Hydrogen isotopically labelledc ompoundsa re essential diagnostic tools in drug research and development, as they provide vital informationa bout the biological metabolism of drug candidates and their metabolites. Herein we report ap hotoredox-initiated hydrogen atom transfer(HAT) protocol which efficiently and selectively introduces deuterium or tritium at C(sp 3)ÀHb onds, utilizing heavy water (D 2 Oo rT 2 O) as the hydrogen isotope source, and ag uanidine base.T his protocol has been successfully appliedto the incorporationo fd euteriumi ns everal amino acids (lysine, glycine and proline) and small peptides. Finally,t he method has been applied to tritium,b ecause tritium-labelled peptides are essential for application in biological experiments,s uch as ligand-binding assays,o ra bsorption, distribution, metabolism, and excretion (ADME) studies.

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A new and efficient synthesis of pyridine‐based heteroaromatic boronic acid derivatives is reported through a novel diboration/6π‐electrocyclization strategy. This method delivers a range of functionalized heterocycles from readily available starting materials.

A range of functionalized heteroaromatic boronic acid derivatives are readily accessed by a diboration/6π-electrocyclization sequence. This study revealed the surprising observation that there is a direct relationship between oxime ether stereochemistry and reactivity towards electrocyclization. Specifically, E-oxime ethers are found to be significantly more reactive than their Z-counterparts (stereochemistry relative to azatriene scaffold). In contrast, the configuration at the azatriene alkene terminus has little impact on reaction rates. Computational analysis offers a rationale for this observation; a N →C=C π* orbital interaction lowers the energy of the transition state in the electrocyclization of E-oxime ethers. Finally, unreactive Z-oxime ethers can be converted to the corresponding heterocyclic products by a photolytically promoted E→Z isomerization and electrocyclization sequence.

The greater geometric lability of hydrazones over oxime ethers is used as a basis to overcome the reluctance of Zoxime ether azatrienes to undergo electrocyclization towards the synthesis of borylated (heteroaromatic) pyridines and ring-fused analogs. Such hydrazones now allow access to previously inaccessible tri-and tetrasubstituted 3-borylpyridines in high yields.The prominence of heteroaromatic motifs in pharmaceutical agents, agrochemicals and functional materials has motivated synthetic chemists to devise new strategies for the efficient and selective incorporation of these fragments into a broad range of molecular scaffolds. In this regard, boronic acid chemistry provides one of the most widely used approaches Scheme 1. Dependence of electrocyclization efficiency on oxime ether stereochemistry for the coupling of heteroaromatic systems because of the synthetic versatility of these compounds. 1