Selective catalytic synthesis of 1,2- and 8,9-cyclic limonene carbonates as versatile building blocks for novel hydroxyurethanes

The selective catalytic synthesis of limonene-derived monofunctional cyclic carbonates and their subsequent functionalization via thiol-ene addition and amine ring opening is reported. A phosphotungstate polyoxometalate catalyst used for limonene epoxidation in 1,2 position is shown to also be active in cyclic carbonate synthesis, allowing a two-step-one-pot synthesis without intermittent epoxide isolation. When used in conjunction with a classical halide catalyst, the polyoxometalate increased the rate of carbonation in a synergistic double-activation of both substrates. The cis isomer is shown to be responsible for incomplete conversion and by-product formation in commercial mixtures of 1,2-limomene oxide. Carbonation of 8,9-limonene epoxide furnished the 8,9-limonene carbonate for the first time. Both cyclic carbonates underwent thiol-ene addition reactions to yield linked bis-carbonates which can be used in linear non-isocyanate polyurethanes synthesis as shown by their facile ring-opening with N-hexylamine. Thus, the selective catalytic route to monofunctional limonene carbonates demonstrated gives straightforward access to monomers for novel bio-based polymers.