New chiral ferrocenyl P,S-ligands for highly diastereo- and enantioselective Ag(I)-catalyzed asymmetric [3+2] cycloaddition of azomethine ylides

A new family of chiral ferrocenyl P,S-ligands incorporating an indole ring at the α-ferrocenylmethyl position has been prepared via a Friedel–Crafts alkylation reaction of (Rc,SFc)-PPFA with a variety of 2-indole thioethers. These newly developed ferrocenyl P,S-ligands proved to be efficient in the AgOAc-catalyzed asymmetric [3+2] cycloaddition of azomethine ylides with various dipolarophiles, giving cycloadducts with high diastereoselectivities and enantioselectivities (up to 99% ee).

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3-{(S)-1-[(S)-2-(Diphenylphosphino)ferrocenyl]ethyl}-2-(phenylthio)indoleC38H32FeNPSee >98%[α]D20=-100.7 (c 0.12, CHCl3)Source of chirality: (Rc,SFc)-PPFAAbsolute configuration: (Sc,SFc)

3-{(S)-1-[(S)-2-(Diphenylphosphino)ferrocenyl]ethyl}-2-[(4-methylphenyl)thio]indoleC39H34FeNPSee >98%[α]D20=-86.8 (c 0.11, CHCl3)Source of chirality: (Rc,SFc)-PPFAAbsolute configuration: (Sc,SFc)

3-{(S)-1-[(S)-2-(Diphenylphosphino)ferrocenyl]ethyl}-2-[(4-chlorophenyl)thio]indoleC38H31ClFeNPSee >98%[α]D20=-67.4 (c 0.15, CHCl3)Source of chirality: (Rc,SFc)-PPFAAbsolute configuration: (Sc,SFc)

3-{(S)-1-[(S)-2-(Diphenylphosphino)ferrocenyl]ethyl}-2-(benzylthio)indoleC39H34FeNPSee >98%[α]D20=-239.6 (c 0.12, CHCl3)Source of chirality: (Rc,SFc)-PPFAAbsolute configuration: (Sc,SFc)

3-{(S)-1-[(S)-2-(Diphenylphosphino)ferrocenyl]ethyl}-2-(methylthio)indoleC33H30FeNPSee >98%[α]D20=-215.0 (c 0.13, CHCl3)Source of chirality: (Rc,SFc)-PPFAAbsolute configuration: (Sc,SFc)

3-{(S)-1-[(S)-2-(Diphenylphosphino)ferrocenyl]ethyl}-2-(i-propylthio)indoleC35H34FeNPSee >98%[α]D20=-248.4 (c 0.12, CHCl3)Source of chirality: (Rc,SFc)-PPFAAbsolute configuration: (Sc,SFc)

N-tert-Butyloxycarbonyl-3-{(S)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}-2-(phenylthio)indoleC43H40FeNO2PSee >98%[α]D20=-96.9 (c 0.12, CHCl3)Source of chirality: (Rc,SFc)-PPFAAbsolute configuration: (Sc,SFc)