Co2(CO)8-induced domino reactions of ethyl diazoacetate, carbon monoxide and ferrocenylimines leading to 2-(1-ferrocenyl-methylidene)-malonic acid derivatives

Novel 2-(1-ferrocenyl-methylidene)-malonic acid derivatives are obtained upon reacting ethyl diazoacetate, carbon monoxide and ferrocenylimines in the presence of Co₂(CO)₈ as catalyst under mild conditions. Presumably, the reaction involves three steps taking place in a domino fashion, (i) carbonylation of ethyl diazoacetate leading to a ketene derivative, (ii) [2+2] cycloaddition of the ketene with the ferrocenylimine present in the reaction mixture resulting in the formation of a β-lactam and (iii) N(1)-C(4) cleavage of the β-lactam ring. In most cases, 2-(1-ferrocenyl-methylidene)-malonic acid derivatives are obtained as a separable mixture of E- and Z-isomers in ratios depending on the structure of the imine component.     

Electrogenerated cyanomethyl anion in organic synthesis: a simple diastereoselective synthesis of cis-3-alkyl-1-benzyl-4-ethoxycarbonyl-β-lactams

A ready diastereoselective synthesis of cis-3-alkyl-1-benzyl-4-ethoxycarbonyl-β-lactams has been developed by galvanostatic electrolysis of MeCN-Et₄NPF₆ solutions and subsequent addition of a N-(ethoxycarbonyl)methyl-N-benzyl-2-bromoalkylcarboxamide. The yields in β-lactams are very high and the cis isomers have been obtained in a large excess, the cis/trans ratios varying from 87/13 to 93/07.     

Synthesis of a new chiral oxazolidinone auxiliary based on d-xylose and its application to the Staudinger reaction

The synthesis of a new chiral oxazolidinone auxiliary based on d-xylose is described which is employed in diastereoselective Staudinger-type β-lactam syntheses. Using 2-chloro-1-methylpyridinium iodide as the dehydrating reagent, the reaction of auxiliary tethered acetic acid with acyclic or cyclic imines gave the desired β-lactams in good yields with excellent cis- or trans-selectivity depending on the geometry of the imine. X-Ray structure determination of one of the obtained compounds corroborated the absolute configuration for all cis products.     

Application of a chiral copper-1,1-bis{2-[(4S)-tert-butyloxazolinyl]}cyclopropane catalyst for asymmetric cyclopropanation of styrene

The structural effects of the bridge moiety and 5-position on bisoxazoline ligands were studied for the copper-catalyzed asymmetric cyclopropanation of styrene with ethyl diazoacetate. The 1,1-bis{2-[(4S)-tert-butyloxazolinyl]}cyclopropane ligand showed a remarkable enhancement in the stereoselectivities (trans/cis = 84/16, >99.9% ee for the trans product) compared with the previously reported best ligand, 2,2-bis{2-[(4S)-tert-butyloxazolinyl]}propane (trans/cis = 75/25, 99.0% ee for the trans product).     

Thiadiazole ring opening in the derivatives of 2-substituted 5-(1,2,3-thiadiazol-4-yl)-3-furoic acid under the action of bases

Transformations of the derivatives of 2-substituted 5-(1,2,3-thiadiazol-4-yl)-3-furoic acid under the action of bases has been studied. In the presence of potassium tert-butylate in THF, the studied compounds decompose with the cleavage of the thiadiazole ring, liberation of nitrogen, and formation of labile acetylene thiolates. In the presence of methyl iodide, these salts form stable 2-methylthioethynylfurans. Under the action of sodium ethylate in ethanol, thiadiazole ring of ethyl [2-methyl-5-(1,2,3-thiadiazol-4-yl)]-3-furoate is split to form the corresponding sodium acetylene thiolate. Under the action of ethanol, two molecules of this salt give bis(furyl)dithiafulvene. In the DMF–potassium carbonate system, acetylene thiolates react with primary and secondary amines giving thioamides of (4-ethoxycarbonyl-5-methylfur-2-yl)acetic acid. Treating of ethyl 2-methyland 2-N-morpholinomethyl-5-(1,2,3-thiadiazol-4-yl)-3-furoates with hydrazine hydrate leads to hydrazinolysis of the ester group and cleavage of thiadiazole ring resulting in the formation of hydrazides of 4-hydrazinocarbonylfur-2-ylacetic acid. In the case of ethyl 2-acetoxymethyl- and 2-(4-nitrophenoxy)methyl-5-(1,2,3-thiadiazol-4-yl)-3-furoates, thiadiazole ring is retained and exclusively hydrazinolysis of the ester groups is observed.     

