Competitive Stereochemical Control Operative during Conrotatory Electrocyclization of Helically Equilibrating Diquinanyl-Substituted 1,3,5,7-Octatetraenyl Bisenolates

• Published in: Journal of organic chemistry Vol. 70; no. 20; pp. 8154 - 8161
• Main Authors: Paquette, Leo A, Liu, Zuosheng, Ramsey, Charla, Gallucci, Judith C
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 30.09.2005; Amer Chemical Soc
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Alkenes; Anions; Chemistry; Chemistry, Organic; Electrochemistry - methods; Ethers - chemical synthesis; Exact sciences and technology; Hydrocarbons, Cyclic - chemical synthesis; Indicators and Reagents; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Structure; Organic chemistry; Oxidation-Reduction; Physical Sciences; Preparations and properties; Science & Technology; Stereoisomerism; HYPNOPHILIN; SQUARATE ESTER CASCADE; ENOL ETHERS; QUINONES; CONSTRUCTION; NETWORKS; LEAVING GROUP; CYCLOPENTANOIDS; OCTATETRAENE INTERMEDIATE; CYCLOPENTENONES; Lithium Organic compounds; Cyclization; Molecular structure; Electrochemistry; Reaction mechanism; NMR spectrometry; Tetracyclic compound; Stereochemistry; X ray diffraction
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo0513919

Activation of the squarate ester cascade by adding the lithiated bicyclo[3.3.0]octene 20 and vinyllithium sequentially to 1 results in the isolation of the four tetracyclic products 21 − 24. The structures of the topographically complex products were deduced by 2D NMR spectroscopy and X-ray diffraction studies. The mechanistic insights gained by these findings are discussed. The product distribution is telltale evidence for predominant 1,2-addition of the second alkenyl anion. Product stereochemistry is in turn diagnostic of the preferred mode of conrotatory ring closure operating within equilibrating helical intermediates of opposite pitch. A competing pathway for the elimination of methanol in these highly functionalized intermediates has been observed for the first time.