One-Pot Conversion of Aldehydes and Aryl Halides to Disubstituted Alkynes via Tandem Seyferth–Gilbert Homologation/Copper-Free Sonogashira Coupling

Design and synthesis of a clickable, photoreactive amino acid p-(4-(but-3-yn-1-yl)benzoyl)-l-phenylalanine for peptide photoaffinity labeling

Photoaffinity labeling is a powerful technique to investigate the interactions between bioactive peptides and their targets. To construct a peptide-derived photoaffinity probe, at least two amino acids need to be modified or replaced, increasing experimental difficulties and negatively affecting activity. Herein, we report the synthesis of a clickable, photoreactive amino acid p-(4-(but-3-yn-1-yl)benzoyl)-l-phenylalanine (Abpa) and its Fmoc-protected version from 3-(4-bromophenyl)-1-propanol in 11 steps with an overall 12.5% yield. The amino acid contains both a photoreactive benzophenone and a clickable terminal alkyne which acts like a reporter tag by fast attachment to other functional groups via 'click' reaction, and a photoaffinity probe could be created by one single amino acid substitution during peptide synthesis. And its small size helps to retain bioactivity. The efficiency of Abpa was demonstrated by photoaffinity labeling experiments using photoactivatable probes of α-conotoxin MI.

Pd-Catalyzed Cross-Couplings: On the Importance of the Catalyst Quantity Descriptors, mol % and ppm

This Review examines parts per million (ppm) palladium concentrations in catalytic cross-coupling reactions and their relationship with mole percentage (mol %). Most studies in catalytic cross-coupling chemistry have historically focused on the concentration ratio between (pre)catalyst and the limiting reagent (substrate), expressed as mol %. Several recent papers have outlined the use of “ppm level” palladium as an alternative means of describing catalytic cross-coupling reaction systems. This led us to delve deeper into the literature to assess whether “ppm level” palladium is a practically useful descriptor of catalyst quantities in palladium-catalyzed cross-coupling reactions. Indeed, we conjectured that many reactions could, unknowingly, have employed low “ppm levels” of palladium (pre)catalyst, and generally, what would the spread of ppm palladium look like across a selection of studies reported across the vast array of the cross-coupling chemistry literature. In a few selected examples, we have examined other metal catalyst systems for comparison with palladium.

Facile one-pot synthesis of diarylacetylenes from arylaldehydes via an addition-double elimination process

A practical one-pot protocol has been developed to synthesize diarylacetylenes from arylaldehydes by treatment with 1-(arylmethyl)benzotriazoles and LiN(SiMe3)2. The reaction proceeded through imine formation, Mannich-type addition and double elimination to deliver products in up to 99% yields with broad substrate scope. In addition, gram-scale synthesis of 1-bromo-4-(phenylethynyl)benzene has been demonstrated.