Binuclear versus mononuclear copper complexes as catalysts for asymmetric cyclopropanation of styrene

A number of (S)-(−)-2-amino-1,1-diaryl-1-propanol compounds have been synthesized. They were used to form the binuclear copper complexes through a spontaneous assembly of the individual components, the β-aminoalcohol, 2-hydroxy-5-methyl-1,3-benzenedialdehyde, and copper acetate monohydrate, in methanol. These binuclear complexes were examined as asymmetric catalysts for cyclopropanation of styrene by ethyl diazoacetate. Moderate improvement in enantioselectivity has been observed for the binuclear versus mononuclear copper complexes. The e.e. values up to 87% for trans and 93% for cis products and the ratio between trans and cis products up to 9:1 have been obtained.     

Synthesis of β-lactams with π electron-withdrawing substituents

β-Lactams are crucial structural feature of β-lactam antibiotics and important intermediates in synthetic and pharmaceutical chemistry. Synthetic methods for β-lactams with π electron-withdrawing substituents, such as formyl (carbaldehyde), acyl, imino, carboxylic acids, carboxylates, carboxamides, cyano (carbonitriles), and nitro groups, on their 3- and/or 4-position(s) are presented in this review. The methods are divided mainly into intramolecular cyclizations, cycloaddition, and other methods, for example, Ugi-type reaction of β-keto acids, amines, and isonitriles, and modification of β-lactam derivatives. Cyclizations include cyclization of haloacetamidoacetates(malonates), intramolecular carbene insertion of α-diazoalkanamides, ring-opening cyclization of α,β-epoxyalkanamidoacetates, oxidative coupling of 3-oxoalkanamidoacetates, oxidative cyclization of N-p-hydroxyphenyl β-oxoalkanamides, intramolecular cyclization of aspartic acid derivatives or β-hydroxyalkanamides, and radical cyclization of N-vinyl β-oxoalkanamides. Cycloadditions incorporate Staudinger cycloaddition of ketenes and imines, cycloaddition of nitrones and alkynes, cycloaddition of nitrones and alkylidenecycopropanes and subsequent acidic rearrangement, and condensation of imines and enolates (ethers) of esters. The scope, limitation, and stereoselectivity are also discussed for some methods. Most of the β-lactam derivatives are key intermediates or precursors for preparation of β-lactam antibiotics and their analogs.     

Stereoselective synthesis of cis and trans-fused 3a-aryloctahydroindoles using cyclization of N-vinylic α-(methylthio)acetamides: synthesis of (−)-mesembrane

Treatment of N-(2-arylcyclohex-1-en-1-yl)-α-(methylthio)acetamides with N-chlorosuccinimide (NCS) gave 3a-aryl-2,3,3a,4,5,6-hexahydro-3-(methylthio)indol-2-ones. Desulfurization of the cyclization products followed by a catalytic hydrogenation of the resulting hexahydroindol-2-ones gave predominantly or exclusively trans-fused octahydroindol-2-ones. On the other hand, reduction of the desulfurization products with Et₃SiH in CF₃CO₂H exclusively provided cis-fused octahydroindol-2-ones. A chiral induction of N-[2-(3,4-dimethoxy)phenylcyclohex-1-en-1-yl]-α-(methylthio)acetamide having an (R)-1-(1-naphthyl)ethyl group on the nitrogen atom led to the synthesis of (−)-mesembrane and (−)-trans-mesembrane.     

