91076-36-7Relevant articles and documents
Synthesis and Thermal Reorganisations of Iminoaziridines. Ab Initioo Calculations of Their Transition States, of Diazatrimethylenemethanes, and Some Cyclic Members of the C2H4N2 Potential-Energy Hypersurface
Quast, Helmut,Aldenkortt, Sven,Schaefer, Peter,Schmitt, Edeltraud,Wuerthwein, Ernst-Ulrich
, p. 2171 - 2188 (2007/10/03)
2-Iminoaziridine 19 and the pairs of isomers 22/23 and 32/33 can be obtained in high yields by base-induced 1,3-dehydrohalogenation of the corresponding α-halo amidines.Regioselectivity of the ring closure reaction of 21 is achieved by treatment with potassium hydride as base in the presence of 18-crown-6 to afford almost exclusively 23.At low temperatures, the cyclisation of 21a under the influence of potassium tert-butoxide occurs diastereoselectively yielding (Z)-22 and (Z)-23 (87:13).Resolution of racemic 21a can be attained by single recrystallisation of the nicely crystallised mandelates of the like configuration, thus providing an efficient route to (R)- and (S)-23 of high enantiomeric purity.Chiroptical data are reported for 21a and 23. - (E)- and (Z)-22 equilibrate faster by more than one order of magnitude than (E)- and (Z)-23 but almost the same preference for the E diastereomer is found in both cases. - Only first-order decomposition into isocyanides 6 and imines is observed on thermolysis of 19, 22, 23, and 32 with activation parameters depending on the substitution pattern.In contrast, the thermal valence isomerisation 35 -> 36 is fast enough to complete with the cycloreversion of 35.Thermal racemisation of (R)-23 does not occur.Quantum-chemical calculations were performed on the parent iminoaziridines (E)- and (Z)-38, 3-amino-2H-azirine (39), the methylenediaziridines cis- and trans-40, and diastereomeric closed-shell and open-shell planar (41) and (open-shell) "mono-orthogonal" diazatrimethylenemethanes 42, 43.Complete geometry optimisations were appropriately performed with the RHF/6-31+G** and the UHF/6-31+G** basis sets.Energies of the closed-shell states were calculated on the RHF, MP2, MP4SDTQ, and CCSD(T) levels, those of open-shell states on the UHF, UMP2, UMP4SDTQ, and CCSD(T)/UHF levels. - (E)-38, being lowest in energy of the parent iminoaziridines (Erel = 0.0), equilibrates with (Z)-38 via an almost linear transition state (Erel = 113.4 kJ mol-1) and decomposes into hydrogen isocyanide and formaldimine in a one-step cheletropic process rel = 179.8 kJ mol-1, CCSD(T)/RHF> with a highly unsymmetrical transition state in which the N1-C2 bond is almost completely broken whereas the C2-C3 bond is still strong.The same is true for the cheletropic decomposition of (Z)-38 the transition state of which (Erel = 168.2 kJ mol-1) is even lower by 11.6 kJ mol-1. - Energy-rich zwitterionic transition states are found with the RHF method among which 1A'-(E,Z)-41 is lowest in energy rel = 203.0 ... - Keywords: Aziridines, 2-imino-, chiral, non-racemic; Amidines, N,N'-dialkyl-2-halo-; 1,3-Dehydrohalogenation, regioselectivity and diastereoselectivity of; E/Z Diastereomerisation; Cycloreversion of isocyanides and imines; Valence isomerisation; Calculations, high-level ab initio, RHF, UHF, MPn, CCSD(T); 2H-Azirine, 3-amino; Diaziridine, 3-methylene; Diazatrimethylenemethanes, diastereomeric, closed-shell and open-shell; Reorganisations, transition states of thermal
