Reactions of 5-mercaptoazoles and pyridine-2-thiones with acetylenic esters. Selectivity of the formation of novel fused thiazin-4-ones and thiazolidin-4-ones

A systematic study of the reactions of dimethyl acetylenedicarboxylate (DMAD) and methyl propynoate with 5-mercaptoazoles and pyridine-2-thiones has been carried out and as a result, a number of novel imidazo[1,5-b]thiazin-4-ones 6a,b, pyrazolo[1,5-b] thiazin-4-ones 15a-f, imidazo[1,5-b]thiazol-4-ones 7a,b and thiazolo[3,2-a]pyridines 21a-c have been prepared. The influence of the size of the ring of the starting "cyclic" thioamides on the size of the fused ring in the reaction products has been established. The preferred formation of a six-membered thiazine ring took place in the reactions of 5-mercaptoazoles. In contrast, the five membered thiazolidine ring is formed in reactions of pyridine-2-thiones. In both cases the product is a five-membered ring fused to a six-membered heterocycle.     

Intramolecular carbolithiation reactions of chiral alpha-amino-organolithium species

Enantiomerically enriched alpha-amino-organolithium species, in which the lithium atom is attached to a stereogenic carbon centre, have been found to be chemically stable at room temperature in a solvent of very low polarity and undergo intramolecular carbolithiation onto an unactivated alkene. The configurational stability of the chiral organolithium species, bearing a variety of N-alkenyl substituents, was probed by studying the enantiomeric purity of the cyclization products. With N-but-3-enyl-2-lithiopyrrolidine, cyclization to the five-membered ring is more rapid than racemization and a high yield of the pyrrolizidine alkaloid (+)-pseudoheliotridane was obtained with no loss of optical purity. In contrast, with N-pent-4-enyl-2-lithiopyrrolidine, cyclization to the six-membered ring was found to occur with significant loss of optical purity. The cyclization to the six-membered ring was determined to occur with a half-life, t(1/2) approximately 90 min at 23 degrees C. The epimerization of this organolithium species in hexane/Et2O 4:1 was calculated to have a half-life, t(1/2) approximately 30 min at 23 degrees C. Enhanced levels of enantioselectivity for the formation of the indolizidine ring system were obtained using an alkene bearing a terminal phenylthio substituent. With N-[(3-phenylthio)-prop-2-enyl]-2-lithiopyrrolidine, cyclization to the four-membered ring occurs with poor enantioselectivity at low temperature in THF but is highly enantioselective at room temperature in a solvent of very low polarity.     

Investigation of the halocyclization of S- and N-allyl derivatives of 2-benzothiazolethione

3-Allyl-2-benzothiazolethione reacts with iodine regiospecifically with annelation of the five-membered ring, while with bromine a mixture of the five- and six-membered rings are formed. 2-Allylthioben- zothiazole reacts with halogens with annelation of the five- and six-membered rings, while 2-(2-methyl-2-propenyl)thiobenzothiazole is annelated at the five-membered ring.     

Alkylierung der 3-Acyl-thio- und -dithio-carbazinester-Gruppierung ?CO?NH?NH?CS?YR

3-Benzoyl-thiocarbazic acid O-methyl ester 7a and 3-benzoyl-dithiocarbazic acid methyl ester 7b are methylated, in presence of alkali, at the SH group of 1a , the ene-thiol tautomer of 1 , to give the 3-benzoyl-isothiocarbazic acid O, S-dimethyl ester 8a and the 3-benzoyl-isodithiocarbazic acid dimethyl ester 8b resp., which clearly differ from the N-methylated compounds 11a and 12a or 11b and 12b prepared from the two N-methyl benzohydrazides 9 and 10 resp. (melting points, thin-layer chromatography and NMR. spectra). The previously reported [1] ring closure of 3-(ω-chloroalkanoyl)-thiocarbazic acid O-alkyl esters and -dithiocarbazic acid alkyl esters can be interpretated as an intramolecular auto-alkylation of ? CO? NH? NH? CS? YR: the 3-(chloroacetyl)-compounds 2 are S-alkylated (enethiol form) to the six-membered thiadiazinones 4 , but the 3-(3-chloropropionyl)-compounds 3 are N-alkylated to the pyrazolidinones 6 , the five-membered ring being preferred in the latter case to the seven-membered ring 5 which would be formed by S-alkylation. Hence the position of alkylating attack depends on the size of the ring to be formed. As a consequence, starting from 3-(4-chlorobutyryl) compounds 13 , an alternative between the two N-alkylation products 14 (five-membered ring) and 15 (six-membered ring) would be expected. On the contrary however, a combination of 1,3,4-thiadiazole ring closure and chlorine elimination predominates, giving the 5-(3-hydroxypropyl)-1,3,4-thiadiazoles 16 . This reaction may proceed via the butyrolactone intermediates 18 and could therefore be interpreted as O-alkylation followed by rearrangement.     

