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Figure 8. Mechanism that accounts for the formation of 2-oxazolidinones 8 and 9 [21]. Figure 7. L-Histidine-catalyzed cycloaddition of CO; with 1-alkyl-2-arylaziridines 7 [21].

Figure 8 Mechanism that accounts for the formation of 2-oxazolidinones 8 and 9 [21]. Figure 7. L-Histidine-catalyzed cycloaddition of CO; with 1-alkyl-2-arylaziridines 7 [21].

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In particularly, the catalytic coupling of CO, with energy- rich substrates, such as epoxides and aziridines, to generate polycarbonates/polycarbamates [8]. Among a number of feasible transformations, the atom-economic synthesis of cyclic carbamates from aziridines and CO, has been of terrific interest every industrially and academically. A variety of catalytic structures has been currently developed that efficiently promote the incorporation of this molecule into fee added chemical substances such as quinazoline- 2,4(1H,3H)-diones, azoles, 2-alkynoates, urethanes, and carbonates. Among these transformations, synthesis of 1, 3- oxazinan-2-one derivatives the use of CO, as building. As a part of my continuing critiques on chemical fixation of CO into beneficial products and new methodologies in natural synthesis [9], the usage of aziridine for their transformation into five-member heterocyclic rings such as oxazolidinonesin (Figure 1). In particular, 2-oxazolidinones are found in chiral auxiliaries (with 4-substitution) and in extraordinary antibiotics such as Linezolid and Tedizolid (with 3-aryl,5- alkyl substitution pattern), whereas aryl-fused six-membered rings are current in some HIV-battling antiretrovirals and N- methyl-D-aspartate (NMDA) receptor antagonists [10]. Conventionally, these cyclic carbamates are synthesized the use of phosgene or CO, which are hazardous and environmentally unfriendly, have been avoided, and instead, CO), was once once built-in as Cl beneficial useful resource into cyclic carbamate is formed [11].
In particularly, the catalytic coupling of CO, with energy- rich substrates, such as epoxides and aziridines, to generate polycarbonates/polycarbamates [8]. Among a number of feasible transformations, the atom-economic synthesis of cyclic carbamates from aziridines and CO, has been of terrific interest every industrially and academically. A variety of catalytic structures has been currently developed that efficiently promote the incorporation of this molecule into fee added chemical substances such as quinazoline- 2,4(1H,3H)-diones, azoles, 2-alkynoates, urethanes, and carbonates. Among these transformations, synthesis of 1, 3- oxazinan-2-one derivatives the use of CO, as building. As a part of my continuing critiques on chemical fixation of CO into beneficial products and new methodologies in natural synthesis [9], the usage of aziridine for their transformation into five-member heterocyclic rings such as oxazolidinonesin (Figure 1). In particular, 2-oxazolidinones are found in chiral auxiliaries (with 4-substitution) and in extraordinary antibiotics such as Linezolid and Tedizolid (with 3-aryl,5- alkyl substitution pattern), whereas aryl-fused six-membered rings are current in some HIV-battling antiretrovirals and N- methyl-D-aspartate (NMDA) receptor antagonists [10]. Conventionally, these cyclic carbamates are synthesized the use of phosgene or CO, which are hazardous and environmentally unfriendly, have been avoided, and instead, CO), was once once built-in as Cl beneficial useful resource into cyclic carbamate is formed [11].
normally widespread mechanism for the response of aziridine and carbon dioxide described at Figure 2 [1]. Figure 2. A simplified mechanism of the addition of CO; to aziridines [1].
normally widespread mechanism for the response of aziridine and carbon dioxide described at Figure 2 [1]. Figure 2. A simplified mechanism of the addition of CO; to aziridines [1].
