Question

why does furan participate in diels alder reaction more readily than pyrrole

Answer 1

furan is less aromatic than pyrrole, so it much more readily acts like a diene.

to see this, consider what it takes to force furan and pyrrole into an aromatic configuration.

for pyrrole, the amine nitrogen's lone pair has to delocalize across the pi system. the nitrogen has to leave its normal sp3 configuration and adopt an sp2 so the lone pair can fill a p orbital and be co-planar with the rest of the pi system. then and only then does the ring get its 6 electrons. the nitrogen doesn't mind adopting an sp2 configuration -- it happens often enough (even in things like amides, the amide nitrogen adopts an sp2 config fairly readily). and it certainly doesn't mind sharing its lone pair. in fact it's ability to donate a lone pair is essentially what controls all of the amine's chemistry.

so pyrrole is "pretty aromatic."
Hope it helps