Selective Reduction of Esters to Access Aldehydes Using Fiddler Crab-Type Boranes.

The partial reduction of esters to aldehydes is a fundamentally important transformation for the synthesis of numerous fine chemicals and consumer goods. However, despite the many efforts, limitations have persisted, such as competing overreduction, low reproducibility, use of exigent reaction conditions and hazardous chemicals. Here, we report a novel catalyst family with a unique steric design which promotes the catalytic partial reduction of esters with unprecedented, near-perfect selectivity and efficiency.

Bioinspired Synthesis of (-)-Hunterine A: Deciphering the Key Step in the Biogenetic Pathway.

A concise, bioinspired, and enantioselective synthesis of (-)-hunterine A, an odd 6/7/6/6/5 pentacyclic natural product, is described. The key step in the synthesis of this complex structure is an interim-template directed 6-exo selective epoxide ring-opening reaction, which is interwoven with a hydrolysis step of the indolenine hemiaminal template to create the unusual 7-membered azepine bridge motif. Our work not only refines the previously proposed biogenetic pathway, but also reveals the possible stereochemical prerequisite of the unique skeletal rearrangement, which provides a vantage point for understanding how (-)-hunterine A is likely to be generated in nature.

Emerging Conformational-Analysis Protocols from the RTCONF55-16K Reaction Thermochemistry Conformational Benchmark Set.

RTCONF55-16K is a new, reactive conformational data set based on cost-efficient methods to assess different conformational analysis protocols. Our reference calculations underpinned the accuracy of the CENSO (Grimme et al. , 2021, 125, 4039) procedure and resulted in alternative recipes with different cost-accuracy compromises.

Total Synthesis and Structural Plasticity of Kratom Pseudoindoxyl Metabolites.

Mitragynine pseudoindoxyl, a kratom metabolite, has attracted increasing attention due to its favorable side effect profile as compared to conventional opioids. Herein, we describe the first enantioselective and scalable total synthesis of this natural product and its epimeric congener, speciogynine pseudoindoxyl. The characteristic spiro-5-5-6-tricyclic system of these alkaloids was formed through a protecting-group-free cascade relay process in which oxidized tryptamine and secologanin analogues were used.