Synthesis of functionalized imidazo[4,5-e]thiazolo[3,2-b]triazines by condensation of imidazo[4,5-e]triazinethiones with DMAD or DEAD and rearrangement to imidazo[4,5-e]thiazolo[2,3-c]triazines

Abstract

Two series of functionalized imidazothiazolotriazine derivatives were synthesized via the condensation of imidazo[4,5-e]-1,2,4-triazine-3-thiones with acetylenedicarboxylic acid dimethyl and diethyl esters (DMAD and DEAD) and subsequent base-catalyzed rearrangement of the obtained imidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazines into regioisomeric imidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazine derivatives.

Regioselective synthesis of new imidazo[4,5‐e][1,3]thiazino[2,3‐c][1,2,4]triazines via reaction of imidazo[4,5‐e][1,2,4]triazinethiones with ethyl phenylpropiolate

“…As noted in our earlier work [27], the regioselectivity of the reactions of imidazotriazinethiones with dielectrophilic reagents can be different, and structures of both linear and angular types can be formed because of the presence of several nucleophilic centers in the imidazotriazinethione. However, under the optimized conditions, only the formation of an angular‐type product 3a‐h was observed.…”

“…We started synthesizing the target imidazothiazinotriazines by optimizing a model reaction of compound 1a with ethyl phenylpropiolate 2. Based on our previous work on the investigation of the reaction of imidazotriazinethiones 1 with dialkylacetylenedicarboxylates, the reference points for selecting conditions were acidic or basic catalysis [27]. Reaction in acetic acid provided linear-type products, that is, imidazo [4,5-e]thiazolo [3,2-b] [1,2,4]triazines.…”

“…Reaction in acetic acid provided linear-type products, that is, imidazo [4,5-e]thiazolo [3,2-b] [1,2,4]triazines. Reaction in alcohols and the presence of sodium alcoholates gave angular-type products, that is, imidazo [4,5-e]thiazolo [2,3-c] [1,2,4]triazines [27]. However, it turned out that the interaction of compound 1a with ethyl phenylpropiolate neither in acetic acid, even when heated (Table 1, entries 1, 2), nor in boiling methanol with acetic acid (entry 3) led to the condensation product 3a.…”

Tandem Michael addition/elimination – novel reactivity of pyridinium ylides in reaction with electron-deficient alkenes

“…10 These dipolarophiles were easily prepared via cycloaddition of imidazo[4,5- e ]-1,2,4-triazines with acetylenedicarboxylates. 11 Herein we report unexpected reactivity of pyridinium ylides in reaction with annulated 4-oxothiazolidin-5-ylidenes acetates to afford Michael addition/elimination products.…”

One‐pot regioselective synthesis of new imidazo[4,5‐e]thiazolo[3,2‐b][1,2,4]triazines by reaction of imidazotriazines with propargyl bromide

“…The most common method for the synthesis of fused thiazoles is intramolecular cyclization of S-functionalized cyclic thioamides and thioureas. Michael adducts [12,13], S-alkyl [14,15], S-alkenyl [16], S-alkynyl [17][18][19] derivatives can act as such S-substituted substrates. Fused thiazoles have also been prepared by acid-catalyzed Dimrothtype rearrangement of N-aminothioglycolurils [20].…”