Enantioselective synthesis of (1S,2S)-1,2-di-tert-butyl and (1R,2R)-1,2-di-(1-adamantyl)ethylenediamines

An enantioselective synthesis of sterically congested 1,2-di-tert-butyl and 1,2-di-(1-adamantyl)ethylenediamines has been developed. Thus, diastereomerically pure trans-1-apocamphanecarbonyl-4,5-dimethoxy-2-imidazolidinones 6 and 7 were successfully prepared by optical resolution of (±)-trans-4,5-dimethoxy-2-imidazolidinone using apocamphanecarbonyl chloride (MAC-Cl) followed by stereospecific and stepwise substitution of the dimethoxyl groups using tert-butyl or 1-adamantyl cuprates to provide (4S,5S)-4,5-di-tert-butyl and (4R,5R)-4,5-di-(1-adamantyl)-2-imidazolidinones 12 and 15, respectively. Furthermore, N-acetyl 4,5-di-tert-butyl and 4,5-di-(1-adamantyl)-2-imidazolidinones 16a,b were enantioselectively deacetylated using a catalytic oxazaborolidine system to provide enantiopure 1-p-tolylsulfonyl-4,5-di-tert-butyl-2-imidazolidinones 12 and 19 and 1-p-tolylsulfonyl-4,5-di-(1-adamantyl)-2-imidazolidinones 18 and 20, respectively. Finally, N-p-tolylsulfonyl-2-imidazolidinones 12 and 15 were treated with 30 equiv of Ba(OH)₂·8H₂O to achieve ring cleavage and to provide (1S,2S)-1,2-di-tert-butylethylenediamine 3 and (1R,2R)-1,2-di-(1-adamantyl)ethylenediamine 4.     

Synthesis of new nanocopolymer containing β-lactams

Several new monocyclic β-lactam monomers bearing the NO₂ group 2a–g were synthesized via a [2 + 2] ketene–imine cycloaddition reaction (Staudinger reaction). Calculation of coupling constant of H-3 and H-4, and the X-ray crystallography of β-lactam 2e confirmed the cis stereochemistry of these β-lactams. Then aminophenyl β-lactams were synthesized by the reduction of NO₂ to NH₂ group in the presence of Raney Ni and hydrazine hydrate. Treatment of these aminophenyl β-lactams with acryloyl chloride and sodium bicarbonate (NaHCO₃), afforded the monomers bearing the NHCOCH=CH₂ group. These acrylated β-lactam monomers were dissolved in a warm mixture of butyl acrylate and styrene and then were converted to the corresponding polyacrylate nano β-lactams by emulsion polymerization in water. A unique feature of this methodology is the ability to incorporate water-insoluble compounds directly into the nanoparticle framework. Structures of the synthesized compounds were confirmed by physical and spectral analyses. Dynamic light scattering analysis and transmission electron microscopy of the final emulsions show that the nanoparticles were about 50–70 nm in diameter.     

Synthesis and isomerization of N-α-aza-heteroaryl-β-lactams

The [2+2] carbonylative cycloaddition of N-α-aza-heteroaryl substituted imines with allyl bromide led partially to β-lactams, which underwent isomerization to the more stable α,β-unsaturated carbonyl compound. Pyrimidinone derivatives together with doubly unsaturated amides represent the remaining isolated products. The strong electron-withdrawing effect of the two α-aza-heterocycles linked to the nitrogen atom and to the C4 of the 2-azetidinone structure could give a ring expansion, through a 2-azetinone intermediate that affords the pyrimidinone compounds. The substituted amides, instead, should result from a ring-opening reaction of the β-lactam.     

Bis-β-sulfanylethylester and cyclic disulfide-S-oxides as precursors of bifunctionalized anionic derivatives with two oxidized sulfurs

