title: AlCl₃-Catalyzed Ring Expansion Cascades of Bicyclic Cyclobutenamides Involving Highly Strained Cis,Trans-Cycloheptadienone Intermediates.
abstract: We report the first experimental evidence for the generation of highly strained cis,trans-cycloheptadienones by electrocyclic ring opening of 4,5-fused cyclobutenamides. In the presence of AlCl3, the cyclobutenamides rearrange to [2.2.1]-bicyclic ketones; DFT calculations provide evidence for a mechanism involving torquoselective 4π-electrocyclic ring opening to a cis,trans-cycloheptadienone followed by a Nazarov-like recyclization and a 1,2-alkyl shift. Similarly, 4,6-fused cyclobutenamides undergo AlCl3-catalyzed rearrangements to [3.2.1]-bicyclic ketones through cis,trans-cyclooctadienone intermediates. The products can be further elaborated via facile cascade reactions to give complex tri- and tetracyclic molecules.
authors.affiliation: †School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou, Henan 450001 P. R. China.|‡Division of Pharmaceutical Sciences and Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53705 United States.
authors.forename: Xiao-Na
authors.initials: XN
authors.lastname: Wang
authors.affiliation: §School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Krenske
authors.affiliation: §School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Ryne C
authors.initials: RC
authors.lastname: Johnston
authors.affiliation: ∥Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095 United States.
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
authors.affiliation: ‡Division of Pharmaceutical Sciences and Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53705 United States.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Hsung
mesh_terms: D000077410:Aluminum Chloride; D017607:Aluminum Compounds / Q000737:chemistry*; D000577:Amides / Q000138:chemical synthesis / Q000737:chemistry*; D001643:Bridged Bicyclo Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D002384:Catalysis; D002712:Chlorides / Q000737:chemistry*; D003500:Cyclization; D003503:Cyclobutanes / Q000138:chemical synthesis / Q000737:chemistry*; D007659:Ketones / Q000138:chemical synthesis / Q000737:chemistry; D008958:Models, Molecular; D013237:Stereoisomerism
chemical_list: D017607:Aluminum Compounds; D000577:Amides; D001643:Bridged Bicyclo Compounds; D002712:Chlorides; D003503:Cyclobutanes; D007659:Ketones; D000077410:Aluminum Chloride