Enantioselective Catalysis with Pyrrolidinyl Gold(I) Complexes: DFT and NEST Analysis of the Chiral Binding Pocket.

A new generation of chiral gold(I) catalysts based on variations of complexes with JohnPhos-type ligands with a remote C2-symmetric 2,5-diarylpyrrolidine have been synthesized with different substitutions at the top and bottom aryl rings: from replacing the phosphine by a N-heterocyclic carbene (NHC) to increasing the steric hindrance with bis- or tris-biphenylphosphine scaffolds, or by directly attaching the C2-chiral pyrrolidine in the ortho-position of the dialkylphenyl phosphine. The new chiral gold(I) catalysts have been tested in the intramolecular [4+2] cycloaddition of arylalkynes with alkenes and in the atroposelective synthesis of 2-arylindoles. Interestingly, simpler catalysts with the C2-chiral pyrrolidine in the ortho-position of the dialkylphenyl phosphine led to the formation of opposite enantiomers. The chiral binding pockets of the new catalysts have been analyzed by DFT calculations. As revealed by non-covalent interaction plots, attractive non-covalent interactions between substrates and catalysts direct specific enantioselective folding. Furthermore, we have introduced the open-source tool NEST, specifically designed to account for steric effects in cylindrical-shaped complexes, which allows predicting experimental enantioselectivities in our systems.

Rh-Catalyzed Ortho C-H Alkynylation of Aromatic Aldehydes.

The Rh(III)-catalyzed ortho-alkynylation of benzaldehydes is enabled by the transient formation of an imine as a directing group. A broad scope of substrates was obtained under mild reaction conditions, granting access to mono- and dialkynylated products. The functionalization of readily available building blocks allowed the development of modular syntheses of dibenzopentalenes, isoquinolines, indoles, and indolines.

Total Synthesis of (+)-Sarcophytin.

A total synthesis of the cembranoid (+)-sarcophytin is presented, featuring a Diels-Alder cycloaddition of an enone as the dienophile with an ester-derived dienoate. The study highlights a peculiar geometric preference for the Z dienoate to furnish the cycloadduct. The endgame involves a reaction cascade, including lactone opening, alcohol oxidation, and ketone epimerization to complete an efficient synthesis. A salient feature of the synthesis is the resulting reassignment of the absolute configuration, which corrects the previously reported nominal structure.