Ethyl (2-cyano-3-ethoxyacryloyl)carbamate: irreversibly thermal isomerization of a push-pull olefin

Abstract

A push-pull olefin, E-2, was prepared highly stereoselectively by reaction of ethyl (2-cyanoacetyl)carbamate, 1, with ethyl orthoformate in the presence of acetic anhydride. Forty percent of E-2 was isomerized to Z-2 after two hours of irradiation at 254 nm. All the Z-2 was isomerized back to E-2 spontaneously and irreversibly with Ea = 19.6 kcal mol -1 , ∆H ‡ = 19.0 kcal mol -1 , ∆S ‡ = -17.5 cal K -1 mol -1 , and ∆G ‡ = 24.4 kcal mol -1 . The negative entropy of activation for this isomerization indicates that the transition state has much more charge separation than the ground state. The low rotational barrier of this isomerization and very big chemical shift difference (∆δ C=C = 85.83 ppm) of two sp 2 -hybridized carbons of C=C partial double bond confirm 2 is a push-pull olefin.

Blue LED-Mediated Synthesis of 3-Arylidene Oxindoles

“…Interestingly, the internal olefin isomerization reactions of the Z -isomer are known under thermal or Mo-catalyzed reactions to obtain the E -isomer. Toward this, the isolated Z -isomers of 3-arylidene oxindoles were planned to study under thermal conditions to convert into the corresponding E -isomer.…”