Use Of K2CO3 Research Articles

ChemInform Abstract: Rhodium‐Catalyzed Interconversion of Quinolinyl Ketones with Boronic Acids via C—C Bond Activation.

A rhodium-catalyzed cross-coupling of aryl and aliphatic quinolinyl ketones with boronic acids has been developed. Proceeding via quinoline-directed carbon–carbon σ bond activation, the transformation demonstrates tolerance of a range of functional groups on both the ketone and aryl boronic acid substrates, providing good to excellent yields of the new ketones, particularly those containing electron-withdrawing substituents. Catalyst reactivity is dependent on quinolinyl ketone substrates, with alkyl ketones requiring Rh(PPh3)3Cl instead of the more reactive [Rh(C2H4)2Cl]2. With the use of K2CO3 as an additive, methyl boronic acid is also a competent substrate, giving rise to an unprecedented methylation technique.

Iodine-Mediated Domino Oxidative Cyclization: One-Pot Synthesis of 1,3,4-Oxadiazoles via Oxidative Cleavage of C(sp(2))-H or C(sp)-H Bond.

An I2-promoted, metal-free domino protocol for one-pot synthesis of 1,3,4-oxadiazoles has been developed via oxidative cleavage of C(sp(2))-H or C(sp)-H bonds, followed by cyclization and deacylation. In this reaction, the use of K2CO3 as a base is found to be an essential factor in the cyclization and the C-C bond cleavage. This procedure proceeded smoothly in moderate to high yields with good functional group compatibility.

Rhodium-Catalyzed Interconversion of Quinolinyl Ketones with Boronic Acids via C-C Bond Activation.

A rhodium-catalyzed cross-coupling of aryl and aliphatic quinolinyl ketones with boronic acids has been developed. Proceeding via quinoline-directed carbon-carbon σ bond activation, the transformation demonstrates tolerance of a range of functional groups on both the ketone and aryl boronic acid substrates, providing good to excellent yields of the new ketones, particularly those containing electron-withdrawing substituents. Catalyst reactivity is dependent on quinolinyl ketone substrates, with alkyl ketones requiring Rh(PPh3)3Cl instead of the more reactive [Rh(C2H4)2Cl]2. With the use of K2CO3 as an additive, methyl boronic acid is also a competent substrate, giving rise to an unprecedented methylation technique.

Oxyalkylation of Condensed Tannin with Propylene Carbonate as an Alternative to Propylene Oxide

Propylene carbonate (PC) was used as an alternative to the hazardous propylene oxide (PO) for the oxypropylation of condensed tannins from Acacia mearnsii. The influence of the catalyst, temperature and stoichiometry was evaluated in detail. All the synthesized polymers were characterized by 1H and 31P NMR, FTIR, and size exclusion chromatography. Polyether chains were successfully grafted on all hydroxyl groups. In addition to the ether linkages, some carbonate linkages were also formed. This can cause some chain coupling reactions, through condensation and/or transesterification reactions, which ultimately increase the molar mass and reduce the OH content of the final products. The use of K2CO3 as catalyst rather than hydroxides (KOH or NaOH) and a high temperature of reaction (170 °C) were found to strongly reduce this phenomenon. Using 10–40 equiv of PC per OH in tannins, polyether/polycarbonate chains of 2–6 units in average were grafted, containing less than 25% of carbonate units. The synthesized p...

Direct Annulation of Hydrazides to 1,3,4-Oxadiazoles via Oxidative C(CO)-C(Methyl) Bond Cleavage of Methyl Ketones.

A new strategy for the synthesis of 1,3,4-oxadiazoles was established through direct annulation of hydrazides with methyl ketones. It was found that the use of K2CO3 as a base achieves an unexpected and highly efficient C-C bond cleavage. This reaction is proposed to go through oxidative cleavage of Csp(3)-H bonds, followed by cyclization and deacylation.

