91076-36-7Relevant academic research and scientific papers
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
stereochemistry of Ring Opening of Aziridinones (α-Lactams)
Quast, Helmut,Leybach, Holger
, p. 2105 - 2112 (2007/10/02)
The chiral, non-racemic aziridinone (R)-4 (e.e.92percent) reacts with magnesium halides to afford the α-halo amides (S)-3a (e.e. 88.8percent), (S)-3b (e.e. 89.0percent), and (S)-3c (e.e. 88.2percent) in high yields.Acid-catalyzed hydrolysis of (R)-4 in aqueous acetone yields 74percent of the α-hydroxy amide (S)-3d (e.e. 88.0percent).Methanolysis of (R)-4 in methanol at 60 deg C followed the first-order rate law with k = 1.53 * 10-5s-1 yielding quantitatively a 82:18 mixture of the α-methoxy amide (S)-3e (e.e. 89percent) and the α-amino ester (R)-14 (e.e. 87percent) when (R)-4 reacts with sodium methoxide and methanol in ether while only the former is formed (e.e. 88.2percent) byslow methanolysis in the presence of a catalytic amount of 4-toluenesulfonic acid.The absolute configurations of the major enantiomers derived from (R)-4 are based on the retention on a Chirasil-L-Val capillary gas chromatography column, CD spectra, and the comparison with authentic samples of (S)-3a, obtained from (S)-tert-leucine and (S)-3d.The results demonstrate that the N-C(3) bond of the aziridione (R)-4 is cleaved by nucleophiles with a high degree of stereospecificity and inversion of configuration.This stereochemical course is at variance with that inferred from the methanolysis of the similar aziridinone (R)-7. - Treatment of (R)-4 in methanol with one equivalent of 3-chloroperbenzoic acid (15) containing 5percent of 3-chlorobenzoic acid (16) affords carbon monoxide and the racemic oxaziridine 18 in quantitative yield, which is also obtained from the imine 19 in a very fast reaction.The acid 16 effects slow decomposition of (R,S)-4-into carbon monoxide and imine 19, probably by general acid catalysis.The stereochemical result obtained from (R)-4 as well as the reaction conditions and differences in rate for formation and epoxidation of 19 suggest that in the peracid oxidation of an aziridinone the sequence of events consists of a rate-limiting, acid-catalysed decomposition into carbon monoxide and an imine, followed by very fast epoxidation of the latter.The previous mechanism, invoking as intermediates alleged aziridinone N-oxides, e.g. 17, is not supported by the present study. Key Words: Aziridinones, chiral, non-racemic / α-Lactams / Butanoic acids, 2-substituted 3,3-dimethyl- and derivatives / Perbenzoic acid, 3-chloro- / Oxaziridines / Cycloreversion Acid catalysis, general / Ethanol, (R)-1-(9-anthryl)-2,2,2-trifluoro- / Circular dichroism
