Intermediates int1 and int2 can undergo reductive elimination (RE) via competing TSs at internal (TS3, TS4) or external positions (TS5, TS6) (Figure ). We found reductive elimination to be the rate-and enantio-determining step, which occurs irreversibly. Reductive elimination barriers to form linear products are significantly higher, by 5.8-6.5 kcal/mol, compared to the most stable branched pathway via TS3 (predicted regioisomeric ratio exceeding 99.9% for R-prod).