Figure 3. PEG6ooo (NBu3Br)2-catalyzed fixation of CO? with 2-arylaziridines [19]. lonic liquid catalyzed synthesis of oxazolidin-2-one
Figure 3. PEG6ooo (NBu3Br)2-catalyzed fixation of CO? with 2-arylaziridines [19]. lonic liquid catalyzed synthesis of oxazolidin-2-one
Figure 4. Mechanistic proposal for the reaction [20]. (Figure 3). The cycloaddition was once carried out at room temperature for 3-12 h and afforded the favored 5-aryl-2- oxazolidinones 5 in reasonable to nearly quantitative yields. Very recently, Luo and Ji alongside with their co-workers designed and synthesized a novel imidazolium-based ionic liquid functionalized zinc porphyrin (IL-ZnTPP) as one of the most versatile catalysts known for this response [20]. In 2011, Bhanage and colleagues brought a novel polymer supported 1-(2,3-dihydroxylpropyl)-imidazolium bromide (PSDHPIMBr) catalyst for 2-oxazolidinones synthesis from CO) and aziridines under solvent-free condition. The hybrid gadget exhibited a excessive catalytic recreation and reusability for cycloaddition of 1-alkyl-2-arylaziridines 4 with CO, (5 MPa) underneath solvent-free stipulations
Figure 4. Mechanistic proposal for the reaction [20]. (Figure 3). The cycloaddition was once carried out at room temperature for 3-12 h and afforded the favored 5-aryl-2- oxazolidinones 5 in reasonable to nearly quantitative yields. Very recently, Luo and Ji alongside with their co-workers designed and synthesized a novel imidazolium-based ionic liquid functionalized zinc porphyrin (IL-ZnTPP) as one of the most versatile catalysts known for this response [20]. In 2011, Bhanage and colleagues brought a novel polymer supported 1-(2,3-dihydroxylpropyl)-imidazolium bromide (PSDHPIMBr) catalyst for 2-oxazolidinones synthesis from CO) and aziridines under solvent-free condition. The hybrid gadget exhibited a excessive catalytic recreation and reusability for cycloaddition of 1-alkyl-2-arylaziridines 4 with CO, (5 MPa) underneath solvent-free stipulations
corporations in alkyl terminal position, however N-to sylaziridines did not undergo the coupling reaction probably due to the much less nucleophilic exercise of the nitrogen. In addition, the formation of the DBN-CO, was proposed to be the intermediate of the catalytic cycle (Scheme 6) [22]. Figure 5. Synthesis of 2-oxazolidinones from CO, and aziridine catalyzed by DBN [22]. Liu’s group developed an efficient catalytic gadget the use of DBN as organocatalyst and Lil as an additive below atmospheric stress of CO, in toluene to catalyze the coupling of CO, with aziridines giving 2-oxazolidinones (Scheme 5). The system used to be tolerated by means of a quantity of N-alkyl aziridines bearing various useful
corporations in alkyl terminal position, however N-to sylaziridines did not undergo the coupling reaction probably due to the much less nucleophilic exercise of the nitrogen. In addition, the formation of the DBN-CO, was proposed to be the intermediate of the catalytic cycle (Scheme 6) [22]. Figure 5. Synthesis of 2-oxazolidinones from CO, and aziridine catalyzed by DBN [22]. Liu’s group developed an efficient catalytic gadget the use of DBN as organocatalyst and Lil as an additive below atmospheric stress of CO, in toluene to catalyze the coupling of CO, with aziridines giving 2-oxazolidinones (Scheme 5). The system used to be tolerated by means of a quantity of N-alkyl aziridines bearing various useful
Figure 6. Proposed mechanism in the synthesis of 2 -oxazolidinones from CO; and aziridinescatalyzed by DBN [22]
Figure 6. Proposed mechanism in the synthesis of 2 -oxazolidinones from CO; and aziridinescatalyzed by DBN [22]
Jiang and co-workers investigated the software of a-amino acids as hydrogen bond donor catalysts for the fixation of CO, onto aziridines. They tested quite a few naturally occurringa-amino acids for the benchmark cycloaddition of CO, (8 MPa) to N-propyl-2-phenylaziridine underneath solvent-free conditions. After optimization, it was observed
Jiang and co-workers investigated the software of a-amino acids as hydrogen bond donor catalysts for the fixation of CO, onto aziridines. They tested quite a few naturally occurringa-amino acids for the benchmark cycloaddition of CO, (8 MPa) to N-propyl-2-phenylaziridine underneath solvent-free conditions. After optimization, it was observed
Table 1. Global nucleophilicity N (eV) for the selected free NHCs and the corresponding activation free energy (kcal mot") in the ring opening steps [23]. Figure 11. Cycloaddition of CO; to several aziridines catalyzed by Nb(OEt);/TBAI [24].
Table 1. Global nucleophilicity N (eV) for the selected free NHCs and the corresponding activation free energy (kcal mot") in the ring opening steps [23]. Figure 11. Cycloaddition of CO; to several aziridines catalyzed by Nb(OEt);/TBAI [24].
Figure 9. Potential energy profile for cycloaddition of la and CO; catalyzed by NHC-CO; adduct and free NHC, respectively [23].
Figure 9. Potential energy profile for cycloaddition of la and CO; catalyzed by NHC-CO; adduct and free NHC, respectively [23].
