Aromatics to Triquinanes. Synthesis and Photoreaction of Tricyclo[5.2.2.0<sup>2,6</sup>]undecanes Having an α-Methoxy β,γ-Unsaturated Carbonyl Chromophore: A Novel, Efficient, and General Route to Linearly Fused <i>Cis</i>:<i>Anti</i>:<i>Cis</i> Tricyclopentanoids
作者:Vishwakarma Singh、Beena Thomas
DOI:10.1021/jo9702296
日期:1997.8.1
A novel, general, and stereoselective route for rapid creation of functionalized, linearly fused cis:anti:cis triquinanes from aromatic precursors has been presented. Cycloaddition of 2-methoxy-spiro[cyclohexa-2,4-diene-6-2'oxacyclopropan]one with various dienophiles and the photochemical reaction of appropriately designed tricyclic systems, having an alpha-methoxy beta,gamma-enone chromophore upon triplet (T-3) sensitization, are the key elements of our approach. A new and efficient methodology for the synthesis of endo-annulated bicyclo[2.2.2]octenones having an alpha-methoxy beta,gamma-enone chromophore (23-36) from o-vanillyl alcohol has been reported. The 2-methoxyspiro[cyclo-hexa-2,4-diene-6-2'-oxacyclopropan]one was generated by oxidation of o-vanillyl alcohol and trapped with cyclopentadiene (17), spiroheptadiene (18), and dimethylfulvene (19) to give the adducts 20-22 which were elaborated to a variety of chromophoric systems 23-36. The structure and stereochemistry of the tricyclic chromophoric systems (20-36) has been established through their high-field (300 MHz) H-1 NMR, C-13 NMR, and COSY spectra. Triplet-sensitized photochemical reaction of the chromophoric systems (23, 28-35) has been investigated. The triplet excitation of 28-34 led directly to the formation of functionalized triquinanes (43-48) in a single, stereoselective step. Interestingly, the irradiation of 23 furnished a novel tetracyclic product 40, whereas the irradiation of the substrate 35, having an additional alpha,beta-enone chromophore, gave a highly unusual pentacyclic product 55 as a result of participation of the OCH3 group in the photoreaction.