Atom-by-Atom Iterative Synthetic Logic: Laying the Foundation for Programmable Automated Construction of Small Organic Molecules.

Fully automated preparation of diverse small organic molecules remains a formidable challenge due to the inherent constraints of conventional synthetic philosophies. The existing automation approaches require access to either almost unlimited kinds of chemical reagents or custom-made building blocks (BBs). Herein we propose atom-by-atom iterative synthesis (AIS) as a new synthetic logic to tackle this challenge. By viewing complex organic molecules as assemblies of single-carbon- or heteroatom-based units, AIS aims to construct molecular skeletons through iterative coupling of simple atomic-scale BBs by a unified type of reactionboron homologations. Compared with conventional approaches, the AIS strategy uses only a few types of chemical reactions and a small set of BBs, making it more suitable for automation and artificial intelligence-assisted synthetic route design. To date, enormous progresses have been made on the synthetic chemistry that serves for the purpose of AIS, such as introducing heteroatoms and sp-carbons, forming ring structures, developing thermostable carbenoid reagents, and achieving stereochemical controls. On the other hand, substantial challenges and limitations remain to be overcome for realizing fully automated construction of diverse molecules. This Outlook article describes the AIS concept, recent progress, current limitations, and future opportunities in this field.