Behaviour of Cyclopropanes Bearing Capto‐Dative Substitution Upon Electron‐Impact and Flash‐Vacuum Pyrolysis Conditions

Abstract

AbstractTandem mass spectrometry has been applied to investigate the behaviour of bis‐captodative (cd) substituted cyclopropanes NC(SR)CCH2C(SR)CN [1, R=CH3; 2, R=tBu and 3, R=C6H5] upon electron impact (EI) and flash‐vacuum pyrolysis (FVP) conditions. Ring‐opening of the molecular ions of 1 followed by a 1,2‐hydrogen shift preceedes the fragmentation consisting mainly in the competitive losses of CH3S and CH2S. The least energy demanding reaction is however a methyl loss requiring also ring cleavage. The m/z 70 base peak is ascribed to cyanothioacylium ions (N=C‐=S) as indicated by the characteristic fragmentations induced by collision. Upon FVP conditions 1decays to the cd olefin 8 and the carbene 9 in competition with the extrusion of CH3S. and CH3. radicals at the highest temperatures. The behaviour of 2 upon both conditions is dominated by the chemistry of the t‐butyl substituents.Ring cleavage of the molecular ions of 3 preceedes also the fragmentation and induces rearrangement reactions yielding unexpected cyclohexadiene thione ions and C7H7+ ions. Upon FVP, C‐S bond homolysis readily occurs in competition with an elimination of a carbene molecule.