[TheUnassuming]

Yes, I think you are dead on with why the acid helped move the reaction forward.  I was reluctant to try it initially due to assumptions that it would frag like the mom substrate.   Then I got desperate/bored as I was going back and running the protecting group swap route... good thing too!

The fragmentation primarily comes from the breaking of a phosphate bioisostere on the scaffold, which has been a source of instability throughout the project.  Can go more into detail once the paper is accepted :-).