Figure 10. The selected free NHCs in the cycloaddition of la and CO; [22]. To compare the catalytic effect between 11 and other NHCs, more free NHCs were selected to catalyze the cycloaddition response of la with CO, in the existing
Figure 10. The selected free NHCs in the cycloaddition of la and CO; [22]. To compare the catalytic effect between 11 and other NHCs, more free NHCs were selected to catalyze the cycloaddition response of la with CO, in the existing
Figure 12. Energy profile for Reaction mechanism of the cycloaddition of CO; to aziridine la catalyzed byNb(OEt);/TBAI [28]. and essential to intermediate C. The upper response barrier is ocated at 31.3 kcal/mol for the step of CO, insertion that, therefore, represents the cost figuring out step of the process [25]. This barrier is everyday with the experimentally located requirement of at least 60°C for a sizable alternatively slow conversion of the substrate. The step of ring-opening used to be decided to be 2.6 kcal/mol higher in energy than for the critical regioisomer since, electronically, the NBO value on them ethylene carbon is lower through potential of 0.182 e, for this reason less electrophilic [26, 27]. Switching to the NbCl;/TBAI system, no qualitative versions have been observed, but, quantitatively, the corresponding transition usa A — B regarded greater facile with a barrier of 6.6 clearly kcal/mol. This barrier was significantly higher for the aziridine ring opening at the methylene carbon (9.9 kcal/mol) for this purpose explaining the high-quality regioselectivity positioned for this catalyst (Table 1, Entry 7). However, the CO) insertion step grew to become much larger difficult with a barrier of 37.7 kcal/mol (thus 7.6 kcal/mol higher in strength with appreciate to the corresponding barrier for Nb(OEt);). This observation, ordinary with the difference in catalytic activity observed experimentally, suggests the importance of the steric trouble at niobium core to facilitate the insertion of CO, by favoring the Nb-N bond cleavage. Indeed, when Nb(OEt)s is used as a catalyst, this distance elongates by means of 0.128A with admire to the case of NbCl;. At the identical time the distance between the nitrogen atom and the carbon atom of CO; is 0.197A shorter for Nb(OEt);. Also for the case of NbCl;, the cooperativity via the usage of a 2" niobium atom in the step of CO, insertion was observed to be disfavored, but entirely by way of 1.3 kcal/mol. Last, the response profile was recalculated the usage of Nb(OMe);/TBAI as a catalyst to understand, and at the same time, take away the plausible noise due to the alkyl chains, which would perchance rotate freely at the experimental conditions. Apart from other minimal strength differences in the calculated pathway with admire to Nb(OEt)s, the charge identifying barrier for the step of CO, insertion increased by 2.6 kcal/mol in the case of Nb(OMe)s; the B — C transition kingdom shows a Ne ¢ °C distance that is 0.167A shorter than for the case of NbCI; but nevertheless 0.030A longer than for Nb(OEt)s. This fashion confirms the importance of the steric hassle at the niobium middle in facilitating the step of CO, insertion [28].
Figure 12. Energy profile for Reaction mechanism of the cycloaddition of CO; to aziridine la catalyzed byNb(OEt);/TBAI [28]. and essential to intermediate C. The upper response barrier is ocated at 31.3 kcal/mol for the step of CO, insertion that, therefore, represents the cost figuring out step of the process [25]. This barrier is everyday with the experimentally located requirement of at least 60°C for a sizable alternatively slow conversion of the substrate. The step of ring-opening used to be decided to be 2.6 kcal/mol higher in energy than for the critical regioisomer since, electronically, the NBO value on them ethylene carbon is lower through potential of 0.182 e, for this reason less electrophilic [26, 27]. Switching to the NbCl;/TBAI system, no qualitative versions have been observed, but, quantitatively, the corresponding transition usa A — B regarded greater facile with a barrier of 6.6 clearly kcal/mol. This barrier was significantly higher for the aziridine ring opening at the methylene carbon (9.9 kcal/mol) for this purpose explaining the high-quality regioselectivity positioned for this catalyst (Table 1, Entry 7). However, the CO) insertion step grew to become much larger difficult with a barrier of 37.7 kcal/mol (thus 7.6 kcal/mol higher in strength with appreciate to the corresponding barrier for Nb(OEt);). This observation, ordinary with the difference in catalytic activity observed experimentally, suggests the importance of the steric trouble at niobium core to facilitate the insertion of CO, by favoring the Nb-N bond cleavage. Indeed, when Nb(OEt)s is used as a catalyst, this distance elongates by means of 0.128A with admire to the case of NbCl;. At the identical time the distance between the nitrogen atom and the carbon atom of CO; is 0.197A shorter for Nb(OEt);. Also for the case of NbCl;, the cooperativity via the usage of a 2" niobium atom in the step of CO, insertion was observed to be disfavored, but entirely by way of 1.3 kcal/mol. Last, the response profile was recalculated the usage of Nb(OMe);/TBAI as a catalyst to understand, and at the same time, take away the plausible noise due to the alkyl chains, which would perchance rotate freely at the experimental conditions. Apart from other minimal strength differences in the calculated pathway with admire to Nb(OEt)s, the charge identifying barrier for the step of CO, insertion increased by 2.6 kcal/mol in the case of Nb(OMe)s; the B — C transition kingdom shows a Ne ¢ °C distance that is 0.167A shorter than for the case of NbCI; but nevertheless 0.030A longer than for Nb(OEt)s. This fashion confirms the importance of the steric hassle at the niobium middle in facilitating the step of CO, insertion [28].
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