Synthesis of fused dihydropyrido[e]purines via ring closing metathesis

Ring closing metathesis (RCM) of 8,9-diallylpurines or 9-butenyl-8-vinylpurines with the Grubbs 2nd generation catalyst resulted in fused 6,9- or 8,9-dihydropyrido[e]purines, respectively. The 8,9-dialkenylpurines were prepared from 8-bromopurines after 9-alkenylation and subsequent Stille coupling at C-8 with alkenylstannanes in the presence of Pd(PPh3)4 or Pd(PPh3)2Cl2.