Competitive stereochemical control operative during conrotatory electrocyclization of helically equilibrating diquinanyl-substituted 1,3,5,7-octatetraenyl bisenolates.
[Carbohydrate structure: see text] 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.
Paquette
Leo A
LA
Evans Chemical Laboratories, Ohio State University, Columbus, Ohio 43210, USA. paquette.1@osu.edu
Liu
Zuosheng
Z
Ramsey
Charla
C
Gallucci
Judith C
JC
D000475:Alkenes; D000838:Anions; D004563:Electrochemistry / Q000379:methods; D004987:Ethers / Q000138:chemical synthesis; D006844:Hydrocarbons, Cyclic / Q000138:chemical synthesis*; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013237:Stereoisomerism
D000475:Alkenes; D000838:Anions; D004987:Ethers; D006844:Hydrocarbons, Cyclic; D007202:Indicators and Reagents