Stereoselective formation of fused tricyclic amines from acyclic aldehydes by a cascade process involving condensation, cyclization, and dipolar cycloaddition

The preparation of tricyclic amines from acyclic precursors is described using a cascade of tandem reactions involving condensation of an aldehyde with a primary amine, cyclization (with displacement of a halide), and then in situ deprotonation or decarboxylation to give an azomethine ylide or nitrone followed by intramolecular dipolar cycloaddition. The methodology is straightforward, and the aldehyde precursors are prepared easily and quickly in high yield using nitrile alkylations followed by DIBAL-H reduction. The relative ease of reaction of various substrates with different tether lengths between the aldehyde and the halide or dipolarophile has been studied. Several primary amines including simple amino acids such as glycine, alanine, and phenylalanine and derivatives such as glycine ethyl ester and also hydroxylamine have been investigated. High yields are obtained in the formation of different tricyclic ring sizes; the dipolar cycloaddition necessarily creates a five-membered ring, and we have investigated the formation of five- and six-membered rings for the other two new ring sizes. In all cases, yields are high (except when using glycine when the tether to the terminal alkene dipolarophile leads to a six-membered ring), and most efficient is the formation of the tricyclic product in which all five-membered rings are formed. Examples with an alkyne as the dipolarophile were also successful. In all the reactions studied, the products are formed with complete regioselectivity and remarkably with complete stereoselectivity. The key step involves the formation of three new rings and potentially up to four new stereocenters in a single transformation. The power of the chemistry was demonstrated by the synthesis of the core ring systems of the alkaloids (+/-)-scandine and (+/-)-myrioneurinol and the total syntheses of the alkaloids (+/-)-aspidospermine, (+/-)-quebrachamine, and (+/-)-aspidospermidine.     

Synthesis of 5-(7-hydroxyhept-3-enyl)-1,2-dithiolan-3-one 1-oxide, a core functionality of antibiotic leinamycin

5-(7-Hydroxyhept-3-enyl)-1,2-dithiolan-3-one 1-oxide 1 possessing both the 1,2-dithiolan-3-one 1-oxide five-membered ring and the double bond at the gamma position of the heterocycle, characteristic of the antibiotic leinamycin, was synthesized. In addition, the activated ester form of 1 was prepared that may be useful for coupling 1 to certain DNA-binding agents.     

N,N′-二[3-氯-5S-(l-孟氧基)-2(5H)-4-呋喃酮基]-1,4-丁二胺的合成及晶体结构(英文)

合成了N,N′-二[3-氯-5S-(l-孟氧基)-2(5H)-4-呋喃酮基]-1,4-丁二胺,并通过IR,1H NMR,MS和X射线单晶衍射对其进行了表征.X射线单晶衍射结果表明:标题化合物的不对称结构单元中包含一个平面的呋喃酮环和一个椅式的环己烷环,四个手性中心.标题化合物通过N—H…O分子间氢键作用实现空间堆积.     

Chemistry of the aromatic 9-germafluorenyl dianion and some related silicon and carbon species

Dipotassio-9-germafluorenyl dianion (3b) was synthesized by reduction of 9,9-dichloro-9-germafluorene (4b) with sodium/potassium alloy in tetrahydrofuran. The X-ray crystal structure of 3b, like that for the analogous silicon compound 3a, shows C-C bond length equalization in the five-membered metallole rings and C-C bond length alternation in the six-membered benzenoid rings, indicating aromatic delocalization of electrons into the germole ring of 3b. Calculated nucleus independent chemical shift (NICS) values indicate that the five-membered ring is more aromatic than the six-membered rings in 3a and 3b. Derivatization of 3b with Me(3)SiCl gave 9,9-bis(trimethylsilyl)-9-germafluorene (5). Controlled oxidation of 3b yielded dipotassio-9,9'-digerma-9,9'-bifluorenyl dianion (6). Reaction of 6 with MeOH yielded 9,9'-digerma-9,9'-bifluorene (7). The X-ray structure of 6 indicates C-C bond length alternation in the five-membered rings. Thus dianion 6, like its silicon analogue 8, has the negative charges localized at metal atoms and no aromatic character. Dipotassio-9,9'-bifluorenyl dianion (9), the carbon analogue of 6, exhibits aromaticity with its X-ray crystal structure showing the C-C bond length equalization in both the five- and six-membered rings. Derivatization of 9 with MeI gave 9,9'-dimethyl-9,9'-bifluorene (10). The structure of 10 shows that the two fluorenyl rings are cis to each other with a torsional angle of 59 degrees and a long C-C single bond (1.60 A) connecting them.     