Palladium (0) catalyzed Suzuki cross-coupling reactions of 2,4-dibromothiophene: selectivity, characterization and biological applications

A series of novel 2-aryl1-4-bromothiophenes (2a–f), biarylthiophenes with non-identical aryl groups (3a–e) and biarylthiophenes with identical aryl groups (4a–f) were synthesized in moderate to excellent yields by using different arylboronic acids in a Suzuki–Miyaura cross-coupling reaction. The experimental results showed that the use of K2CO3 as base resulted in moderate yields compared with that of good yields obtained upon using K3PO4. The highest yield obtained using K3PO4 was 82% for 2, 4-bis (4-chlorophenyl) thiophene (4d). The synthesized compounds in the present study were examined for their biofilm inhibition and hemolysis assay. Among all compounds 2, 4-bis (4-methoxyphenyl) thiophene (4b) was found to strongly inhibit the formation of bacterial biofilm against E. coli. The compound 4b exhibited higher inhibition (80.92%) compared with the standard Rifampicin with 97.43% inhibition. The compound 2, 4-bis (4-chlorophenyl) thiophene (4d) displayed strong anti-biofilm activity with its ability to prevent the formation of Pasteurell amultocida biofilm at the percent inhibition of 74.53%. In addition, 2f showed the highest percentage hemolysis 16.0% compared with that of the standard Triton-X-100. 3

Synthesis of novel dithiocarbamyl-containing organosilicon compounds

Aldehydes-bearing dithiocarbamate moieties were generated via highly efficient and simple method based on the one-pot reaction of amines, CS2, and 4-(bromoalkoxy)benzaldehydes with the use of K2CO3 as a catalyst under solvent-free conditions. The mild reaction conditions, high yields, and broad scope of the reaction, illustrate the good synthetic utility of this method. The newly synthesized aldehydes were converted to 1,1-bis(trimethylsilyl)-1-alkenes via the Peterson olefination reaction and produced dithiocarbamate-based organosilane compounds.

Screening test for aqueous solvents used in CO2 capture: K2CO3 used with twelve different rate promoters

K2CO3 solution is widely used in the CO2-capture industry. In particular, it has advantages for treating CO2 in flue gas under high-temperature and high-pressure conditions. However, it has a lower CO2-loading capacity and slower absorption kinetics than those of amines, which are its major disadvantages. Thus, in this study, we investigated ten loading-rate promoters, five primary amines and five secondary amines, to develop higher CO2-loading capacity and faster absorption kinetics. The screening tests of the absorption and desorption processes were conducted at 70 °C and 90 °C, respectively. Based on the results, we concluded that all the amines used improved the CO2-loading and absorption kinetics compared with the use of K2CO3 alone. At a certain value CO2 loading, the respective performance of the primary and secondary amines was twice and thrice better, respectively, than the neat K2CO3 solution. Thus, secondary amines had superior absorption capacity and absorption/desorption rate compared to primary amines. Among the secondary amines, pipecolic acid, sarcosine, and isonipecotic acid were determined as the most effective absorption rate promoters.

Sequential Bicyclization to the Skeleton of Lennoxamine and Chilenine Using Pd Catalyst

Lennoxamine 1 and chilenine 2 which have an isoindolobenzazepine framework were isolated from Berberis empertrifolia Lam and Berberis darwinii Hook. Although these alkaloids have been known to show weak biological activities, their unique tetracyclic ring system has garnered much attention from synthetic chemists. In the numerous synthetic approaches, the formation of core 7and 5membered rings, actually synthesis of dehydrolennoxamine 3, has been the key target (Figure 1). In this communication we want to suggest an efficient method to the molecule, achieving the formal synthesis. Conversion of 3 to lennoxamine and chilenine has been already achieved. As most of the cyclization methods published until recently have been stepwise approaches, we wished to suggest a sequential bicyclization process from intermediate 4 in one pot. The bicyclization approach has been rare for the synthesis of 3 except radical cascade reaction to lennoxamine 1. The molecule equipped with iodine on aromatic ring, amide, alkyne functional groups was expected to undergo the desired transformation upon treating with Pd. The precursor 4 would be prepared concisely from the known compounds 5 and 6 (Scheme 1). Synthesis of 4 was carried out first by preparation of 7, reaction of 6 with NaOH/MeOH to form a benzoic acid intermediate and the following treatment with SOCl2/CH2Cl2 (48% in two steps). Coupling of 5 and 7 in the presence of TEA in CH2Cl2 afforded the requisite precursor 4 in 66% yield (Scheme 2). Bicyclization of 4 was attempted under the various conditions using palladium catalyst. In the use of K2CO3 as a base, neither Pd(OAc)2 nor other palladium catalysts such as Pd(PPh3)4, Pd(dba)2, Pd(PPh3)2Cl2 with or without ligands provided the desired compounds at all. Decomposition was detected mainly (entry 1). However, the presence of stronger base LiHMDS was found to make the reaction get started (entry 2), and among several palladium reagents, Pd(OAc)2 was the most practical and efficient. Though not much, the addition of LiCl increased the yields moderately (entries 37). The role of LiCl for the increasing the reaction yields cannot be still clearly explained. The best combination, Pd(OAc)2/LiHMDS/LiCl/DMF, was selected to afford 55% yield (entry 4). The mechanism of the transformation is suggested as follow; Oxidative addition and deprotonation to 8, which should induce the proposed bicyclization to 9, was then followed by reductive elimination to afford the desired product 3 (Figure 2). When we applied the same conditions (Table 1, entries 3 Figure 1 Scheme 1

