A Catalytic Domino Approach toward Oxo-Alkyl Carbonates and Polycarbonates from CO₂, Propargylic Alcohols, and (Mono- and Di-)Alcohols

Abstract

We have explored the domino reaction between propargylic alcohols, carbon dioxide, and various alcohols with the double objective to prepare oxo-alkyl carbonates with a high yield and selectivity under mild conditions and to extend the process to the synthesis of phosgene-free polycarbonates. We first searched for a common catalytic system that was highly selective for the two reactions involved in the domino process, i.e., the cycloaddition of CO 2 to propargylic alcohol to yield α-alkylidene cyclic carbonate (αCC) and the alcoholysis of αCC to furnish oxo-alkyl carbonate. Kinetics studies monitored by operando IR spectroscopy and supported by 1 H NMR analyses and DFT modeling have permitted us to identify an efficient binary catalytic system composed of a combination of tetrabutylammonium phenolate [TBA][OPh] and silver iodide (AgI) (or copper iodide (CuI)) and to understand its action mode. The [TBA][OPh]/ AgI catalytic system (5 mol %) was then successfully implemented for the selective preparation of a range of oxo-alkyl carbonates by the domino reaction with alcohols and propargylic alcohols of different structures. Most of these oxo-alkyl carbonates were produced at a high yield (≥97%) under mild operating conditions, i.e., at 60 °C and 1 bar of CO 2 . The one-pot synthesis of various poly(βoxo-carbonate)s from bis(propargylic alcohol)s, diols, and CO 2 was finally investigated, and the best operating conditions ([TBA][OPh]/AgI (10 mol %), 60 °C, 15 bar) afforded polycarbonate oligomers with weight-average molar masses of 4300 g/mol.Although the system should be optimized to produce longer polymer chains, this process offers a new phosgene-free alternative to the synthesis of functional polycarbonates poly(β-oxo-carbonate)s) under mild conditions.

Perspectives for the Upgrading of Bio‐Based Vicinal Diols within the Developing European Bioeconomy

“…Regarding precursors of α‐alkylidene cyclic carbonates such as 63 , some propargylic alcohol derivatives can be obtained from acetylene and formaldehyde. Moreover, these propargylic precursors are quite tunable, therefore offering a broad range of cyclic carbonates structures, with a huge potential in applications related to polymer or organic chemistries [175] …”

“…Intermediate alcoholysis consisted in the nucleophilic attack of a diol alkoxide, yielding an enol species which tautomerizes into a ketone, and thus, to catalyst recycling (Scheme 39). [175] The fast rearrangement of the enol intermediate into a more stable tautomer ketone is seen as the driving force of the reaction [183] . In the last step (Scheme 39), the desired carbonate and the α‐hydroxyketone byproduct 68 are generated through intramolecular cyclization of ketone intermediate [22] …”

“…Compound 63 is often seen as the prototype of the α‐alkylidene cyclic carbonate family of compounds. One of the major hurdles of this strategy is ascribed to the large formation of wastes and low atom economy arising from the use of a coupling agent, [151] as well as its typical petro‐based nature and complex purifications [175,176] . Though, green road toward the manufacturing of 12 already exists at laboratory scale, via the epoxidation of 1,2‐propanediol ( 33 ) directly synthesized from GL [177] .…”

En Route to CO2-Based (a)Cyclic Carbonates and Polycarbonates from Alcohols Substrates by Direct and Indirect Approaches

“…The key to the success lies in the utilization of a single dual system, i.e., tetrabutylammonium phenolate/AgI, capable of catalyzing two different reactions, i.e., the carboxylative cyclization of CO2 with the bispropargylic alcohol to deliver the bis(αalkylidene cyclic carbonates) in situ, followed by its polymerization in cascade with a primary diol. Even though the results were promising, only oligomers with Mn values in the range of 1000 to 2700 g/mol were obtained due to the occurrence of side reactions [220]. Taking advantage of this concept, new CO 2 -based bis(α-alkylidene cyclic carbonates) were designed by our group.…”

“…Bis(α-alkylidene cyclic carbonates) were either prepared by direct coupling of bis-propagylic alcohols with CO 2 (aliphatic spacer R 2 , see Scheme 33) or by heck coupling of two CO 2 -based exovinylene cyclic carbonates with 1,4-diiodobenzene (aromatic spacer R 2 , see Scheme 33). These new monomers were further copolymerized via step growth with diols to obtain regioregular PCs with microstructures free of any defects [108,[219][220][221]. Indeed, unlike conventional 5-membered cyclic carbonates, the formation of ether linkages (via decarboxylation) was not observed.…”