Intramolecular sulfur-ylide additions to ketones. A cyclopentane annulation1

Various 2-(3′-phenylthiopropyl)cycloalkanones were prepared from the corresponding cyclic ketones and subjected to S-alkylation by triethyloxonium tetrafluoroborate followed by potassium $\text{tert}$-butoxide treatment to give bicyclic epoxides with new five-membered carbocycles. A related cyclization to a six-membered ring was also observed.     

Cu(I)-catalyzed intramolecular C-C coupling of activated methylene compounds with vinyl halides: efficient synthesis of functionalized alkylidenecyclobutanes

With the catalysis of CuI/L-proline, a number of 2-(3-bromobut-3-enyl)malonates underwent efficient intramolecular C-vinylation leading to the synthesis of functionalized alkylidenecyclobutanes. Competition experiments revealed that this four-membered ring closure is fundamentally preferred over the corresponding five-membered ring closure.     

N，N’-二[3-氯-5S-（l-孟氧基）-2（5H）-4-呋喃酮基]-1，4-丁二胺的合成及晶体结构

合成了N,N’-二[3-氯-5S-（l-孟氧基）-2（5H）-4-呋喃酮基]-1,4-丁二胺,并通过IR,^1H NMR,MS和X射线单晶衍射对其进行了表征．X射线单晶衍射结果表明：标题化合物的不对称结构单元中包含一个平面的呋喃酮环和一个椅式的环己烷环,四个手性中心．标题化合物通过N—H…O分子间氢键作用实现空间堆积．     

Square planar complexes of nickel(II), palladium(II) and platinum(II) with 1-(2-hydroxyphenyl)-3,5-diphenylformazan

Summary A novel series of formazan complexes of general formula FoML [H₂Fo = 1-(2-hydroxyphenyl)-3,5-diphenylformazan; M = Ni^II, Pd^II or Pt^II; L = NH₃, py and Ph₃P] are described. The formazan nickel(II) system shows linkage isomerism; one isomer, A, contains an unusual five-membered formazan chelate ring, whereas the other, isomer B, has the usual six-membered ring.¹³C n.m.r., u.v. and i.r. spectra are presented and interpreted. From these the palladium and platinum complexes appear to contain the six-membered ring of the B type isomer.     

Intrinsic gas-phase electrophilic reactivity of cyclic N-alkyl- and N-acyliminium ions

The intrinsic gas-phase reactivity of cyclic N-alkyl- and N-acyliminium ions toward addition of allyltrimethylsilane (ATMS) has been compared using MS(2) and MS(3) pentaquadrupole mass spectrometric experiments. An order of electrophilic reactivity has been derived and found to agree with orders of overall reactivity in solution. The prototype five-membered ring N-alkyliminium ion 1a and its N-CH(3) analogue 1b, as well as their six-membered ring analogues 1c and 1d, lack N-acyl activation and they are, accordingly, inert toward ATMS addition. The five- and six-membered ring N-acyliminium ions with N-COCH(3) exocycclic groups, 3a and 3b, respectively, are also not very reactive. The N-acyliminium ions 2a and 2c, with s-trans locked endocyclic N-carbonyl groups, are the most reactive followed closely by 3c and 3d with exocyclic (and unlocked) N-CO(2)CH(3) groups. The five-membered ring N-acyliminium ions are more reactive than their six-membered ring analogues, that is: 2a > 2c and 3c > 3d. In contrast with the high reactivity of 2a, its N-CH(3) analogue 2b is inert toward ATMS addition. For the first time, the transient intermediates of a Mannich-type condensation reaction were isolated-the beta-silyl cations formed by ATMS addition to N-acyliminium ions-and their intrinsic gas-phase behavior toward dissociation and reaction with a nucleophile investigated. When collisionally activated, the beta-silyl cations dissociate preferentially by Grob fragmentation, that is, by retro-addition. With pyridine, they react competitively and to variable extents by proton transfer and by trimethylsilylium ion abstraction-the final and key step postulated for alpha-amidoalkylation. Becke3LYP/6-311G(d,p) reaction energetics, charge densities on the electrophilic C-2 site, and AM1 LUMO energies have been used to rationalize the order of intrinsic gas-phase electrophilic reactivity of cyclic iminium and N-acyliminium ions.     

