Steric Parameterization Delivers a Reciprocally Predictive Model for Substrate Reactivity and Catalyst Turnover in Rh-Catalyzed Diyne-Alkyne [2+2+2] Cycloadditions

The Rh-catalyzed [2 + 2 + 2] cycloaddition of diynes and alkynes is a synthetically useful transformation that rapidly constructs complex scaffolds and has been used extensively for >70 years. Despite this utility, substrate reactivity issues persist, which are not mechanistically defined. Here, we provide a general predictive model for reactivity and turnover for this reaction. Contrary to the proposed electronic model, this is a predominately sterically driven process where productive turnover is proportional to alkyne steric parameters. This model allows for a priori prediction of catalyst loading, turnover, and reaction yield based on a simple assessment of the steric parameter (e.g., A-value) of the alkyne. The relationship is reciprocal, allowing A-values to be calculated from observed turnover.

Automated summary

This article presents a predictive model for the reactivity and turnover of the Rh-catalyzed [2 + 2 + 2] cycloaddition of diynes and alkynes. Contrary to the proposed electronic model, this model suggests that the reaction is predominantly driven by steric effects, and turnover is proportional to alkyne steric parameters. The model allows for the prediction of catalyst loading, turnover, and reaction yield based on the assessment of the alkyne's steric parameter.