SYNTHESIS AND THERMOLYSIS OF A CHIRAL, NON-RACEMIC IMINOAZIRIDINE

The 2-halo imidoyl chlorides 7 are obtained from the amide 5 and the 2-halo amides 6 by the action of phosphorus pen tachloride 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 diastereomeric 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 tertbutyl alcohol, eliminate hydrogen chloride or bromide from the 2-halo amidines 9a and b and (S)-9a to 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 degrees C [(E)-4:(Z)-4 = [10:]90]. The diastereomers equilibrate at 36 degrees C with (k(EZ) + k(ZE)) = (5.92 +/- 0.08).10(-5) s(-1) (K = k(EZ)/k(ZE) = 0.428 +/- 0.013). - The thermolysis of (E)- and (Z)-4 in [D-6]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 degrees C: E(a) = (115.2 +/- 0.4) kJmol(-1), IgA = (12.06 +/- 0.28), Delta H-double dagger = (112.1 +/- 0.4) kJmol(-1), Delta S-double dagger = (-23.9 +/- 0.7) JK(-1) mol(-1), Delta G(373K)(double dagger) = 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 degrees C.