Six- versus five-membered ring formation in radical cyclizations of 7-bromo-substituted hexahydroindolinones

[reaction: see text] Radical cyclization of N-allyl-7-bromo-3a-methyl-hexahydroindol-2-one affords a six-membered ring product that prevails over the isomeric five-membered compound. The former product is generated through two reaction pathways: (a) 6-endo-trig ring closure and (b) rearrangement of an intermediate methylenecyclopentyl radical obtained by 5-exo-trig cyclization.     

The Driving Force for the Acylation of β-Lactam Antibiotics by L,D-Transpeptidase 2: Quantum Mechanics/Molecular Mechanics (QM/MM) Study

β-lactam antibiotics, which are used to treat infectious diseases, are currently the most widely used class of antibiotics. This study focused on the chemical reactivity of five- and six-membered ring systems attached to the β-lactam ring. The ring strain energy (RSE), force constant (FC) of amide (C−N), acylation transition states and second-order perturbation stabilization energies of 13 basic structural units of β-lactam derivatives were computed using the M06-2X and G3/B3LYP multistep method. In the ring strain calculations, an isodesmic reaction scheme was used to obtain the total energies. RSE is relatively greater in the five-(1a–2c) compared to the six-membered ring systems except for 4b, which gives a RSE that is comparable to five-membered ring lactams. These variations were also observed in the calculated inter-atomic amide bond distances (C−N), which is why the six-membered ring lactams C−N bond are more rigid than those with five-membered ring lactams. The calculated ΔG^# values from the acylation reaction of the lactams (involving the S−H group of the cysteine active residue from L,D transpeptidase 2) revealed a faster rate of C−N cleavage in the five-membered ring lactams especially in the 1–2 derivatives (17.58 kcal mol⁻¹). This observation is also reflected in the calculated amide bond force constant (1.26 mDyn/A) indicating a weaker bond strength, suggesting that electronic factors (electron delocalization) play more of a role on reactivity of the β-lactam ring, than ring strain.     

Hydroformylation of high polymers

A new class of polymeric materials has been prepared and subjected to preliminary evaluation. These materials were obtained by hydroformylation of diene-based polymers. The olefinic bonds were saturated and aldehyde groups attached. The extent of reaction may be varied at will up to 100% double bond conversion. The properties of these polymers are dominated by the active aldehyde groups. One of the chief characteristics of simple aldehydes is their ability to polymerize forming mainly aldehyde trimers and tetramers. This same phenomenon has been shown to occur with polymeric aldehydes with consequent gel formation. The gelling tendency has been closely related to the aldehyde content per unit volume which may be conveniently varied by (1) the concentration of the initial polymer, (2) the degree of unsaturation in the polymer, and (3) the extent of double bond conversion. Any combination which gives a free aldehyde concentration in excess of 1 × 10^?4 mole/ml. is very prone to gel. The loose gels can be readily reversed by conditions which depolymerize aldehydes. The propensity of the aldehyde polymers to crosslink upon evaporation of the solvent was used to form films. These films were not discolored by ultraviolet light but under such treatment became quite brittle. The products may be stabilized by conversion of the aldehyde groups to more stable derivative, in particular the acetal. The extent of acetal formation has been shown to be controlled by steric factors. Complete polyacetal formation was possible only when the aldehyde groups were well dispersed along the polymer chain. Certain aldehyde derivatives (acetals, oximes) are thermoplastic. They soften at lower temperature than commercial plastics.     

Synthesis, structure, and electrochemical properties of a family of 2-(arylazo)phenolate complexes of ruthenium with unusual C-C coupling and N=N cleavage