The cyclic disulfide and the bis-β-sulfanyl ethyl ester derived from dithiol, N,N′-1,2-phenylenebis(3-methyl-3-sulfanylbutanamide) were used as precursors to prepare upon oxidation the cyclic disulfide-S-oxides and the thioether sulfur oxidized species including thioether/sulfoxide, bis-sulfoxide, sulfoxide/sulfone, and bis-sulfone. Ring cleavage with KOH/EtOH of the cyclic disulfide-S-monooxide followed by reaction of the opened intermediate with ethyl acrylate afforded the sulfinate/β-sulfanyl ethyl ester derivative. Selective oxidation with 1 and 2 equiv of (3S)-3-tert-butyl-3-methyl-2-(phenylsulfonyl)oxaziridine or with 3 equiv of DMD led to the isolation of a series of compounds containing a sulfonate and a β-sulfanyl, a β-sulfinyl, and a β-sulfonyl ethyl ester. Retro-Michaël reaction applied to the β-sulfonyl/β-sulfinyl and bis-β-sulfonyl derivatives enabled to produce compounds containing a sulfinate and a β-sulfinyl or a β-sulfonyl ethyl ester as well as the bis-sulfinate dianion. DMD oxidation of the latter afforded the bis-sulfonate dianion. All these anionic species were characterized by ¹H NMR, mass spectrometry, HRMS or elemental analysis. Sulfenates in such pseudopeptidic structures could not be isolated from the ring cleavage of the cyclic disulfide-S-dioxide or from a retro-Michaël reaction applied to the β-sulfinyl ethyl ester. A cyclization reaction leading to an isothiazolidin-3-one is likely to occur as observed from the ring cleavage of the cyclic disulfide-S-dioxide. Finally, Ni(II) and Co(III) have been inserted into the disulfinate dianion leading to the corresponding diamidato/disulfinato complexes S-bonded to Ni(II) or Co(III) centers.     

Stereoselective synthesis of novel C-3 functionalized 3-sulfonyl-β-lactams: Promising biologically active heterocyclic scaffolds

An efficient and operationally simple strategy for the stereoselective synthesis of novel C-3 functionalized 3-sulfonyl-β-lactam heterocycles is described. The C-3 functionalized 3-phenyl/benzylsulfonyl-β-lactams 3/3′, 5/5′ has been synthesized via Michael addition using different Michael acceptors on trans-3-phenyl/benzylsulfonyl-β-lactams 2(a–f) using K₂CO₃ as a base and acetonitrile/DMF as solvents. The reaction furnished exclusively cis-β-lactam adducts 3(a–r) using sterically less hindered Michael acceptors. Further, the effect of steric bulk and chiralilty of Michael acceptors was explored to achieve target C-3 functionalized β-lactams 3(s-u)/3′(s-u) and 5(a–c)/5′(a–c). The structural and stereochemical analysis of novel β-lactams were carried out using FT-IR, NMR (¹H, ¹³C, ¹H-¹H COSY, ¹H-¹³C COSY and ¹³C DEPT-135), elemental analysis (CHNS), mass spectrometry (EIMS and LCMS) in representative cases and single crystal X-ray crystallographic studies (3e). The cis or trans configuration of the Michael acceptor (E) at C-3 was assigned with respect to C4-H.     

Stereoselective synthesis and Lewis acid mediated functionalization of novel 3-methylthio-β-lactams

A proficient etiquette for the stereoselective synthesis of novel 3-methylthio-β-lactams and their Lewis acid mediated functionalization is described. Treatment of 2-methylthioethanoic acid and appropriate imines in the Staudinger reaction leads to the stereocontrolled synthesis of novel trans-3-methylthio-β-lactams in excellent yields. cis-3-Chloro-3-methylthio-β-lactams, obtained from stereoselective chlorination of trans-3-methylthio-β-lactams using N-chlorosuccinimide (NCS) and AIBN, were subjected to Lewis acid (TiCl₄ or SnCl₄) mediated functionalization using various active aromatic, heterocyclic and aliphatic compounds (nucleophiles). This reaction provides an easy access to novel, stereoselective cis-3-monosubstituted-3-methylthio-β-lactams, which further undergo smooth desulfurization with Raney-nickel to afford C-3 cis- and trans-monosubstituted-β-lactams. The cis or trans configuration of the hydrogen/chloro/nucleophile substituent at C-3 was assigned with respect to C4–H.     

Palladium-catalyzed synthesis of 4-alkoxycarbonyl-3,4-dihydroisoquinolin-1(2H)-ones

Palladium-catalyzed intermolecular cyclocarbonylation of diethyl (2-iodoaryl)malonates with N-tosylimines produces 4-ethoxycarbonyl-3,4-dihydroisoquinolin-1(2H)-ones in moderate to good yields. This reaction is highly stereoselective. This protocol involves Mannich addition, and subsequent cyclocarbonylation.     

