Question

What is a retro Diels Alder reaction?

Answer 1

It is literally the (microscopic) reverse direction of the Diels-Alder.

A relatively simple but interesting example is the cracking of the cyclopentadiene dimer:

The arrows are pretty much the reverse of what the forward direction shows. Instead of making two `"C"-"C"` bonds, you break two.

This is a good way, for instance, of generating usually unstable compounds in a rigged fashion such that they are not so unstable.

https://upload.wikimedia.org/

By the way, LTMP stands for lithium tetramethylpiperidide, and "rt" stands for "room temperature". So the example reaction can be done at `0~25^@ "C"`.