Why is a 7-endo radical cyclisation favoured over a 6-exo in this synthesis? Normally, according to Baldwin's rules, 3-exo to 7-exo cyclisations are preferred over endo cyclisations. But in the following example, a 7-endo-trig reaction is favoured over a 6-exo-trig and I am just not able to understand why. It's a real synthesis example (taken from Eur. J. Org. Chem. 2015, 2015 (15), 3240–3250). Please explain to me why the 7-endo product is favoured here.
I'm the co-first author of this paper. I want to thank Mathew Mahindaratne for the helpful and thoughtful discussion. I just want to add one more result when I was doing the synthesis, please see the attached. The beauty of total synthesis is that we never 100% sure what the product we get, but we can always find a way to explain the results.