Abstract:The synthesis of vitamin K and its analogues has been an important goal since the biochemical roles of the K vitamins were elucidated. This review presents a detailed account of syntheses of natural K vitamins and analogues that contain side chain functionality.
The use of platinum complexes as catalysts for allylic substitution has been studied. A variety of different complexes catalyse the reaction, and several substrates have been tested. In the alkylation of mono(alkyl)-substituted allylic acetates, regioselectivity is highly dependent on ligand choice. By using tricyclohexylphosphine as the ligand, almost complete formation of branched products is observed. The development of a highly enantioselective (ca. 80-90% ee) reaction that makes use of chiral diphenylphosphinooxazoline ligands (abbreviated as (S)-PN) is also described. The enantioselectivity is highly dependent on the ratio of ligand to platinum (when the ratio ligand/Pt is greater than 1:1, the ee drops off dramatically). This is in contrast to palladium and is interpreted in terms of differing coordination chemistry for the two metals ((S)-PN is hemilabile when complexed to platinum) and should be of significance to future systems that utilise heterobidentate ligands. The crystal structures of two isoelectronic platinum and palladium complexes [[(S)-PN]MCl2] are also described.
A versatile, stereoselective synthesis of 5-hydroxypiperidinones with substituents at N1, C3, and C6 has been developed. The sequence involves ring-closing metathesis of a diene amide and epoxidation of the resulting alkene, followed by base-mediated elimination, and finally hydrogenation.
Abstract:The synthesis of vitamin K and its analogues has been an important goal since the biochemical roles of the K vitamins were elucidated. This review presents a detailed account of syntheses of natural K vitamins and analogues that contain side chain functionality.
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