Regioselectivity of aryl radical attack onto isocyanates and isothiocyanates

• Published in: Organic & biomolecular chemistry Vol. 16; no. 46; pp. 9011 - 9020
• Main Authors: Weragoda, Geethika K, Pilkington, Rowan L, Polyzos, Anastasios, O'Hair, Richard A J
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 28.11.2018
• Subjects: Adducts; Aromatic compounds; Cations; Cyanates; Isocyanates; Mass spectrometry; Mass spectroscopy; Mathematical analysis; Pyridinium; Recombination; Recombination reactions; Regioselectivity; Vapor phases
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/c8ob02209g

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[double bond, length as m-dash]C bond of allyl isocyanate; (4) radical attack occurs at the C[double bond, length as m-dash]S bond of isothiocyanates to generate S adducts of γ-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.