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Solid-phase Synthesis of [4.4] Spirocyclic Oximes
Published on: February 6, 2019
A highly stereoselective synthesis of 11Z-retinal using tricarbonyliron complex
Abstract:
A stereoselective synthesis of 11Z-retinal 2, which is the chromophore of visual pigment (rhodopsin), was accomplished from the beta-ionylideneacetaldehyde-tricarbonyliron complex 3. The Peterson reaction of 3 using ethyl trimethylsilylacetate smoothly proceeded to afford predominantly the Z-ester 6. Transformation of the Z-ester 6 to the methyl ketone 19, followed by the Emmons-Horner reaction of 19 with C2-cyanophosphonate, produced ethyl 11Z, 13E-retinonitrile-tricarbonyliron complex 21 as the only product. Decomplexation of 21 with CuCl2 and subsequent DIBAL reduction gave 11Z-retinal 2 in excellent yield. Mechanistic consideration of Z-selectivity in the Peterson reaction of the aldehyde-tricarbonyliron complex is also discussed.
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