2-Nitroferrocenyloxazolines: precursors to nitrofulvalenes and derivatives of (pS)- and (pR)-2-aminoferrocenecarboxylic acids

Diastereoselective lithiation of (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline, followed by addition of N₂O₄, gave (S)-2-[(_pS)-2-nitroferrocenyl]-4-(1-methylethyl)oxazoline which was subsequently converted into derivatives of (_pS)-2-aminoferrocenecarboxylic acid. The corresponding (_pR)-derivatives were obtained through use of a removable TMS blocking group. The 2-nitroferrocenyloxazolines produced in this work underwent facile photo-decomplexation to give 2-nitrocyclopentadienyliden-1,3-oxazolidenes.     

Do lipases also catalyse the ring cleavage of inactivated cyclic trans-β-lactams?

Twelve-membered cyclic cis- and trans-β-lactams 1b and 2b and the corresponding cyclic cis- and trans-β-amino acid enantiomers, 1a, 1c and 2a, 2c were prepared through the CAL-B-catalysed enantioselective ring cleavage of racemic cis-13-azabicyclo[10.2.0]tetradecan-14-one, (±)-1, and trans-13-azabicyclo[10.2.0]tetradecan-14-one, (±)-2. High enantioselectivities (E >200) were observed for the ring opening of both the cis- and trans-β-lactams when the Lipolase-catalysed reactions were performed with 0.5 equiv of H₂O in i-Pr₂O at 70 °C. The resolved β-lactams 1b and 2b (yield ⩾47%) and β-amino acids 1a and 2a (yield ⩾32%) could be easily separated.     

Synthesis of chiral β-3-amino-2-hydroxyalkanoates and 3-alkyl-3-hydroxy-β-lactams by double asymmetric induction

Reactions of chiral (2S)-enolates of dioxolan-4-ones, derived from lactic, mandelic, and phenyllactic acids, with aliphatic (S_S)- and (S_R)-tert-butylsulfinyl aldimines afforded conformationally restrained C2-disubstituted N,O-orthogonally protected 3-amino-2-hydroxyalkanoates in the form of N-sulfinyl protected 1′-aminodioxolan-4-ones. The product distribution showed that there is significant kinetic selectivity, due to the presence of ‘matched’ and ‘mismatched’ components, between the (S)- or (R)-tert-butylsulfinyl aldimines and the (2S)-enolates of the 1,3-dioxolan-4-ones. Selective methoxide-induced removal of the acetal group of the N-sulfinyl-1′-aminodioxolanones yielded the corresponding N-sulfinyl protected methyl alkanoates. In addition, the selective acid-induced removal of the sulfinyl group of the N-sulfinyl-1′-aminodioxolanones provided the corresponding N-unprotected 1′-aminodioxolanones, whose base-induced cyclization afforded the corresponding β-lactams.     

Convergent synthesis of meso-ferrocenyl porphyrins for TiO2 sensitization

Electron-donating ferrocenyl moieties have been incorporated into supramolecular carboxyporphyrin architectures Zn(II)-5-ferrocenyl-10,20-bistolyl-15-(4-methylbenzoate)porphyrin (trans-Fc-ZnP-CO₂Me), Zn(II)-5-ferrocenyl-10,15,20-tris(4-methylbenzoate)porphyrin [trans-Fc-ZnP-(CO₂Me)₃], and Zn(II)-5,15-bisferrocenyl-10,20-bis(4-benzoate)porphyrin [trans-Fc₂-ZnP-(CO₂Me)₂] for self-assembly on metal oxide nanoparticles. Efficient and economic synthesis has required a convergent strategy toward reduced symmetry trans-A₂B₂ and trans-AB₂C substitution patterns about the porphyrin macrocycle minimizing the production of porphyrin side products and increasing yields of the target ferrocenylporphyrins. Preliminary spectroscopic data in solution and in the solid state bound to mesoporous TiO₂ films are discussed.