Stereochemistry of Substitution of the α-Dimethylamino Group by Dialkylzinc in Chiral Benzylferrocene

Abstract

The stereochemistry of the substitution of the α-dimethylamino group by dimethylzinc in the presence of acetyl chloride in the chiral benzylferrocene backbone was examined. The reaction with the benzylferrocene bearing an o-bromo substituent at both ferrocene and the phenyl ring proceeded with inversion of configuration, while the reaction with the benzylferrocene bearing an o-bromo substituent at either ferrocene or the phenyl ring proceeded with retention of configuration.

Selective Syntheses of Planar-Chiral Ferrocenes

“…The reversion of configuration of the chiral plane is due to Fe–Li interactions as well as a dimeric arrangement of the organolithium fragments, which is supported by DFT calculations . Regarding the nucleophilic substitution reaction, it has been found that for benzylferrocenes such as 96 and 97 , depending on the configuration of the α-carbon atom and the chiral plane as well as the presence of an ortho substituent at the ferrocene and/or the benzene moiety the displacement of the NMe 2 group proceeds with either full retention or full inversion of configuration rather than partial epimerization. , …”

“…119 Regarding the nucleophilic substitution reaction, it has been found that for benzylferrocenes such as 96 and 97, depending on the configuration of the α-carbon atom and the chiral plane as well as the presence of an ortho substituent at the ferrocene and/or the benzene moiety the displacement of the NMe 2 group proceeds with either full retention or full inversion of configuration rather than partial epimerization. 96,120 If the NMe 2 functionality in (R)-77 is replaced by OMe, directed metalation proceeds much less regio-and stereoselectively, leading to a mixture of 1,2-, 1,3-, and 1,1′-disubstituted ferrocenes in ratios depending on the solvent and reaction time, as shown by Ugi and co-workers. 121 The asymmetric induction was estimated to be only about 10% of that of the corresponding amine.…”

“…This includes utilization of N,N-dimethyl-1-ferrocenylalkylamines and -benzylamines (85), 77,80−96 homoannularly bridged N,N-α-dimethylamino-1,2-tetramethylene ferrocenes (86), 97−101 heteroannularly bridged [3] (87, 100,102−105 88 106,107 )-and [5]ferrocenophanes (89) 108,109 as well as bisferrocenyldiamines ( 90) 110 (Chart 2). The enantiopure starting materials 85−90 have been made available among others by resolution, 97,102,106 asymmetric reductions of ferrocenyl ketones 77,80,82,94,96,108,111,112 and imines, 105,113 asymmetric alkylation/arylation of ferrocenealdehydes, 114,115 and the use of enantiomerically pure cyclopentadienes or cyclopentadienyl ligands. 88,99,116,117 It should be noted that ferrocenophanes 87−89 exhibit a reversed selectivity toward ortho-directed lithiation in comparison to Ugi's amine.…”

“…In the last few decades it has been found that Ugi’s approach is applicable to related substrates, revealing almost the same stereoselectivities regarding ortho-directed lithiation and nucleophilic substitution of the amine moiety. This includes utilization of N , N -dimethyl-1-ferrocenylalkylamines and -benzylamines ( 85 ), ,− homoannularly bridged N , N -α-dimethylamino-1,2-tetramethylene ferrocenes ( 86 ), − heteroannularly bridged [3] ( 87 , ,− 88 , )- and [5]ferrocenophanes ( 89 ) , as well as bisferrocenyldiamines ( 90 ) (Chart ). The enantiopure starting materials 85 – 90 have been made available among others by resolution, ,, asymmetric reductions of ferrocenyl ketones ,,,,,,, and imines, , asymmetric alkylation/arylation of ferrocenealdehydes, , and the use of enantiomerically pure cyclopentadienes or cyclopentadienyl ligands. ,,, …”

Packing Principles for Donor–Acceptor Oligomers from Analysis of Single Crystals

“…Long-axis (up) and lateral projections (down) of the crystal lattices of Th/Ph co-oligomers, which have −Th– units of odd number: (a) 2,5-bis­(4′-methoxybiphenyl-4-yl)­thiophene, (b) 5,5″-di­(biphenyl-4-yl)-terthiophene, and (c) 4′,4‴-(thiophene-2,5-diyl)­bis­([1,1′-biphenyl]-4-carbonitrile) …”