A compound serving a link between citric acid cycle and urea cycle is:
The fumarate formed may be funnelled into TCA cycle to be converted to malate and then to oxaloacetate to be transaminated to aspartate. Thus, the urea cycle is linked to TCA cycle through fumarate.
Reference: Vasudevan 7th  ed, pg 204
Malate
Citrate
Succinate
Fumarate