Subsequent Ring Closure Reactions Research Articles

Gallatabenzene Ligands Emerging from Open Lutetocene and Yttrocene Methyl Complexes.

Utilizing ternary mixtures [LnMe3]n/K(2,4-dtbp)/GaMe3 (Ln=Lu, Y; 2,4-dtbp=2,4-di-tert-butyl-pentadienyl), a series of metallacycles is accessible via tandem salt metathesis/deprotonation. Depending on the precursor molar ratio, both gallatabenzene and lutetacyclic moieties with fully planar metallacycles are obtained, which were further analyzed using DFT calculations. The precursor molar ratio affects the extent of pentadienyl C-H-bond activation and oligomerization to tetra- and pentametallic arrays. Reacting a 1 : 2 : 2 mixture at -40 °C gave the open sandwich methyl complex (2,4-dtbp)2Lu(CH3), displaying a vital intermediate for subsequent ring-closure reactions.

Synthesis of dithienofurans via cascade copper catalysed dual C-S coupling and ring closure reactions under mild conditions.

We have developed a mild catalytic approach for the synthesis of new dithienofuran derivatives via cascade copper catalysed dual C–S coupling and subsequent ring closure reactions. Sonogashira coupling between perbromofuran and terminal alkynes produced 3,4-dibromo-2,5-dialkynylfuran (1) in good yields. Next, copper catalysed C–S coupling between 1 and Na2S·9H2O and a subsequent ring-closure reaction afforded dithienofuran compounds (2) under mild conditions. We found that this strategy shows broad substrate scope and can be used to prepare not only aryl and heteroaryl but also alkyl substituted dithienofuran derivatives in up to 70% yields. Furthermore, we proposed a mechanism including two catalytic cycles: a typical Cu(i)/Cu(iii) catalytic cycle and a subsequent Cu(ii) induced cyclization mechanism.

ChemInform Abstract: Novel Route to Triethylsilyl‐Substituted Cyclopropanes.

AbstractRadical addition of vinyl compounds (II) to xanthates gives addition products of type (III) which are converted to the corresponding cyclopropanes by ozonolysis and subsequent ring closure reaction.

Benzoxazine containing polyester thermosets with improved adhesion and flexibility

AbstractHigh molecular weight polyesters containing thermally curable benzoxazine units in the main chain have been synthesized. For this purpose, first the diol functional monomer is synthesized through the Mannich and subsequent ring closure reactions of bisphenol‐A, paraformaldehyde, and 5‐amino‐1‐pentanol. Polycondensation of the resulting benzoxazine and pyromellitic dianhydride or 4‐4′‐(hexafluoroisopropylidene) diphatalic anhydride with or without dibutyltin laurate yielded the corresponding polyesters with the molecular weights between 5800 and 7000 Da. The structures of the precursor diol monomer and the resulting polyesters are confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy analysis. Curing behavior of both the monomer and polymers has also been studied by differential scanning calorimetry. Flexible films of the polyesters were obtained by solvent casting on tin plates and crosslinked by heating in the absence of any catalyst. The cured films exhibited high flexibility and adhesion on the tin plates as determined by ASTM and DIN tests. Thermal properties of the cured polymers were also investigated by thermogravimetric analysis (TGA). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4279–4284, 2010

Photoinduced ring opening reactions and subsequent thermal ring closure reactions in the thymine—ammonia system and related systems

The photo-induced ring opening reactions of thymine (Thy) and 1-methylthymine (MeT) with ammonia and with methylamine (MA) at basic pH, and the subsequent ring closure reactions of the resulting adducts, have been studied. In the photo-induced reaction of Thy with ammonia, the dominant product is the E form of N-carbamoyl-3-amino-2-methylacrylamide (IIIa). Heating or acid treatment of aqueous IIIa results in rapid formation of Thy as final product, while allowing IIIa to stand at 4 degrees C produces Thy and two isomeric Thy hydrates, namely trans- and cis-6-hydroxy-5,6-dihydrothymine (Ia and IIa). The main products in the other reactions have analogous structures and undergo analogous ring closure reactions. Incubation of IIIa (and similar adducts) in phosphate buffer near pH 7 significantly enhances the rate of hydrate formation; other weak acid/conjugate base buffer systems also increase the rate of hydrate formation. A mechanism leading from opened ring adduct (e.g.IIIa) to hydrates (e.g.Ia and IIa) is proposed; ring closure leads initially to a dihydrothymine intermediate containing a 6-amino moiety, while further reaction with water produces the observed hydrates. The results described may be relevant to understanding the fate of cross-links generated by photo-induced reaction of thymine moieties in DNA with lysine residues in nuclear proteins (e.g. histones) when they are formed in a cellular environment. Decomposition of such cross-links, catalyzed by cellular phosphate, could lead to production of thymine hydrates attached to lysine residues contained in the protein partner and concurrent generation of an apyrimidinic site in the DNA partner.

