The following presentations have all been used to teach modern synthetic reactions in my graduate level courses, and present examples of reactions primarily in the context of natural product total synthesis. Although there is no verbal play-by-play for these lectures, hopefully they will serve as helpful sources of information.
The [3+2] Cycloaddition Reaction
The Colchicine Synthetic Problem
The Diels–Alder Reaction (Part 1)
The Diels–Alder Reaction (Part 2)