Highly Chemoselective Catalytic Coupling of Substituted Oxetanes and Carbon Dioxide

Abstract

Abstract:The chemo--selective coupling of oxetanes and carbon dioxide to afford functional, heterocyclic organic compounds known as six--membered cyclic carbonates remains a challenging topic. Here we describe an effective method for their synthesis relying on the use of Al--catalysis. The catalytic reactions can be carried out with excellent selectivity for the cyclic carbonate product tolerating various (functional) groups present in the 2--and 3--position(s) of the oxetane ring, and the presented methodology is the first general approach towards the formation of six--membered cyclic carbonates (6MCCs) through oxetane/CO 2 coupling chemistry. Apart from a series of substituted six--membered cyclic carbonates, also the unprecedented room temperature coupling of oxetanes and CO 2 is disclosed giving, depending on the structural features of the substrate, a variety of five--and six--membered heterocyclic products. A mechanistic rationale is presented for their formation and support for the intermediary presence of a carbonic acid derivative is given. The presented functional carbonates may hold great promise as building blocks in organic synthesis and the development of new, biodegradable polymers.

Substrate‐Controlled Product Divergence: Conversion of CO2 into Heterocyclic Products

“…D;see Table 1and Table S1 in the Supporting Information) in the absence of an external nucleophile:t hese reactions conditions are related to the hydroxy oxetane conversions reported previously. [9] At 50 8 8Ca fter 14 hours we found that the aluminium-catalyst C (Table S1, entry 3) gives the highest conversion (89 %) and selectivity (> 99 %). Whereas the complex D shows higher reactivity (Table S1, entry 4; > 99 % conversion), the reaction mixture was complex, possibly resulting from polyether formation.…”

“…Recently,w ep roposed that hydroxy-and amino-substituted oxetanes can be catalytically coupled at remarkably low temperatures with CO 2 through elusive alkyl carbonic acid intermediates to afford five-or six-membered carbonates/ carbamates in the absence of external nucleophiles. [9] Further to this,o ther groups have communicated on (noncatalytic) approaches using stoichiometric additives in combination with substrates having pendent hydroxy/amine groups. [10] We envisioned that epoxy alcohols and amines would serve as ideal substrates to develop an efficient substrate-controlled catalytic approach, as these scaffolds combine high accessibility,e asy synthesis,a nd ab road molecular diversity (Scheme 1, right).…”

Catalytic One‐Pot Oxetane to Carbamate Conversions: Formal Synthesis of Drug Relevant Molecules

“…[24] Thus,t his complex was first probed in the coupling of oxetane,s everal amines and CO 2 to afford their corresponding carbamate products 1-8 ( Figure 1). These carbamates were producedi ns ynthetically useful yields of up to 91%…”

“…[21][22][23] We recently reported ar ather general method for the coupling of (functional) oxetanes and CO 2 to produce their six-membered organic carbonates. [24] In an effort to capitalize furthero nt his chemistry with the aim to prepare more complex organic molecules with potentiali np harmaceutical chemistry,w ec onsideredt hat in situ aminolysis of these carbonates could enable the construction of useful carbamates (Scheme 1). Generally, carbamates are highly interesting synthetic targets due to their wide applicationp otentiala si mportant components of polyurethane polymers, [25] agrochemicals [26] and pharmaceuticals.…”

Highly Active Salen‐Based Aluminum Catalyst for the Coupling of Carbon Dioxide with Epoxides at Ambient Temperature

“…Finding new catalyst systems for the coupling of CO 2 with epoxides to make cyclic carbonates, which have broad applications as aprotic solvents, electrolytes for lithium‐ion batteries, monomers for polymers, and pharmaceutical intermediates, is one of the most active research areas in CO 2 conversion A variety of catalyst systems have been reported for this transformation, among which nontoxic catalysts based on earth‐abundant aluminum are among the most significant . Bidentate benzotriazole phenoxides, bidentate pyrazole‐based scorpionates, bidentate 8‐hydroxyquinoline,, tetradentate triphenolateamine, tetradentate porphyrin, tetradentate salen, tetradentate salenac, salalen,, and bidentate/tridentate/tetradentate aliphatic amino alcohols, have all been used extensively as chelating ligands ...…”