We then defined the target chemical transformation, highlighted in green in Fig. , to initiate the search of analogue routes. The searching led to three routes. Routes-1 and -2 were single step reactions, but both contained an unfavoured phenylphosphine derivative (PPh3A). The analogue route-3 was more appealing considering its solvents and reagents, as well as its high molecular similarity with respect to the starting and the target molecules. Thus, a new route from BPA to BocPP was proposed, see the bottom of Fig. . To define a chemical transformation, selection of a substructure could be tricky, since both the number and quality of results are sensitive to atoms included. If the substructure selection included too many atoms, i.e., a very specific substructure, no qualified analogue routes can be found. Whereas a "loose" definition of chemical transformation with only a few atoms, (e.g., from -Cl to -OH), may lead to a very large number of routes, from which one can hardly find routes that suite the target chemical transformation.