attaching a coupling to copper pipe very close to wood
Use a soldering mat and that will protect the wood.

If you don’t have a soldering mat, then anything that will stop direct flame contact with the wood will work - I have used non-flamnable fibre board very effectively. Good because you can cut a slot with a hole to fit around the pipe.

More of an issue will be getting that copper pipe clean and using a decent flux - I use Powerflux in those situations as it is very strong but you do need to wash it after.