Effect of Substitution on the Intramolecular 1,3-Dipolar Cycloaddition of Alkene Tethered Muenchnones

摘要

A sequence of chembselective activation of N-acylaminoacids, muenchnone generation, intramolecular 1,3-dipolar cycloaddition, and ring opening efficiently generated functionalized polycyclic structures such as cyclopenta[b]pyrroles or zwitterionic bicyclo[4.3.0]nonane or bicyclo[3.3.0]octanes in one operation is given. These zwitterionic species were isolated for the first time and were subsequently reduced to bicyclic aminoalcohols. The effect of the substitution of both the dipolarophile and the muenchnone on the intramolecular cycloaddition outcome was examined. It was found that either nonactivated or electron-poor alkenes can react with the muenchnone if these alkenes are tethered at position 4 on the muenchnone (2, R~2 = alkene tether), whereas only an electron-poor alkene at position 2 (2, R~3 = alkene tether) could undergo successful cycloaddition. Also, muenchnones substituted at position 2 with a phenyl (2, R~3 = Ph) showed a dramatic increase in reactivity, whereas a phenyl at position 4 (2, R~2 = Ph) had a very limited effect.