Abstract: | X‐ray data show that the diethyl 6,13‐bis(Z)‐cyanomethylidene]‐5,5,14,14‐tetramethyl‐4,15‐dioxa‐7,12‐diazapentacyclo9.5.2.02,10.03,7.012,16]octadeca‐8,17‐diene‐10,17‐dicarboxylate is formed as the ZZ isomer and diastereomer with the (1R*,2R*,3R*,10S*,11R*,12R*,16R*) configuration. The 1H, 13C, and 15N NMR data exhibit that on standing in chloroform‐d solution, there is a spontaneous isomerization of this compound resulting in a thermodynamically stable mixture of the ZZ, ZE, EE, and EZ isomers with the same backbone. Using the 2D 1H–1H] COSY, 1H–13C] HSQC, and 1H–13C, 1H–15N] HMBC NMR techniques and quantum chemical calculations makes it possible a complete assignment of signals in the 1H, 13C, and 15N NMR spectra of each of the isomers. Such isomerization does not occur for similar compounds with the more bulky substituents at the 1,3‐oxazolidine rings. Copyright © 2016 John Wiley & Sons, Ltd. |