SWIM was thinking of doing a THF>GBL synth as per

https://www.thevespiary.org/rhodium/Rhodium/pdf/solventfree.kmno4.oxidation.pdf

and was wondering if any other bees had an experience with this as upon taking a gander @ 2mmol of THF in relation to ~4 grams of KMnO4 and CuSO4*5H2O it became apparent that the THF would be but a drop into a pile of macerated oxiderizer.  Could anybee comment on whether this scale is wrong as SWIM was thinking of doing it 4mol THF to 1mol KMnO4 along the molar ratio lines and had a dream about the experiment that ended in him awaiting for an opportunity to distill and analyze the product. thank ye in advance.

There are other methods of doing this.

The CuSO4.5H2O supplies water for the oxidation, and may also somehow mediate the oxidation.

I recommend trying some kind of halogen-based oxidation. TCCA is the ever-popular agent for this. There's threads on the topic. Basically, doing an acidic oxidation should work, as halogen is the real oxidizing agent. Much room for research in this area.

Failing that, I could look something up for you. I have a couple papers involving this sort of oxidation.

If you want a variety of methods to GBL/GHB, try this:

Post 439780

(Aurelius: "Compilation on GHB/GBL", Methods Discourse)

SWIM's GC-MS analysis of the crude product revealed butyrolactone as 7% of final product after extraction with ethyl acetate.  distillation to follow.
it looks like a lot of the THF was simply broken up into butanol and a furan-one of undeterminable structure, which is definitely not an over-oxidized product. 
stay tuned...