88206-73-9Relevant academic research and scientific papers
Total syntheses of (-)-grandinolide and (-)-sapranthin by the sharpless asymmetric dihydroxylation of methyl trans-3-pentenoate: Elucidation of the stereostructure of (-)-sapranthin
Harcken, Christian,Brueckner, Reinhard,Rank, Elisabeth
, p. 2342 - 2352 (1998)
Methyl trans-3-pentenoate (7) was converted into the cis-substituted γ- lactone 8 in a single step with 78% ee. The derived enolate dilithio-8 was alkylated trans-selectively with primary iodoalkanes with 1-iodobutane dilithio-8 afforded, after esterification with isovaleroyl chloride, the epi- blastmycinone 9. Dilithio-8 gave (-)-grandinolide (II) with 1-iodo-19- phenylnonadecane (20). A third trans-selective alkylation of dilithio-8 was undertaken with 16-iodo-1,5-hexadecadiene-7,9-diyne (21). This gave the γ- 1actone 12, which had the published relative configuration of (-)-sapranthin but different spectroscopic data. When the OH group of lactone 8 was inverted (to hydroxylactone 40) and the derived enolate dilithio-40 alkylated with iodide 21, lactone 41 resulted. Its 1H and 13C NMR spectra and the sign and value of optical rotation coincide with the data of natural sapranthin. These findings establish that (-)-sapranthin possesses the relative and absolute configuration of stereoformula 41. The synthesis of iodide 21 was performed via the dienoic carboxylic ester trans-23 which stemmed from the Claisen-Ireland rearrangement (27 → 28/29)/esterification (28/29 → 26)/Cope rearrangement (26 → 23) sequence shown in Scheme 5.