Intermolecular Metal‐Free Cyclopropanation of Alkenes Using Tosylhydrazones

AbstractWe describe the first general method for the metal‐free cyclopropanation of alkenes by using N‐tosylhydrazones as an in situ source of diazo compounds. This new method works with a wide variety of alkenes (styrene derivatives, dienes, enynes, and electron‐deficient alkenes) by using N‐tosylhydrazones derived from various ketones or aldehydes (aromatic, aliphatic, enones). The reaction is performed with the use of K2CO3 as a base to form the diazo species and is compatible with a wide array of functional groups.

ChemInform Abstract: Copper‐Catalyzed Cross‐Coupling of Diethyl Phosphonate with Aryl Iodides.

AbstractThe use of K2CO3 as a base gives lower yields and tBu‐ONa as a base is inefficient in this reaction.

ChemInform Abstract: Copper‐Catalyzed Synthesis of 2,4‐Disubstituted Allenoates from α‐Diazoesters.

AbstractThe reaction requires the use of K2CO3 and 2 equiv.

Facile Synthesis of 1,2,3,4-Tetrasubstituted Pyrroles from Baylis-Hillman Adducts

Suitably functionalized pyrroles are the basic skeleton of many biologically important substances and numerous synthetic methods of pyrroles have been investigated extensively. However, the synthesis of pyrrole derivatives from Baylis-Hillman adducts was not developed much. Recently, we reported the synthesis of 2,3,4-trisubstituted pyrroles starting from the rearranged aza-Baylis-Hillman adducts (Scheme 1). Meantime we presumed that we could synthesize 1,2,3,4tetrasubstituted pyrrole derivatives by using the synthetic approach in Scheme 2. As shown in Scheme 2, we imagined that the reaction of Baylis-Hillman acetate 1, as the representative example, and secondary amine derivatives 2a-d could give the corresponding SN2' product 3a-d, which could be cyclized to 4a-d under basic conditions. The following acid-catalyzed dehydration and concomitant double bond isomerization of 4a-d would provide desired pyrroles 5a-d. Among the examined conditions the use of K2CO3 in CH3CN gave the best results for the preparation of 4a-d. As expected we could not observe the formation of 3 (except for 3c, entry 3 in Table 1), instead we obtained 4a-d directly in 50-74% yields as inseparable syn/anti mixtures in a one-pot reaction. Based on the H NMR spectra of 4a-d the ratio of syn/anti was 4:1 to 2:1 (footnotes b-d in Table 1), however, we did not confirm which isomer is the major one. For the reaction of 1 and 2c we isolated 3c in 34% yield (entry 3 in Table 1) together with 4c in 50% yield. For the synthesis of compound 4d (entry 4) we used 2d in slightly excess amount (footnote e in Table 1). The following dehydration step of 4a-d was carried out under the influence of p-TsOH (20-40 mol%) in benzene and we obtained the desired compounds 5a-d in 41-64% yields. Isomerization of double bond occurred during the dehydration stage simultaneously to afford pyrroles directly. The results are summarized in Table 1. However, the reaction of 1 and 2e showed somewhat different reactivity as compared with those of 2a-d (Scheme 3). When we carried out the reaction of 1 and 2e in CH3CN at room temperature the reaction did not show the formation of any new compounds in appreciable amounts presumably due to the limited solubility of 2e in CH3CN. Thus we elevated the temperature to refluxing, however, rearranged acetate was the major product in this case. After many trials we could obtain 3e in 74% yield in aqueous CH3CN at room temperature. In aqueous CH3CN the compound 2e was dissolved completely and the rearrangement of acetate group of 1 to the primary position was minimized at room temperature. With this compound 3e in our hand we prepared 4e under the same conditions of Table 1 (CH3CN,

