Chiral ferrocenyl ligands with bidentate pyridine donors. Synthesis and application in Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenylpropenyl-1-esters

A synthetic procedure relying on the Friedländer condensation of enantiopure α-amino ferrocenecarboxaldeyde has been devised for the regio-designed elaboration of a pyridine nucleus fused onto the ferrocene scaffold. Three novel bidentate ligands with different pyridine nitrogen donors featuring the [3,2-b]ferrocenopyridine fragment a as the sole chirogenic element have been prepared in enantiopure form through a multi step route involving the diastereoselective deprotonation of a chiral acetal of ferrocenecarboxaldehyde in the stereodetermining step. The ligands were assessed in the Pd-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl esters with good stereoselectivity.

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6-(2′-Pyridyl)ferroceno[3,2-b]pyridineC18H14FeN2Ee >99%Configuration (S)Source of chirality (S)-1,2,4-butanetriol

5,6-Dihydro-ferroceno[3,2-b]1,10-phenantrolineC24H24FeN2Ee >99%Configuration (S)Source of chirality (S)-1,2,4-butanetriol

6-(2′-Quinolyl)ferroceno[3,2-b]pyridineC22H21FeN2Ee >99%Configuration (S)Source of chirality (S)-1,2,4-butanetriol