With the intent of exploring the potential of a new class of a chiral bicyclic oxazolidine fused N-heterocyclic carbenes namely, {(3S)-3-R-7-phenyl-2,3-dihydroimidazo[5,1-b]oxazol-5-ylidene }(R= sec-butyl, i-butyl, i-propyl), in homogeneous catalysis, its rhodium and iridium complexes have been tested as precatalysts for asymmetric transfer hydrogenation of ketones. In particular, the N-heterocyclic carbene precursors, {(3S)-3-R-6-methyl-7-phenyl-2,3-dihydroimidazo[5,1-b]oxazol-6-ium iodide (R= sec-butyl (1f), i-butyl (2f), i-propyl (3f)}, were obtained in enantiopure form using a multi-step sequence starting from commercially available available amino acids avoiding any tedious chiral resolution step. The rhodium(I) (1-3)h and the iridium(I) (1-3)i complexes were obtained by transmetallation method from its silver complexes (1-3)g, which in turn was prepared from (1-3)f by threatment with Ag2O. Both of the rhodium(I) (1-3)h and the iridium(I) (1-3)i complexes effectively catalyzed the asymmetric transfer hydrogenation of ketones exhibiting an enantiomeric excess of up to 26 %.

Asymmetric transfer hydrogenation of ketones by rhodium and iridium complexes of chiral oxazolidine fused N-heterocyclic carbene ligands

253rd National Meeting (2017)

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