Insights into the reactivity of 2-hydroxycyclobutanones with thiols corroborated by quantum chemical DFT investigations, NMR and Raman analysis

A general strategy for the synthesis of 2-substituted cyclobutanone sulphides via a tandem Brønsted acid catalysed nucleophile addition/ring-contraction/C3-C4 ring-expansion reaction sequence has been exploited. The procedure led to a wide panel of four membered cyclic ketones in good to excellent yields and with broad substrate scope. Mechanistic aspects and kinetic parameters were investigated by quantum chemical DFT calculations allowing us to rationalize the different reactivity of 2-aryl- and 2-alkyl- substituted 2-hydroxycyclobutanones towards thiol nucleophiles in reactions mediated by sulphonic acids. NMR and in situ Raman techniques, were employed to better understand the reaction kinetics and parameters that affect the desired outcome.