(−)‐Sparteine‐Mediated Directed ortho‐Metalation of N‐Cumyl‐N‐ethylferrocenecarboxamide. Versatile Routes to Functionalized Planar Chiral Ferrocenecarboxamides, Amines, Esters and Phosphines

Abstract

N-Cumyl-N-ethylferrocenecarboxamide 5 provides planar chiral carboxamides 6 in high yield and % ee via (À)-sparteine-mediated directed orthometalation. Mild decumylation affords secondary amides 7, which serve as intermediates for a convenient and general route to the venerable Ugi planar chiral ferrocenylamines 13 and as versatile precursors for the preparation of novel chiral ferrocenes 15 and 20. The chiral TMS-ferrocenyl derivative 7c is used to prepare the enantiomeric (S)-7f, circumventing the lack of availability of ()-sparteine.

The First Anionic Thia‐Fries Rearrangements at Ferrocene: Ready Access to Trifluoromethylsulfonyl‐Substituted Hydroxyferrocenes and an Extremely High Interannular Stereoinduction between Cyclopentadienyl Ligands

“…[31][32][33][34] When 1,1'-ferrocenediyl ditriflate (9), was treated with 2.2 equivalents of LDA at À78 8C, instead of a single or double triflate elimination, another double anionic thia-Fries rearrangement was observed in 85% yield, which could in principle afford two diastereomeric rearrangement products 16 and 17. Remarkably, the reaction takes place with full diastereoselectivity affording only one of the two diastereomers.…”

Structure Formation Principles and Reactivity of Organolithium Compounds

“…Coming from tetrameric (tBuLi) 4 this process is generally assumed to take place through cleavage of the tetramer into two dimeric species. In a thought experiment, [(tBuLi) 3 ·C 6 H 15 N 3 ] leads us to suggest the formation of a monomeric species through the coordination of three of the four tBuLi molecules by a tridentate ligand, such as by the cyclic triazacyclohexane ( Figure 11). The remaining tBuLi can than be stabilised as a monomeric adduct by a further ligand, such as (À)-sparteine or (R,R)-TMCDA.…”

“…Hereby, the axial hydrogen atoms of the cyclohexane ring prevent the formation of an aggregate such as [(iPrLi) 3 ·A C H T U N G T R E N N U N G (TEEDA) 2 ] or a dimeric structure. [28] iPrLi·A C H T U N G T R E N N U N G (R,R)-TECDA is the only monomeric isopropyllithium and shows shortened bond lengths typical for monomeric alkyllithium compounds.…”

“…Hereby, the ethyl groups of the nitrogen ligand prevent the formation of a dimeric compound; instead a dimer is formed, in which a monomeric isopropyllithium unit is inserted (Figure 9). [28] [(iPrLi) 3 ·A C H T U N G T R E N N U N G (TEEDA) 2 ] consists of three iPrLi and two TEEDA molecules. Whereas, Li1 and Li2 show LiÀC and LiÀN distances in the range of dimeric organolithium compounds, Li3 possesses shortened distances typical for monomers.…”

“…[2] In recent years, developments in the ligand design have lead to many applications and new types of reactions, such as asymmetric deprotonation or addition reactions. [3] Structure elucidation, kinetic measurements and theoretical studies have contributed to an improved understanding of the on-going processes. However, the clarification of most of the reaction mechanisms is still a great challenge and the development of further applications of the organolithium adducts remains a major endeavour in synthetic chemistry.…”