Ewoud

The front cover picture depicts bio-based bis-vinyl ether structures which were synthesized through a catalytic transfer vinylation reaction, where a cationic iridium complex was used as the catalyst, sodium acetate as the base, vinyl acetate as the vinylating agent, and 2-MeTHF as a green solvent. Many of the herein described (bis)-vinyl ethers are reported for the first time and bear high potential as an integral part in adhesives, coatings, or UV-inks. Details can be found in the research article by de Vries and co-workers (B. Spiegelberg, H. Jiao, R. Grauke, C. Kubis, A. Spannenberg, A. Brandt, A. Taden, H. Beck, S. Tin, J. G. de Vries, Adv. Synth. Catal. 2022, 364, 1251–1263; DOI: 10.1002/adsc.202101348).

Easy, unexpected access to useful 2-substituted succinates was achieved starting from various allyl derivatives, including allyl carbonates, under mild conditions. The selectivity of this Pd-catalyzed oxidative Bis-Alkoxycarbonylation is governed by the combined effect of the ligand (anthryl α-diimine) and the nucleophile (benzyl alcohol). Mechanistic insights, based on DFT calculations, were proposed.

Abstract

A chemoselective method for the carbonylation of allylic substrates CH₂=CHCH₂X (X=OAc, OC(O)CH₂CN, OPh, OEt, OC(O)OPh, OC(O)OiBu, N(H)C(O)Ph, N(Ph)C(O)Ph, N(H)Boc, N(Ph)Boc, Ph, CO₂Bn, CN), leading to alkyl succinates with preservation of the X group, under Pd(II)-catalyzed oxidative carbonylation conditions, has been developed. Our method shows a completely different inverse chemoselectivity with respect to the “classical” substitutive carbonylation of the allyl compounds, which is known to provide β,γ-unsaturated carbonyl derivatives through the formation of a π-allylpalladium intermediate. An accurate study, carried out using allyl acetate as model substrate, allowed to maximize the selectivity in the envisioned 2-CH₂X substituted succinates. The best catalyst is generated in situ by mixing Pd(TFA)₂ (TFA=trifluoroacetate) and the N,N′-di(anthracen-9-yl)butane-2,3-diimine ligand. p-Benzoquinone was used as oxidant in presence of benzyl alcohol, which acts as a nucleophile and as a solvent, under 4 bar of CO at 20 °C. A combined effect of the ligand and the nucleophile, rationalized through DFT calculations, has been observed both in promoting the bis-alkoxycarbonylation process and in preventing π-allylpalladium-mediated side reactions, allowing the attainment of succinate derivatives with moderate to good yields.

Nature Catalysis, Published online: 03 March 2022; doi:10.1038/s41929-022-00751-0

Nature Communications, Published online: 03 February 2022; doi:10.1038/s41467-022-28285-w

Abstract

The iridium catalyzed transfer vinylation of bio-based polyols and of other alcohols and phenols with interesting structural motifs was accomplished with vinyl acetate in 2-MeTHF as a green solvent. The optimized synthetic procedure has as main advantages the use of catalytic instead of stoichiometric amounts of base and high selectivities towards the formation of bis-vinyl ethers as a result of the suppression of the acetal formation reaction that typically occurs in the vinylation of diols. In addition, the thermodynamically preferred transesterification reaction leading to the acetate esters and bis-esters was completely suppressed. DFT calculations revealed an iridium-acetate complex as the active catalytic species and they disclosed the importance of the carbonyl group of vinyl acetate for the formation of a six-membered cyclic intermediate.

A new synthetic route towards benzimidazo[2,1-b]quinazolin-12-ones has been developed, which relies on the Pd-catalyzed intramolecular aminocarbonylation of N-(2-bromophenyl)-1H-benzimidazol-2-amines. Using near stoichiometric amounts of ¹³CO, isotopically labelled benzimidazo[2,1-b]quinazolin-12-ones were synthesized.

Abstract

A carbonylative route towards the synthesis of benzimidazo[2,1-b]quinazolin-12-ones was developed. The key step in this strategy consists of an intramolecular carbonylative lactam formation, starting from N-(2-bromophenyl)-1H-benzimidazol-2-amines. These precursor molecules were synthesized by two different methods to introduce a variety of substituents on the aromatic ring systems. Interestingly, only near-stoichiometric amounts of carbon monoxide were required in the ring-closing aminocarbonylation reaction, rendering the developed strategy also suitable for late-stage ¹³C-isotopic labelling.

No noble metal needed: The cobalt-catalysed reductive etherification of aldehydes with alcohols under syngas conditions has been investigated and proved to be efficient for a broad range of coupling partners. The promoting effect of phosphine oxides allows for a milder and more general reaction: the methodology presented a good functional group tolerance and could be applied to natural alcohols.

Abstract

A phosphine-oxide-promoted, cobalt-catalysed reductive etherification using syngas as a reductant is reported. This novel methodology was successfully used to prepare a broad range of unsymmetrical ethers from various aldehydes and alcohols containing diverse functional groups, and was scaled-up to multigram scale under comparably mild conditions. Mechanistic experiments support an acetalization–hydrogenation sequence.

A dual catalysis strategy via carboxylate species featuring weak nucleophilicity and basicity is used for the direct carbonylative polymerization of various epoxides for the production of original advanced polyhydroxyalkanoates (PHAs) with high molecular weight and tunable functionalization. This study represents a rare example of PHAs synthesis using epoxides and carbon monoxide as raw materials.

Abstract

Polyhydroxyalkanoates (PHAs) are a unique class of commercially manufactured biodegradable polyesters with properties suitable for partially substituting petroleum-based plastics. However, high costs and low volumes of production have restricted their application as commodity materials. In this study, tri-metallic complexes were developed for carbonylative polymerization via a dual catalysis strategy, and 17 products of novel PHAs with up to 38.2 kg mol⁻¹ M _n values were discovered. The polymerization proceeds in a sequential fashion, which entails the carbonylative ring expansion of epoxide to β-lactone and its subsequent ring-opening polymerization that occurs selectively at the O-alkyl bond via carboxylate species. The wide availability and structural diversity of epoxide monomers provide PHAs with various structures, excellent functionalities, and tunable properties. This study represents a rare example of the preparation of PHAs using epoxides and carbon monoxide as raw materials.