Aryne Chemistry: Generation Methods and Reactions Incorporating Multiple Arynes

Arynes hold significance for the efficient fusion of (hetero) arenes with diverse substrates, advancing the construction of complex molecular frameworks. Employing multiple equivalents of arynes is particularly effective in the rapid formation of polycyclic cores found in optoelectronic materials and bioactive compounds. However, the inherent reactivity of arynes often leads to side reactions, yielding unanticipated products and underlining the importance of a detailed investigation into the use of multiple arynes to fine-tune their reactivity. This review centers on methodologies and syntheses in organic reactions involving multiple arynes, categorizing based on mechanisms like cycloadditions, σ-bond insertions, nucleophilic additions, and ene reactions, and discusses aryne polymerization. The categorization based on these mechanisms includes two primary approaches: the first entails multiple aryne engagement within a single step while the second approach involves using a single equivalent of aryne sequentially across multiple steps, with both requiring strict reactivity control to ensure precise aryne participation in each respective step. Additionally, the review provides an in-depth analysis of the selection of aryne precursors, organized chronologically and by activation strategy, offering a comprehensive background that supports the main theme of multiple aryne utilization. The expectation remains that this comprehensive review will be invaluable in designing advanced syntheses engaging multiple arynes.

Development of 3-triazenylaryne and its application to iterative aryne reactions via o-triazenylarylboronic acids

Herein, a novel aryne species, 3-triazenylaryne, was developed and its regioselectivity was revealed. Based on the regioselectivity, various alkyne moieties were introduced by iodoalkynylation, and further derivatization to o-triazenylarylboronic acids as 3-alkynylaryne precursors was enabled. Therefore, 3-triazenylaryne was developed as a divergent platform for the generation of various 3-alkynylarynes.

Synthesis of Multisubstituted Aromatics via 3-Triazenylarynes

An efficient method for generating 3-triazenylarynes from ortho-iodoaryl triflate-type precursors was developed. The generated arynes reacted with various arynophiles with high regioselectivity because of the triazenyl group. The 3-triazenylaryne precursors functioned as useful intermediates of diverse multisubstituted aromatic compounds through the transformation of the remaining triazenyl group of aryne adducts and triazenyl group-directed ortho-C-H functionalization.

Oxidative Cycloaddition Reactions of Arylboron Reagents via a One-pot Formal Dehydroboration Sequence

Arylboron compounds are widely available and synthetically useful reagents in which the boron group is typically substituted. Herein, we show that the boron group and ortho-hydrogen atom are substituted in a formal cycloaddition reaction. This transformation is enabled by a one-pot sequence involving diaryliodonium and aryne intermediates. The scope of arylboron reagents and arynophiles is demonstrated, and the method is applied to the formal synthesis of an investigational drug candidate.

Manipulating Reaction Energy Coordinate Landscape of Mechanochemical Diaza-Cope Rearrangement

Chiral vicinal diamines, a unique class of optically-active building blocks, play a crucial role in material design, pharmaceutical, and catalysis. Traditionally, their syntheses are all solvent-based approaches, which make organic solvent an indispensable part of their production. As part of our program aiming to develop chemical processes with reduced carbon footprints, we recently reported a highly practical and environmentally-friendly synthetic route to chiral vicinal diamines by solvent-free mechanochemical diaza-Cope rearrangement. We herein showed that a new protocol by co-milling with common laboratory solid additives, such as silica gel, can significantly enhance the efficiency of the reaction, compared to reactions in the absence of additives. One possible explanation is the Lewis acidic nature of additives that accelerates a key Schiff base formation step. Reaction monitoring experiments tracing all the reaction species, including reactants, intermediates, and product, suggested that the reaction profile is distinctly different from ball-milling reactions without additives. Collectively, this work demonstrated that additive effect is a powerful tool to manipulate a reaction pathway in mechanochemical diazo-Cope rearrangement pathway, and this is expected to find broad interest in organic synthesis using mechanical force as an energy input.