The electronic effect of N-protecting groups on Diels–Alder cycloaddition reaction of furan-cored compounds

Furan-derived nitrogen side-chain molecules were used to investigate the effect of nitrogen-protecting groups on intramolecular Diels–Alder cyclization reaction yields. The protection reactions were carried out in both dichloromethane and water. The protected molecules were synthesized in dichloromethane and then cycled in toluene. On the other hand, in water as a reaction media both protection and cyclization were carried out in the same environment which provides advantages in saving time and chemicals. To study the electronic effects of protecting groups, various electron-withdrawing and electron-donating protective groups were used and their effects on cyclization were evaluated. As a result, the mesomeric electron-withdrawing and sterically large protecting groups increased the yield of Diels–Alder cycling reactions effectively. In addition, the iminium ion formed between some protecting groups and the molecule caused the formation of E/Z isomers and this was demonstrated by dynamic NMR experiments.