Synthesis and Transformations of Urazoles Derived from 7,7‐Dicarboxynorcaradiene: Formation of 2,4‐Dioxohexahydro‐1,3,5‐Triazines by an Unusual Base‐Catalyzed Rearrangement

Abstract

Abstract 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione (PTAD) or 4‐methyl‐1,2,4‐triazoline‐3,5‐dione (MTAD) cycloaddition to the 7‐cycloheptatrienecarboxylates gave the endo ‐urazoles 1 . With the 7,7‐cycloheptatrienedicarboxylates 5 the urazoles 6 were formed. Decarboxylation of urazole 6c led to endo ‐ 1b isomer. Attempts to isomerize endo ‐ 1b and endo ‐ 1c by base catalysis, afforded after methylation with methyl iodide the 2,4‐dioxohexahydro‐1,3,5‐triazine derivatives 2a, b . This unusual rearrangement also took place with urazole 3 leading to 1,3,5‐triazine 4 , but the urazoles derived from butadiene and cyclopentadiene did not respond 1 H NMR differential NOE and X‐ray analysis of 2b and 6c were necessary for the structural elucidation of the 1,3,5‐triazines 2a, b .