Catalytic multi-step continuous-flow processes for scalable transformation of eugenol into potential fragrances

Catalytic multi-step processes were optimized and developed under continuous-flow conditions, to transform eugenol into potential new fragrances. One approach consisted in the direct catalytic conversion of eugenyl acetate into the corresponding cyclic carbonate, through a two-step protocol that utilizes two different tubular flow reactors for Mn(V)-catalysed epoxidation, using imidazole as co-catalyst and hydrogen peroxide as the oxidant, followed by the epoxide carboxylation with carbon dioxide, catalysed by a binary ZnBr2/TBAB catalytic system. With this methodology, a productivity of 7.68 g product per day was obtained. The other approach is an efficient hydroformylation/acetalization sequential process, which operates through a multi-stage flow system consisting of a tubular reactor for the Rh(I)/xantphos-catalysed hydroformylation, coupled in series with a K10 packed bed reactor for the aldehyde acetalization step. This pioneering strategy allowed obtaining 94 % chemoselectivity for acetal formation and 96 % regioselectivity for the linear product, resulting in a process productivity of 10.02 g product per day.