Synthesis and Catalytic Activity of Spaced Ferrocene Oxazolines

Abstract

Chiral 2-[{N-aryl-N-(ferrocenylmethyl)amino}methyl]-4-(1-methylethyl)-4,5-dihydroxazoles with various substituents at the aryl ring were prepared by alkylation of N-(ferrocenylmethyl)anilines, FcCH2NHC6H4R (Fc = ferrocenyl), with (S)-2-(chloromethyl)-4-(1-methylethyl)-4,5-dihydrooxazole. The oxazoles, substituted anilines, and the precursors of the latter, the respective Schiff bases FcCH=NC6H4R, were characterized by standard methods and further studied by mass spectrometry. The oxazoles were further tested as chiral auxiliaries in the addition of diethylzinc to benzaldehyde but showed only negligible asymmetric induction (ee ca 10%), most likely due to steric hindrance of the nitrogen donor centres. This steric restriction seems to be lowered upon replacement of the substituted phenyl group with a benzyl substituent; compounds FcCH2NHCH2Ph and (R)-FcCH2NHCH(Me)Ph are easily alkylated yielding [FcCH2NMe2(CH2Ph)]I (9) and 2-[{N-(1-phenylethyl)-N-(ferrocenylmethyl)amino}methyl]-4-(1-methylethyl)-4,5-dihydroxazole (10), respectively. Solid-state structures of FcCH2NHC6H4R (R = 2-Me and 4-Cl), 9, and 10 have been determined by single-crystal X-ray diffraction.