There is no noteworthy connection between the two concepts. Consider the following four judgements involving primitive and non-primitive notions according to Euclidean geometry and using a priori according to Kant. The judgements cover all possible combinations:
- primitive notion in a-priori judgement
- non-primitive notion in a-priori judgement
- primitive notion in a-posteriori judgement
- non-primitive notion in a-posteriori judgement
"The angular sum in a triangle is 180°" involves the non-primitive notion of triangle and is (synthetic) a priori.
"A straight line can be drawn from any point to any point" involves the primitive notion of point and is (synthetic) a priori.
"The very triangle I have just drawn has a bigger area than the one I drew yesterday" involves the non-primitive notion of triangle and is a posteriori (and thus synthetic).
"The straight line I drew yesterday at 10am is longer than the straight line I drew today at 10am" involves the primitive notion of straight line and is a posteriori (and thus synthetic).