M. Silveira, Erin E. Templet, F. Fronczek
Apr 1, 2011
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Journal
Journal of Chemical Crystallography
Abstract
This paper reports a synthesis of 9-bromo, 2-fluoro substituted, and Z-ring locked (by a trimethylene bridge at C8 and C11) crystalline fluorine substituted bicyclic ring-fused polyene bearing a δ-bromo-α,β,γ,δ-unsaturated ester unit. It is a structural element found in sterically hindered retinoids and is a useful advanced intermediate in the total synthesis of these naturally occurring bioactive polyenes. The synthon, 8-fluoro-1-benzosuberone was converted into 9-bromo-2-fluoro-6,7-dihydro-5H-benzocycloheptene-8-carboxaldehyde chemoselectively and regioselectively and then into 9-bromo-2-fluoro-8-[ethyl, (E)-2-propenoate-3-yl]-6,7-dihydro-5H-benzocycloheptene in a step economical and stereoselective manner by treatment with triethylphosphonoacetate and NaH in THF. The process creates a new carbon–carbon double bond between C12 and C13 and produces a previously unreported product that has been characterized by X-ray, IR, 1H NMR, 13C NMR, GC–MS, and elemental analysis. Crystals are triclinic, space group P-1, a = 7.581(2), b = 8.324(2), c = 11.759(3) Å, α = 96.723(17), β = 96.056(16), γ = 101.999(17)°, Z = 2.Graphical AbstractThe synthesis and characterization of the previously unreported δ-bromo-α,β,γ,δ-unsaturated ester derivative is reported. Crystals are triclinic, space group P-1, a = 7.581(2), b = 8.324(2), c = 11.759(3) Å, α = 96.723(17), β = 96.056(16), γ = 101.999(17)°, Z = 2.