142 Heterocycles with More than Two Heteroatoms: Higher Azoles (5-Membered) and Higher Azines (6-Membered)
Dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate, which is much used in Diels–Alder reactions, is prepared by the base-
catalysed dimerisation of ethyl diazoacetate, then oxidation of the resulting dihydro-tetrazine (after re-esterifi cation).
Exercises
- What are the products of the following (Diels–Alder) reactions:
(i) 1-pyrrolidinylcyclopentene with (a) 1,3,5-triazine and (b) 1,2,4-triazine;
(ii) 3-phenyl-1,2,4,5-tetrazine with 1,1-diethoxyethene? - Thiophosgene (S=CCl 2 ) reacts at low temperature with sodium azide to give a product that contains no
azide group; on subsequent reaction with methylamine this compound is converted into C 2 H 4 N 4 S – what
are the structures? - What are the products of the reaction of PhCONH 2 with DMFDMA to give C 10 H 12 N 2 O and then this with
(a) N 2 H 4 or (b) H 2 NOH? - 1,3,5-Triazine reacts with
(i) aminoguanidine [H 2 NN=C(NH 2 ) 2 ] to give 2-amino-1,3,4-triazole and with
(ii) diethyl malonate to give ethyl 4-hydroxypyrimidine 5-carboxylate. What reasonable mechanistic
sequences will rationalise these transformations?