Reaction of 2-(4'-R-phenylazo)-4-methylphenols (R = OCH3, CH3, H, Cl, and NO2) with [Ru(dmso)(4)Cl2]affords a family of five ruthenium(III) complexes, containing a 2-(arylazo)phenolate ligand forming a six-membered chelate ring and a tetradentate ligand formed from two 2-(arylazo)phenols via an unusual C-C coupling linking the two ortho carbons of the phenyl rings in the arylazo fragment. A similar reaction with 2-(2'-methylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl2] has afforded a similar complex, in which one 2-(2'-methylphenylazo)-4-methylphenolate ligand is coordinated forming a six-membered chelate ring, and the other two ligands have undergone the C-C coupling reaction, and the coupled species is coordinated as a tetradentate ligand forming a five-membered N,O-chelate ring, a nine-membered N,N-chelate ring, and another five-membered chelate ring. Reaction of 2-(2',6'-dimethylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl2] has afforded a complex in which two 2-(2',6'-dimethylphenylazo)-4-methylphenols are coordinated as bidentate N,O-donors forming five- and six-membered chelate rings, while the third one has undergone cleavage across the N=N bond, and the phenolate fragment, thus generated, remains coordinated to the metal center in the iminosemiquinonate form. Structures of four selected complexes have been determined by X-ray crystallography. The first six complexes are one-electron paramagnetic and show rhombic ESR spectra. The last complex is diamagnetic and shows characteristic 1H NMR signals. All the complexes show intense charge-transfer transitions in the visible region and a Ru(III)-Ru(IV) oxidation on the positive side of SCE and a Ru(III)-Ru(II) reduction on the negative side.     

13C-NMR-spektren von bicyclo[n.1.0]alkenen

The ¹³C-NMR spectra of some bicyclo[3.1.0]hex-3-en-2-ols and of some bicyclo[3.1.0]hex-3-en-2-ones are described. The bond parameters of bicyclo[3.1.0]hex-3-en-2-one are derived from a structure determination of endo-6-methoxy-1,3,6-triphenylbicyclo[3.1.0]hex-3-en-2-one. The electron density is calculated by the EHT method, and correlated with the ¹³C NMR shifts. For comparison the ¹³C NMR spectrum of a bicyclo[4.1.0]hepta-1,5-dione derivative is analysed. The influence of a cyclopropane system attached to a five-membered and to a six-membered ring is elucidated. Whereas the five-membered ring shows conjugation between the carbonyl group and the cyclopropane system, the same effect is not observed in the six-membered ring analogue. This is explained by the highly rigid structure of the five-membered ring.     

Dual-activation protocol for tandem cross-aldol condensation: An easy and highly efficient synthesis of α,α′-bis(aryl/alkylmethylidene)ketones

Commercially available lithium hydroxide monohydrate (LiOH·H₂O) was found to be a novel ‘dual activation’ catalyst for tandem cross-aldol condensation between cyclic/acyclic ketones and aromatic/heteroaromatic/styryl/alkyl aldehydes leading to an efficient and easy synthesis of α,α′-bis(aryl/alkylmethylidene)ketones at r.t. in short times. The reaction of aryl, heteroaryl, styryl and alkyl aldehydes with acyclic and five/six-membered cyclic ketones afforded excellent yields after 2 min to 1.25 h. The reaction conditions were compatible with various electron withdrawing and electron donating substituents, e.g. Cl, F, NO₂, OMe and NMe₂. The rate of the cross-aldol condensation was influenced by the nature of the ketone and electronic and steric factors associated with the aldehyde. The reaction took place at a faster rate for acyclic ketone (e.g., acetone) than that for cyclic ketone (e.g., cyclohexanone). In case of cycloalkanones, the rate of the reaction was dependent on the size of the ring of the cycloalkanone. The cross-aldol condensation of cyclopentanone was faster than that of cyclohexanone for a common aldehyde. In case of reactions involving aliphatic aldehyde having α-hydrogen atom no self-aldol condensation of the aldehyde took place.     

A DFT study of model complexes of zinc hydrolases and their inhibition by hydroxamic acids

DFT calculations carried out on zinc acetate and zinc hydroxamates using the Hartree-Fock and B3LYP methods with the 6-311+G basis set give a series of stable pseudotetrahedral chelates (ZnL(2)) (L = OAc, FA, AA, NMeAA, GA, SA). Addition of a water molecule to these chelates gives the hydrates, ZnL(2).H(2)O, which in all cases are energetically more stable than the corresponding chelate. Hydrates formed from O,O coordinated hydroxamate species with a five-membered chelate ring contain water molecules occupying vacant coordination sites of the zinc atom. In contrast, those formed from zinc chelates with four-membered chelate rings contain a water molecule inserted into the chelate ring to give a six-membered ring in which one hydrogen of the water molecule is H-bonded to an oxygen atom of the zinc chelate with the water oxygen strongly bonded to the zinc. A slight lengthening of the H-bonded O-H bond suggests incipient hydroxide activation of water by zinc. In contrast, the O,O bonded hydroxamates do not incorporate water into the chelate ring nor activate the water in accordance with the ability of hydroxamic acids to inhibit zinc containing metalloenzymes.