Synthesis of the dichlorobisoxazole-indole portion of the antitumor agent diazonamide by a putative biogenetic strategy

Chlorination of the bis-oxazole-indole 16 using N-chlorosuccinimide gave the dichloride 13 (86%) and the trichloride 12 (5%) thus completing the synthesis of the CDEF rings of diazonamide.