Aromatics to Triquinanes. Synthesis and Photoreaction of Tricyclo[5.2.2.02,6]undecanes Having an α-Methoxy β,γ-Unsaturated Carbonyl Chromophore: A Novel, Efficient, and General Route to Linearly Fused Cis:Anti:Cis Tricyclopentanoids

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-methoxyspiro[cyclohexa-2,4-diene-6-2‘-oxacyclopropan]one with various dienophiles and the photochemical reaction of appropriately designed tricyclic systems, having an α-methoxy β,γ-enone chromophore upon triplet ( 3 T) 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 α-methoxy β,γ-enone chromophore ( 23 − 36 ) from o -vanillyl alcohol has been reported. The 2-methoxyspiro[cyclohexa-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) 1 H NMR, 13 C 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 α,β-enone chromophore, gave a highly unusual pentacyclic product 55 as a result of participation of the OCH 3 group in the photoreaction.