A Colorimetric Method for Quantifying Cis‐ and Trans‐Alkenes Using an Indicator Displacement Assay

A colorimetric indicator displacement assay (IDA) amenable to high‐throughput experimentation was developed to determine the percentage of cis‐ and trans‐alkenes. Using 96‐well plates two steps are performed: a reaction plate for dihydroxylation of the alkenes followed by an IDA screening plate consisting of an indicator and a boronic acid. The dihydroxylation generates either erythro or threo vicinal diols from cis‐ or trans‐alkenes depending upon their syn‐ or anti‐addition mechanisms. Threo diols preferentially associate with the boronic acid due to the creation of more stable boronate esters, thus displacing the indicator to a greater extent. The generality of the protocol was demonstrated using seven sets of cis‐ and trans‐alkenes. Further, blind mixtures of cis‐ and trans‐alkenes were made resulting in an average error of ± 2% in the percentage of cis‐ or trans‐alkenes, and implementing E2 and Wittig reactions gave errors of ± 3%. Furthermore, we developed variants of the IDA that alter the color changes to optimize the response to the human eye.