Late-stage diversification of chiral N-heterocyclic-carbene precatalysts for enantioselective homoenolate additions.

A library of chiral triazolium salts has been prepared by late-state diversification of a triazolium amine salt. By utilizing a primary amine as a functional handle, a single triazolium salt can be transformed into a variety of chiral N-heterocyclic carbene precatalysts. This approach makes the preparation of chiral N-heterocyclic carbenes possible by a single-step modification of a triazolium salt, rather than the usual need for multistep organic synthesis and challenging heterocycle formation for each member of a catalyst library. We have screened these catalysts for control of diastereo- and enantioselectivity in a γ-lactam-forming reaction between α,ß-unsaturated aldehydes and cyclic ketimines.

N,N'-Bis(1-ethynylcyclo-hexyl)-pyro-mellitic diimide.

The title compound, C(26)H(24)N(2)O(4), consists of a symmetrical mol-ecule that lies across a crystallographic inversion centre. The C-C distance in the triple bond is 1.188 (2) Šand there is also an inter-molecular C-H⋯O contact from a terminal acetyl-ene C-H to one of the dimiide O atoms [3.4349 (19) Å].

N,N'-Bis(1-acetyl-cyclo-hexyl)-1,8:4,5-naphthalene-tetra-carboximide.

The title compound, C(30)H(30)N(2)O(6), has crystallographic inversion symmetry with the nitro-gen atom and the two oxygen atoms of the naphthalene diimide system deviating by -0.243 (2), 0.109 (3) and 0.247 (2) Å, respectively, from the plane defined by the carbon atoms.

An expedient synthesis of mellitic triimides.

Heating of the solid ammonium salts obtained from treatment of mellitic acid with 3 equiv of a primary amine yields trisubstituted mellitic triimides via dehydration and imide ring closure. This surprisingly simple synthetic approach is amenable to incorporation of alkyl, aryl, and amino acid ester substituents, thereby opening broad access to a family of C(3)-symmetric organic electron acceptors.