring systems are common structural motifs in many functional molecules, including bioactive natural compounds. The anti-Bredt rule has been used to qualitatively define bridged-ring systems with olefins at bridgehead position. Professor Tao Xu from the Ocean University of China (Qingdao, P. R. of China) mentioned that bridged skeletons are characterized by their size and ring strain. He further explained: “While the sp2-hybridized BC underpins certain limitations on both the ring size (m+n≥7) as well as ring strain, examples can still be found in a number of natural products. However, benzo-fused BC-bearing [m.n.1] systems are unusual (m+n>8) and, to the best of our knowledge, unknown to chemists when confined in a small ring (m+n≤8) framework.”
The research group of Professor Xu wanted to address this challenge and try to expand the anti-Bredt rule.