Synthesis of cyclic carbonates from diols and CO₂ catalyzed by carbenes

Abstract

The synthesis of cyclic carbonates from epoxides and CO2 is a well-established reaction, whereas the synthesis of cyclic carbonates from diols and CO2 is considerably more challenging, and few efficient catalysts are available. Here, we describe heterocyclic carbene catalysts, including one derived from a cheap and efficient thiazolium salt, for this latter reaction. The reaction proceeds at atmospheric pressure in the presence of an alkyl halide and Cs2CO3. Reaction mechanisms for the transformations involved are also proposed.

Direct Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol at Room Temperature Using Imidazolium Hydrogen Carbonate Ionic Liquid as a Recyclable Catalyst and Dehydrant

“…The yields range from 30 to 71 % (Table S1), which are better than those achieved using zinc acetate and organic bases as catalysts. The performance of [C 1 C 4 Im][HCO 3 ] is comparable to that achieved using carbenes directly . This is interesting because carbenes are expensive and unstable.…”

En route to CO2-containing renewable materials: catalytic synthesis of polycarbonates and non-isocyanate polyhydroxyurethanes derived from cyclic carbonates

“…140,141 1,2-Diols obtained from carbohydrate sources are converted to COCs using the highly toxic phosgene route or dimethyl carbonate (transesterification reaction). 142 Notably, 1,2-diols can also be converted to COCs using CO 2 as the C1 source, although this reaction is hindered by the release of water as a by-product (thermodynamic limitation, the reverse reaction is employed to generate EG from EC and water), 143,144 which leads to moderate yields and significant amounts of waste because of the water capture strategies (utilization of alkyl halides as dehydrating agents, for example). COCs can also be obtained from vegetable oils or fatty acids because they contain olefin bonds.…”

Incorporation of CO2 into carbonates through carboxylation/hydration reaction

“…Six‐membered carbonate examples are shown in Scheme . More recently, thiazolium carbene was used as a catalyst and 5‐phenyl‐1,3‐dioxan‐2‐one gave a yield of 53% in the presence of C 4 H 9 Br and Cs 2 CO 3 in work by Dyson et al …”

“…11 Six-membered carbonate examples are shown in Scheme 9. More recently, thiazolium carbene was used as a catalyst and 5-phenyl-1,3-dioxan-2-one gave a yield of 53% in the presence of C 4 H 9 Br and Cs 2 CO 3 in work by Dyson et al 37 Organocatalysts have also been studied alongside the development of metal-based catalysts. The Buchard group used available reagents including DBU, NEt 3 and TsCl, to synthesize six-membered cyclic carbonates at room temperature.…”