0000000000445148
AUTHOR
Winfried Münch
Zwitterionic Aza-Claisen Rearrangements Controlled by Pyrrolidine Auxiliaries - Useful Key Steps in Convergent Enantioselective Syntheses
Chiral pyrrolidine substituents served as efficient auxiliaries in diastereoselective zwitterionic ketene aza-Claisen rearrangements. Palladium-catalysed N-allylation starting from optically active proline and prolinol derivatives, as well as from (2S,5S)-2,5-dimethoxymethylpyrrolidine, gave various allylamines bearing trisubstituted olefin moieties. Treatment with complex carboxylic acid fluorides in the presence of trimethylaluminium induced activated ketene addition to the nitrogen and subsequent [3,3] sigmatropic rearrangement to give γ,δ-unsaturated amides with excellent simple diastereoselectivities and up to 11:1 auxiliary-induced diastereomeric ratios. Cleavage of the pyrrolidine am…
Synthesis of 1-Palmitoyl-2-((E)-9- and (E)-10-nitrooleoyl)-sn-glycero-3-phosphatidylcholines
Extensive investigation of nitrated phospholipids in connection with various biologically important processes requires reliable access to suitable material. A selective chemical synthesis introducing a defined nitrofatty acid at the sn-2 position of a 2-lyso sn-glycero-3-phosphatidylcholine was developed. Given that the nitroalkene moiety of both reactant nitrofatty acid derivative and the product esters is characterised by particular sensitivity to nucleophile addition and, depending on the intermediate, subsequent olefin isomerisation and retro-Henry-type reaction, a reliable two-step ester formation was introduced. The activation of the nitrofatty acid succeeded after reaction with trich…
Synthesis and Derivatization of Substituted (R)- and (S)-C-Allylglycines
Various (R)- and (S)-C-allylglycine derivatives were synthesized by means of an auxiliary controlled diastereoselective aza-Claisen rearrangement. Starting from (S)-configured auxiliaries derived from optically active proline, an aza-Claisen rearrangement enabled us to synthesize α(R)-configured γ,δ-unsaturated amides. Since (R)-allylglycine derivatives could be directly generated by reacting N-allylproline derivatives and various protected glycine fluorides, the corresponding (S)-enantiomers were built-up via an initial α-chloroacetyl chloride rearrangement and a subsequent chloride azide substitution with complete inversion of the configuration. High diastereoselectivities were obtained (…