Nonchelate and Chelate Complexes of Palladium(II) with N-Heterocyclic Carbene Ligands of Amido Functionality

The imidazolium ligand precursors [L1H1H2]Cl and [L2H12H2]Cl (H1 = NHCO, H2 = NCHN) for the potentially bidentate and pincer-type amido-NHC ligands were synthesized in 66−78% yields. Selective deprotonation of H2 in these salts with pyridine in the presence of palladium chloride resulted in the monodentate palladium(II) complexes Pd(L1H1)(py)Cl2 and Pd(L2H12)(py)Cl2. The use of K2CO3 in pyridine or DMF led to the double and triple deprotonations of the ligand precursors, giving the bis-bidentate and pincer-type palladium(II) complexes PdL12 and PdL2(py), respectively. Intriguingly, in certain cases, both the cis and the trans isomers of PdL12 were formed and isolated in pure forms. A theoretical study indicates that the trans-PdL12 is thermodynamically more stable than the cis isomer (ca. 5.8 kcal mol-1). All the new complexes are characterized by NMR (1D and 2D) and single-crystal X-ray diffraction studies. A systematic study of the new complexes in Suzuki coupling reactions revealed the following order ...

Palladium-Catalyzed Coupling of Allenylphosphonates, Phenylallenes, and Allenyl Esters: Remarkable Salt Effect and Routes to Novel Benzofurans and Isocoumarins

Coupling reactions of allenylphosphonates (OCH(2)CMe(2)CH(2)O)P(O)CH=C=CRR' [R, R' = H (1a), R = H, R' = Me (1b), R = R' = Me (1c)] with aryl iodides, iodophenol, and iodobenzoic acid in the presence of palladium(II) acetate are investigated and compared with those of phenylallenes PhCH=C=CR2 [R = H (2a), Me (2b)] and allenyl esters EtO(2)CCH=C=CR(2) [R = H (2c), Me (2d)]. While 1b and 1c couple with different stereochemical outcomes using PhI in the presence of Pd(OAc)(2)/PPh(3)/K(2)CO(3) to give phenyl-substituted 1,3-butadienes, 1a does not undergo coupling but isomerizes to the acetylene (OCH(2)CMe(2)CH(2)O)P(O)CCMe (7). In the reaction of 1c with PhI, use of K(2)CO(3) affords the butadiene (Z)-(OCH(2)CMe(2)CH(2)O)P(O)CH=C(Ph)-C(Me)=CH(2) (12); in contrast, the use of Ag(2)CO(3) leads to the allene (OCH(2)CMe(2)CH(2)O)P(O)C(Ph)=C=CMe(2) (20), showing that these bases differ very significantly in their roles. The reaction of 1a with PhI or PhB(OH)2 in (t)he presence of Pd(OAc)2/CsF/DMF leads mainly to (E)-(OCH(2)CMe(2)CH(2)O)P(O)CH=C(Me)Ph (21) and (OCH(2)CMe(2)CH(2)O)P(O)CH2-C(Ph)=CH(2) (22) and is thus a net 1,2-addition of Ph-H. Compound 1b reacts with iodophenol in the presence of Pd(OAc)(2)/PPh(3)/K(2)CO(3) to give a benzofuran that has a structure different from that obtained by using 1c under similar conditions. Treatment of 1a with iodophenol/Pd(OAc)(2)/CsF/DMF also gives a benzofuran whose structure is different from that obtained by using 2a under similar conditions. In the reaction with 2-iodobenzoic acid, 1a and 2c afford one type of isocoumarin, while 1b,c and 2a,b give a second type of isocoumarin. The structures of key compounds are established by X-ray crystallography. Utility of the phosphonate products in the Horner-Wadsworth-Emmons reaction is demonstrated.

