Uwe Schneider

The University of Edinburgh, EaStCHEM School of Chemistry, The King’s Buildings,

David Brewster Road, Edinburgh EH9 3FJ, UK

This overview summarizes three complementary strands of our current research, all focusing on the development of novel (asymmetric) base, acid, and/or dual catalysts.

Despite the wealth of reactions catalyzed by conventional N-heterocyclic carbenes (NHCs),^[1] bis(dialkylamino)cyclopropenylidenes (BACs; a)^[2] have received little attention within the synthetic organic community.  Recently, we have developed various rare BAC-catalyzed bond transformations, including the first highly enantioselective BAC catalysis.^[3]  Indeed, the use of a new chiral BAC alone has resulted in highly asymmetric aza-Morita–Baylis–Hillman reactions at ambient temperature (up to 93% ee),^[4] whereas usually a chiral acid–base dual catalyst is employed at low temperature for high asymmetric induction; various chiral NHCs proved to be ineffective in our hands (0–38% ee).

Formally isoelectronic to carbenes, gallium in its low-oxidation state +I is under-explored, but may display both donor and acceptor properties because of a lone pair of electrons and vacant p orbitals (b).^[5]  Indeed, gallium(I) complexes have been shown to be acidic,^[6a] basic,^[6b] or ambiphilic^[6c] in a stoichiometric context.  We have anticipated that gallium(I) –in situ generated from gallium(0)– may act as an ambiphilic catalyst to activate both C(sp³) pro-electrophiles and boron-based pro-nucleophiles in view of selective C–C bond formations.  In turn, we have developed the first catalytic use of gallium(0) in organic synthesis, and have demonstrated the possibility of asymmetric catalysis.^[7.8]

Finally, we have been investigating earth-abundant & environmentally benign alkali, alkaline earth, group 13, and first-row transition metal amides (c).  LDA for instance has been used traditionally in stoichiometric quantities under kinetic control; however, metal amides could be of critical importance to activate challenging pro-nucleophiles such as unbiased olefins.  Using a ‘product-base’ approach, we have developed the first sodium^[9] amide-catalyzed C–C bond formations between various imines and unbiased or functionalized olefins through a rare formal C(sp³)–H bond activation.^[10]  We have also achieved the first example of asymmetric sodium metal amide catalysis, which is important in the context of unbiased C(sp³)–H bond functionalization.