Reactions of ethyl cyanoformate with cycloimmonium salts: a direct pathway to fused or substituted azaheterocycles

Insights on the Chemical Behavior of Ethyl Cyanoformate: Dipolarophile, Cyano or Ethoxycarbonyl Source

“…Instead, quinolinium bromide 4 n reacted with the cyanide anion from salt 8 (Scheme ) to give nitrile 4 na . Now, triethylamine generates molecule 4 nb which, after deprotonation, provides allylic anion 4 nc , from which air promoted oxidation leads to quinolone 9 (Scheme ), and this reactivity is similar to that already described for few examples of phenanthroline, quinoline and phtalazine salts …”

“…The main syntheses of imidazo[1,2‐ a ]pyridines reported in the literature are based on modifications of 2‐aminopyridines . The [3+2] cycloaddition of cycloimmonium ylides with the nitrile group of ethyl cyanoformate has been recently reported to obtain azaindolizines . This latter procedure was adapted in the current study for the synthesis of azaindolizines of general structure 1 .…”

“…The previous study dealing with the reactivity of pyridinium salts in presence of ethyl cyanoformate under basic conditions concluded that the unsubstituted pyridinium salts are not suitable for obtaining cycloadducts, leading to many decomposition products. In this study, [3+2] dipolar cycloaddition of cycloimmonium salts 4 a ‐ k with ethyl cyanoformate furnished target products 1 a‐k in good yields (Scheme ).…”

“…It is known that ethyl cyanoformate can react with triethylamine to generate salt 8 (Scheme ) and this led to a difference in reactivity between iso quinolinium 4 g (Scheme ) and quinolinium 4 n salts (Scheme ). The first one readily underwent the expected [3+2] cycloaddition to furnish azaindolizine 1 g , while the formation of an ylide from the quinolinium salt 4 n did not occur quickly.…”

“…To access the target azaindolizines 1 , a [3+2] cycloaddition reaction was privileged. Recently, a new cyclization of cycloimmonium ylides with the nitrile group of ethyl cyanoformate has been reported and has the advantage of providing an ester function on the position 2 of the target azaindolizines . This manuscript concluded that unsubstituted pyridinium salts did not allow obtaining cycloadducts, leading to many decomposition products.…”