High Pressure, Temperature, and Solvent Effects on the Rate of the Diels-Alder Reaction of Furan with N-Phenylmaleimide

Simple Synthesis of Complex Amines from the Diels–Alder Adducts of (–)-Cytisine

“…It should be noted that the calculated reaction energies for 2a + 3a = 4k + 5k are comparable to the experimentally determined enthalpy values for the Diels-Alder reaction of N-hydroxy-and N-hydroxyethylmaleimide with furfuryl alcohol. 12 Similarly, our calculated activation energy values are comparable to the experimentally found ones for the Diels-Alder reaction between furan with N-phenylmaleimide 13 as well as DFT calculated values for eight different Diels-Alder reactions. 14 In conclusion, N-benzylcytisine (2c) reacts with Nmethyl-and N-benzylmaleimides (3a and 3e) in refluxing toluene to give two endo-isomeric Diels-Alder adducts 4 with syn-and 5 with anti-orientation of the imide group with respect to the methylene group of the 3,7-diazabicyclo-[3.3.1]nonane fragment.…”

“…Single-crystal X-ray analysis unambiguously determined 3D structures of 6a and 6b (Figure 2 a,b) which are similar to the structures of the corresponding starting materials 4i and 5i (Figure 1a,c). The 1 H and 13 C NMR spectra, mass spectrometry, and elemental analysis data are consistent with the single-crystal structures of 6a and 6b. The reduction of carbonyl groups of 6c by LiAlH 4 in THF (reflux 14 h) afforded crude diamine 7 containing about 10% of unidentified impurity.…”

“…ly consistent with their molecular structures in the crystalline state. The numbers of signals in the 13 C NMR spectra of 4i, 4j and 5i, 5j correspond to their structures, however, no assignments of those signals have been carried out. Since the structures of compounds 4i, 4j and 5i, 5j had been unambiguously confirmed by single-crystal X-ray analysis, their 2D NMR stereochemical studies in solutions were not carried out.…”

“…NMR spectra were recorded on a Varian Gemini 2000 using an internal deuterium lock. Chemical shifts () of 1 H and 13 C nuclei are measured in parts per million (ppm) relative to TMS as an internal standard. LC-MS and GC-MS spectra were recorded on an Agilent 1100 LCMSD SL instrument (electrospray ionization (ESI)) or Agilent GC7820A/MSD5977B system [electron impact ionization (EI), ionization energy 70 eV].…”

“…(dd, J = 10.9, 2.4 Hz, 1 H), 2.76 (dd, J = 12.5, 2.2 Hz, 1 H), 2.09 (dt, J = 7.1, 3.3 Hz, 1 H), 2.01-1.68 (m, 4 H), 1.72-1.53 (m, 1 H), 1.39 (ddd, J = 13.8, 10.4, 4.6 Hz, 1 H). 13 C NMR (CDCl 3 , 101 MHz):  = 177. 13, 176.46, 173.22, 60.81, 53.63, 49.71, 47.19, 46.17, 42.89, 38.77, 33.18, 30.14, 26.58, 26.37, 25.11, 19. This compound was prepared from 5j (1 g, 2.1 mmol) according to the general procedure.…”