Synthesis of Cyclopropane Derivatives Starting from the Baylis-Hillman Adducts Using Sulfur Ylide Chemistry

Cyclopropane moiety is a fundamental class of functional group that is the focus of many organic synthesis programs and performs a key structural role in a wide range of biologically active molecules. The importance of cyclopropanes is reflected in the enormous effort that has been invested in their diastereoand enantioselective synthesis. In addition, cyclopropane derivatives could be transformed to structurally diverse compounds. During the extensive studies on the chemical transformations of Baylis-Hillman adducts, we examined the introduction of cyclopropane moiety at the primary position of Baylis-Hillman adducts to form vinyl cyclopropane derivatives 2 (Scheme 1). Such vinyl cyclopropane backbone is an important entity in many naturally occurring and synthetic pyrethroidal insectides, and could be used for further chemical transformations. Our synthetic rationale is shown in Scheme 1. The starting cinnamyl bromide 1a was prepared from the Baylis-Hillman adduct and HBr according to the reported method. The reaction of 1a and dimethyl sulfide in CH3CN generated the sulfonium salt (I), which was converted into the corresponding sulfur ylide (II) by treatment with NaOH. The in situgenerated sulfur ylide (II) reacted with methyl vinyl ketone to give the desired cyclopropane derivative 2a in 45% yield as shown in Scheme 1 via the intermediate (III). The synthesis of 2a was carried out in CH3CN at room temperature within 12 h. Encouraged by the successful results we prepared other cyclopropane derivatives 2b-h and the results are summarized in Table 1. The use of Cs2CO3 instead of NaOH showed similar yield of 2a. However, the use of K2CO3 gave 2a in only trace amounts. When we used nitrogen ylide, which was made from the reaction of 1a and DABCO in the presence of NaOH, we could not observe the formation of 2a at all. Variation of the electron-withdrawing substituents (-COOMe, -COOEt, -COMe, -CN) of the starting materials 1a-f did not alter the reactivity for the formation of cyclopropanes. Ethyl vinyl ketone (entry 2) could also be used successfully as the Michael acceptor in the reaction with 1a. However, we failed to obtain the corresponding products when we replaced methyl vinyl ketone with other Michael acceptors such as methyl acrylate, acrylonitrile, and 2-cyclohexen-1one. In these cases we could not observe any major component on TLC. The reason for the failure could be explained either by the hydrolysis or low reactivity of these Michael acceptors. Fortunately, 2-chloroacrylonitrile could be used as the Michael acceptor efficiently to give 2g (entry 7) as inseparable cis-trans mixtures in 57% yield. The relative stereochemistry of the two substituents of cyclopropane was trans in all cases as reported in similar systems. We could not isolate the other stereoisomer from the reaction mixtures. Further synthetic applications of the cyclopropane products are currently underway.

Convenient Synthesis of Oxazolidinones by the Use of Halomethyloxirane, Primary Amine, and Carbonate Salt

[reaction: see text] Primary amines reacted with carbonate salts (Na2CO3, K2CO3, Cs2CO3, and Ag2CO3) and halomethyloxiranes in the presence of a base such as DBU or TEA to give oxazolidinones in high yields. The use of K2CO3 among these carbonate gave the best yield in this synthesis. A reaction mechanism was proposed that the oxazolidinone was obtained from an oxazinanone intermediate via a bicyclo[2.2.1] intermediate. The present reaction can be widely applied to convenient synthesis of useful N-substituted oxazolidinones and chiral oxazolidinones.

Potassium Carbonate, a Support for the Green Synthesis of Azoles and Diazines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Potassium carbonate, a support for the green synthesis of azoles and diazines

AbstractA novel potassium carbonate mediated synthesis of 2‐amino‐1,3‐thia/oxa zoles, 2‐amino‐1,3,4‐thia/oxa diazines and 2‐hydrazino‐1,3,4‐thiadiazines has been described here. The use of K2CO3 allows for an aqueous workup thereby eliminating the organic solvent from both the reaction step and post reaction stage, without compromising the yield and reaction time.

Solventless synthesis of thiohydantoins over K2CO3

Potassium carbonate supported solventless synthesis of thiohydantoins under microwave irradiation is described. The use of K2CO3 not only eliminates the need for external base to neutralize HCl evolved but enables aqueous work up, thus rendering the reaction procedure free of organic solvents in both the reaction step and work-up, procedure.