This excellent paper from BMS describes a method for predicting the process mass intensity (PMI) for a given chemical step or for a whole synthesis, and thus provides a new way to compare synthetic routes even at the design stage. At the heart of this approach is an internal database of PMI scores for 15 common reaction types (see Table 1). There is a PMI range for each reaction type which will reflect whether it is an early stage unoptimized process through to a fully optimized late stage development process. Several real-life examples are used to explain how the method works including one example where the choice of synthetic route would have changed had this tool been available. In essence the synthetic route used in later development was initially rejected and an alternative synthetic route was used in early development, but, if this tool had been available the late stage route would have been used at the start of the project.
Table 1: Top 15 Reaction Types
C-C coupling, Suzuki
J. Li, E.M. Simmons, and M.D. Eastgate,* Green Chem., 2017, 19, 127-139.