Synthesis and Thermolysis of a Chiral, Non-Racemic Iminoaziridine11

The 2-halo imidoyl chlorides 7 are obtained from the amide 5 and the 2-halo amides 6 by the action of phosphorus pentachloride and thionyl chloride, respectively. Non-racemic (S)-6a is converted into 7a which is racemic, however. The reaction of Lawesson's reagent with 6a furnishes the diaste-reomeric 1,3,2-thiazaphospholidine derivatives 15. Treatment of (S)-6a (98% ee) with methyl triflate affords 2-chloro imidate 8 (95% ee) which reacts with methanamine in the presence of methanammonium chloride to yield the 2-chloro amidine (S)-9a (90% ee). The 2-halo imidoyl halides 7a and b react with methanamine to produce the 2-halo amidines 9a and b. — Strong bases, e.g. potassium tert-butoxide or sodium hydride in the presence of catalytic amounts of tert-butyl alcohol, eliminate hydrogen chloride or bromide from the 2-halo amidines 9a and b and (S)-9ato yield mixtures of the 2-iminoaziridines (E)- and (Z)-4, and (E,R)- and (Z,R)-4 (83% ee), respectively. The 1,3-elimination of hydrogen bromide from 9b is diastereoselective at -30 to -40° [(E)-4:(Z)-4 = 90]. The diastereomers equilibrate at 36° with (kEZ + kZE) = (5.92 ± 0.08) . 10−5 s−1 (K = kEZ/kZE = 0.428 ± 0.013). - The thermolysis of (E)- and (Z)-4 in [D6]benzene solution yields the imine 16 and methyl isocyanide (17). The decomposition follows the first-order rate law. The following Arrhenius and Eyring parameters are calculated from five rate constants obtained in the temperature range of 70–110°: Ea = (115.2 ± 0.4) kJmol−1, IgA = (12.06 ± 0.28), δH‡ = (112.1 ± 0.4) kJmol−1, δS‡ = (-23.9 ± 0.7) JK−1 mol−1, δG‡373K = 121 kJmol−1. The enantiomeric excess of the surviving fraction of (E,R)- and (Z,R)-4 is unchanged after two half-lives at 80°.