Enantioselective Twofold C−H Annulation of Formamides and Alkynes without Built‐in Chelating Groups

Abstract

Twofold CÀH annulation of readily available formamides and alkynes without built-in chelating groups was achieved. NiÀAl bimetallic catalysis enabled by a bulky BINOL-derived chiral secondary phosphine oxide (SPO) ligand proved to be critical for high reactivity and high selectivity. This reaction uses readily available formamides as starting materials and provides a concise synthetic pathway to a broad range of chiral ferrocenes in 40-98 % yield and 93-99 % ee.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.Scheme 4. Scope with respect to the formamides. Reaction conditions: 1 (0.2 mmol), 2 a (0.5 mmol), toluene (1.0 mL) under N 2 for 10 min to 2 h. Yields of isolated product are given. [a] 120 8C. MOM = methoxymethyl, SEM = trimethylsilylethoxymethyl. Angewandte Chemie Communications Angewandte Chemie Communications 9431

Enantioselective C–H Alkenylation of Ferrocenes with Alkynes by Half-Sandwich Scandium Catalyst

“…Ferrocene and its derivatives have been the subject of extensive studies since the discovery of ferrocene in the early 1950s, because of their fascinating structural features and properties. − In particular, ferrocenes possessing planar chirality are of great interest and importance in the fields of asymmetric catalysis and materials science. Therefore, the development of efficient protocols to introduce planar chirality into the ferrocene backbone has attracted intense attention over the past decades. − In view of the high potential of chiral hybrid olefin ligands containing both a heteroatom and an olefin unit in asymmetric catalysis, − planar-chiral ferrocenes bearing both N -heterocycle and alkene functionalities are of great interest. In principle, the asymmetric C–H addition of N -heterocycle-substituted ferrocenes to alkynes could be a straightforward and 100% atom-efficient route for the synthesis of planar-chiral ferrocenes bearing N /alkene functionalities .…”

Iodoferrocene as a partner inN-arylation of amides

“…While successful reactions have been documented in the benzene series, 42 there is to the best of our knowledge no corresponding reactions reported in the ferrocene series. However, examples in which N-substituted formamides are coupled with iodoferrocenes are reported under similar conditions, 43 explaining why single N-arylation is difficult in this case.…”

Bimetallic anchoring catalysis for C-H and C-C activation

“…Following this racemic reaction, Ye's group [41] then designed a BINOL-derived chiral PO ligand (PO 6 ) and developed an enantioselective twofold C-H annulation of ferrocene-based formamides and alkynes. Various diaryl alkynes and dialkyl alkynes were well tolerated, providing a series of chiral ferrocenes in 40%−98% yield and 93%−99% ee (Scheme 32).…”