Regioselectivity of aryl radical attack onto isocyanates and isothiocyanates. Issue 46 (14th November 2018) - Weragoda, Geethika K.
Abstract : Regioselectivity of attack by the N -methyl-pyridinium-4-yl radical cation onto RNCX (X = O and S) depends on R and X. Abstract : The combination of multistage mass spectrometry experiments employing the distonic radical approach together with DFT calculations are used to examine addition of the N -methyl-pyridinium-4-yl radical cation (γ-NMP ) to iso(thio)cyanates in the gas-phase. The type of products formed depend on the nature of the iso(thio)cyanate: (1) hydrogen atom abstraction occurs for alkyl isocyanates; (2) aryl isocyanates undergo radical- ipso substitution; (3) radical attack occurs at the CC bond of allyl isocyanate; (4) radical attack occurs at the CS bond of isothiocyanates to generate S adducts ofγ-NMP and isonitriles. DFT calculations provide insight into the reactivity differences of these heterocumulenes towards the electrophilic C-centered γ-distonic radical cations. Translation of these gas phase results to the solution phase were hampered by dominating radical recombination reactions which appear to be favoured over the radical-iso(thio)cyanate reactions.