Abstract:A detailed mechanistic investigation of epoxide carbonylation by the catalyst [(salph)Al(THF)2]+ [Co(CO)4]- (1, salph = N,N'-o-phenylenebis(3,5-di-tert-butylsalicylideneimine), THF = tetrahydrofuran) is reported. When the carbonylation of 1,2-epoxybutane (EB) to beta-valerolactone is performed in 1,2-dimethoxyethane solution, the reaction rate is independent of the epoxide concentration and the carbon monoxide pressure but first order in 1. The rate of lactone formation varies considerably in different solvent… Show more
“…Additionally, the mechanism for epoxide carbonylation by [Lewis acid] + [Co(CO) 4 ] − was proposed: (1) epoxide activation by the [Lewis acid] + , (2) attack by Co(CO) 4 − to form a ring-opened intermediate, (3) CO insertion into Co-alkyl bond, and (4) ring-closure, which results in β-lactone formation (Fig. 1) 22,23 . Although these catalysts are highly efficient, their application is limited because of the difficulties associated with their separation and reuse.Figure 1Schematic depiction of proposed mechanism for epoxide carbonylation by [Lewis acid] + [Co(CO) 4 ] − .…”
The synthesis of β-lactones from epoxides through ring-expanding carbonylation using homogeneous catalysts has received much attention. However, homogeneous catalysts suffer from difficulty in product separation and recycling of the catalyst, limiting their industrial usage. Herein, a novel heterogeneous catalyst, [Cr-metalated porous porphyrin polymer]+[Co(CO)4]−, was prepared and used for the conversion of propylene oxide (PO) to β-butyrolactone; this catalyst presented superior catalytic activity and selectivity (99%) than our previous heterogeneous catalyst. In addition, the catalyst was readily separated from the product without significant loss of catalytic activity. A possible method to recover the original catalytic activity also was demonstrated.
“…Additionally, the mechanism for epoxide carbonylation by [Lewis acid] + [Co(CO) 4 ] − was proposed: (1) epoxide activation by the [Lewis acid] + , (2) attack by Co(CO) 4 − to form a ring-opened intermediate, (3) CO insertion into Co-alkyl bond, and (4) ring-closure, which results in β-lactone formation (Fig. 1) 22,23 . Although these catalysts are highly efficient, their application is limited because of the difficulties associated with their separation and reuse.Figure 1Schematic depiction of proposed mechanism for epoxide carbonylation by [Lewis acid] + [Co(CO) 4 ] − .…”
The synthesis of β-lactones from epoxides through ring-expanding carbonylation using homogeneous catalysts has received much attention. However, homogeneous catalysts suffer from difficulty in product separation and recycling of the catalyst, limiting their industrial usage. Herein, a novel heterogeneous catalyst, [Cr-metalated porous porphyrin polymer]+[Co(CO)4]−, was prepared and used for the conversion of propylene oxide (PO) to β-butyrolactone; this catalyst presented superior catalytic activity and selectivity (99%) than our previous heterogeneous catalyst. In addition, the catalyst was readily separated from the product without significant loss of catalytic activity. A possible method to recover the original catalytic activity also was demonstrated.
“…In this regard, heterometallic catalysts containing Al-salen cations and [Co(CO) 4 ] − anions have been studied for carbonylation of epoxides (to yield anyhydrides). 58,59 Clearly, there is scope for preparing other systems for cooperative catalysis employing Al as a metal centre. In addition to Al, other heavier p-block metals have recently found use in carbon dioxide utilization.…”
“…[123][124] The reaction is initiated by dissociation of a weakly bound ligand from aluminium to generate Lewis acidic complex I. Activation of the epoxide (II) is followed by nucleophilic attack of cobalt to give five-coordinated aluminium alkoxide complex III. Insertion of CO into the C-Co bond then gives intermediate IV, which reacts with CO to give complex V. The subsequent four-membered ring formation from V to give VI has been proposed to be rate-limiting, and the intermediacy of V was supported by IR spectroscopy and kinetic studies.…”
In this section, the synthesis of saturated N-and O-heterocycles via formal cycloaddition is presented. The main focus is on metal-catalyzed reactions involving C-C or C-X bond cleavage in three-or four-membered rings. After a fast presentation of pioneering works, the important breakthroughs of the last two decades are presented. The section starts with reactions involving three-membered rings. Formal [3+2] cycloadditions of donor-acceptor-substituted cyclopropanes and methylenecyclopropanes with carbonyls and imines are important methods to access tetrahydrofuran and pyrrolidine heterocycles. Formal [3+3] cycloadditions have emerged more recently. On the other hand, reactions of epoxides and aziridines with carbon monoxide or cumulenes are now well-established method to access heterocycles. These processes have been completed more recently with cycloaddition with olefins, carbonyls and imines. The section ends with the emerging field of four-membered ring activation for cycloaddition with systems. This is the peer reviewed version of the following article: Top. Heterocycl. Chem. 2013, 32, 225, which The discovery of classical cycloaddition reactions, such as the (hetero) DielsAlder and 1,3-dipolar cycloadditions, has contributed tremendously to a more efficient access towards both carbocycles and heterocycles. The introduction of the term cycloaddition was necessary to distinguish these new types of reactions from previously discovered processes leading to cyclic structures, such as the famous Robinson annulation. In principle, each cycloaddition can be considered as a special case of the more general annulation process, but from which point on an annulation can be called a cycloaddition has been the topic of intensive discussions for decades, and is still not settled today. In 1968, Huisgen proposed a set of rules for the definition of cycloaddition, and the two first are still largely recognized as prerequisite: Although the rule that all the atoms of the starting materials have to be included in the product is not explicitly included in the definition, this requirement is usually recognized by most organic chemists. Even if electrocyclic cyclization processes were included in the original definition of Huisgen, the term cycloaddition is mostly used today for those reactions proceeding via the formation of at least two new bonds. Nevertheless, several researchers think that the term cycloaddition should be more strictly limited to reactions involving a continuous overlap of electrons, and consequently allowing a concerted process. In fact, in his seminal publication, Huisgen already introduced further rules, in particular rule number 3, which explicitly stated that cycloadditions should not involve the cleavage of sigma bonds: -Huisgen Rule 3: "Cycloadditions do not involve the cleavage of bonds." Unfortunately, in the same publication, Huisgen also described several reactions proceeding via -bond cleavage as cycloaddition. To solve this definition dilemma, several researchers have used th...
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