Controlled keto–enol tautomerism of coumarin containing β-ketodithioester by its encapsulation in cucurbit[7]uril

Abstract

Conventional spectroscopy techniques (UV-Vis, fluorescence and NMR), mass spectrometry and molecular modeling studies are used to assess the inclusion of cucurbit[7]uril (CB7) with coumarin 7-N,N-diethylamino-2H-chromen-2-one derivatives bearing ethyl acetoacetate (CAM1) and methyl β-ketodithioester (CAM2) moieties. For the first time, it has been demonstrated that the macrocycle CB7 is able to stabilize the keto tautomeric form of both coumarin derivatives. More interestingly, it was also seen that for CAM2, the macrocycle CB7 shifts the keto–enol equilibrium from its enol form to the keto tautomer after its inclusion, establishing important differences with inclusion in β-CD, while for CAM1, the macrocycle CB7 maintains the original keto form.