Manipulating Reaction Energy Coordinate Landscape of Mechanochemical Diaza-Cope Rearrangement

Abstract

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.

Perspective: Path Sampling Methods Applied to Enzymatic Catalysis

“…5. Putative reaction coordinate degrees of freedom can be identified and verified in committor distribution analysis by the variability of the separatrix, neural network prediction, likelihood maximization, , energy flux, , or for that matter trial and error of amino acid residues near the reacting atoms. In trial and error, the first attempt is always simply the atoms being transferred in any reaction; if this does not result in an appropriately peaked distribution of about 5, more degrees of freedom are added.…”

Reshuffle Bonds by Ball Milling: A Mechanochemical Protocol for Charge-Accelerated Aza-Claisen Rearrangements

“…For instance, the first protocols for main group, Lossen, or Beckmann rearrangements were reported in the last ten years [ 114 , 115 , 116 , 117 , 118 ]. However, the extension to sigmatropic rearrangement reaction was still missing until Yan and coworkers recently reported about a mechanochemical diaza-Cope rearrangement that significantly outstrips the reaction rate of other protocols that are conducted under solution, neat or sonication conditions [ 119 , 120 ].…”