1380511-97-6Relevant articles and documents
Zwitterionic aza-Claisen rearrangements controlled by pyrrolidine auxiliaries-useful key steps in convergent enantioselective syntheses
Friedemann, Nora M.,Haerter, Alice,Brandes, Sebastian,Gross, Steffen,Gerlach, Dorothea,Muench, Winfried,Schollmeyer, Dieter,Nubbemeyer, Udo
supporting information; experimental part, p. 2346 - 2358 (2012/05/20)
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 amide was achieved through iodolactonization, with the option for recovery of the auxiliary pyrrolidine. The stereochemical outcomes of the rearrangements and the iodocyclizations were established by X-ray and NOEDS analyses of suitable amides and lactones. Overall, both enantiomers were accessible selectively. The optically active amides and lactones of defined configurations formed in this way should be useful as key intermediates in convergent steroidal natural and pharmaceutically important product synthesis. Enantiopure N-allylpyrrolidines and 4-arylbut-3-enoyl fluorides underwent zwitterionic aza-Claisen rearrangements in high yields, as well as with high simple and up to 11:1 auxiliary-induced diastereoselectivities. After selective olefin hydrogenation, iodocyclization and pyrrolidine removal enabled synthesis of the lactones. Both enantiomers of target molecules could be achieved selectively.
