Ferrocenyloxazoline-Derived Planar Chiral Palladacycles: C–H Activation, Transmetalation, and Reversal of Diastereoselectivity

Ross A. Arthurs, David L. Hughes, Christopher J. Richards

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Abstract

Reinvestigation of the palladation of (S)-2-ferrocenyl-4-(methylethyl)oxazoline with Pd(OAc)2 in CH2Cl2 was found to proceed with a dr of 3.6:1 in favor of the resulting S,Sp palladacycle. A similar 4:1 dr was obtained using Na2PdCl4 in MeOH. As an alternative approach, highly diastereoselective lithiation (dr >100:1) and transmetalation were investigated. Addition of PdX2(COD) (X = Cl, Br) to (S,Rp)-2-lithio-1-(2′-(4′-methylethyl)oxazolinyl)ferrocene resulted in double halide substitution and formation of cis-(S,S,Sp,Sp)-bis[2-(2′-(4′-methylethyl)oxazolinyl)ferrocene-1-C,3′-N]palladium(II) (42% from X = Cl, 50% from X = Br). Selective monoprotodepalladation with HCl gave an S,Sp palladacycle containing a removable ferrocenyloxazoline ligand. Addition of PdCl2(MeCN)2 to mercuracycles in acetonitrile, themselves generated from Li–Hg transmetalation, followed by a brine wash gave (S,Sp)-di-μ-chlorobis[2-(2′-(4′-methylethyl)oxazolinyl)ferrocene-1-C,3′-N]dipalladium(II) as a single diastereoisomer in high yield. The alternative S,Rp diastereoisomer was obtained in the same way by use of a deuterium blocking group to reverse lithiation diastereoselectivity.
Original languageEnglish
Pages (from-to)4271-4279
JournalOrganometallics
Volume38
Issue number21
Early online date24 Oct 2019
DOIs
Publication statusPublished - 11 Nov 2019

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