Brute force application, Filtering, and Prioritization Figure : Substrates from the literature for which named ring-forming reactions were known (substrates for which predictions failed are shown in Figures and). These were used to compare the performance of 'Ring Breaker' with our standard retrosynthetic model. The substrates were chosen such that there was limited functionality apart from the ring system, to emulate the simplified structures on which a ring-forming reaction may be necessary. Additionally, the simple substrates chosen allowed for evaluation of the two models 'Ring Breaker' and the standard model for their performance on ring formations. The additional functionality present in more complex structures can detract from the ring-forming task as outlined in this paper.