Photoinduced transformation of matrix-isolated methyl 2-pyrone-3-carboxylate into methyl 2-pyrone-5-carboxylate via intramolecular hydrogen shift in open-ring aldehyde–ketene

Photochemical transformations of methyl 2-pyrone-3-carboxylate ( mp3c) were studied by matrix-isolation technique. The dominating primary photoreaction induced by UV ( λ > 295 nm) light was α-bond cleavage leading to open-ring aldehyde–ketene. Another reaction characteristic of α-pyrones, isomerisation to the Dewar form, did not occur for mp3c. The ring-opening photoreaction was followed by intramolecular hydrogen shift and subsequent ring-closure reaction converting the aldehyde–ketene into methyl 2-pyrone-5-carboxylate ( mp5c). Upon prolonged UV irradiation, mp3c completely transformed into mp5c and its Dewar isomer Dmp5c. Unequivocal identification of mp5c and Dmp5c photoproducts was enabled by exact knowledge of their experimental IR spectra, recorded in separate experiments.

Ultrafast dynamics of photoinduced ring-opening and the subsequent ring-closure reactions of spirooxazines in crystalline state

We investigated photoisomerization dynamics of spironaphthooxazine (SNO) and its chloro-substituted derivative (Cl–SNO) in crystalline phase by femtosecond diffuse reflectance absorption spectroscopy. Although the photoinduced ring-opening reaction occurred in 3 ps and <1 ps for SNO and Cl–SNO, respectively, photoisomerization to trans-planar photomerocyanine did not take place. The generated non-planar open form of SNO lived for 2 ns, while that of Cl–SNO returned to the spiro form in 1 ps. The crystalline phase results are compared to the analogous experiments in amorphous solids with a view of restricted conformational changes of molecules embedded in a crystal lattice.

Reactions of cisplatin hydrolytes with methionine, cysteine, and plasma ultrafiltrate studied by a combination of HPLC and NMR techniques

The reactions of cis-[PtCl(NH 3) 2(H 2O)] + with l-methionine have been studied by 1D 195Pt and 15N NMR, and by 2D[ 1H, 15N] NMR. When the platinum complex is in excess, the initial product, cis-[PtCl(NH 3) 2(Hmet- S)] + undergoes slow ring closure to [Pt(NH 3) 2(Hmet- N,S)] 2+. Slow ammine loss then occurs to give the isomer of [PtCl(NH 3)(Hmet- N,S)] + with chloride trans to sulfur. When methionine is in excess, a reaction sequence is proposed in which trans-[PtCl(NH 3)(Hmet- S) 2] + isomerises to the cis-isomer, with subsequent ring closure reactions leading to cis-[Pt(Hmet- N, S) 2] 2+. Near pH 7, methionine is unreactive toward cis-[PtCl(OH)(NH 3) 2]. By contrast, l -cysteine reacts readily with cis-[PtCl(OH)(NH 3) 2] at pH 7, but there were many reaction products, including bridged species. Cis-[PtCl(OH)(NH 3) 2] reacts with reduced thiols in ultrafiltered plasma but these are oxidized if the plasma is not fresh or appropriately stored. With very low concentrations of the platinum complexes (35.5 μM), HPLC experiments (UV detection at 305 nm) indicate that the thiolate (probably cysteine) reactions become simpler as bridging becomes less important.

Diastereoselective Synthesis of a Bis(tetrahydroindenyl)zirconocene Dichloride with “Ansa-Fused” Annulated Six-Membered Ring Systems: A Specific Solution of the Synthetic rac-/meso-Group 4 Bent Metallocene Problem

1-Phenyl-1,4-pentanedione (3) is selectively converted to the corresponding fulvene−ketone (4) by treatment with cyclopentadiene in the presence of pyrrolidine. Treatment with lithium dimethylcuprate results in selective CH3-addition at the fulvene carbon and subsequent ring-closure reaction to give 7, which in the presence of lithium diisopropylamide is rapidly dehydrated to yield the bicyclic fulvene 8. Its treatment with amalgamated calcium metal leads to reductive fulvene coupling and formation of the calcocene complex (10) of the substituted 7,7‘-bi(tetrahydroindenyl) ligand. Only the respective rac-isomer is obtained. Hydrolysis of 10 followed by double deprotonation with butyllithium yields the corresponding 7,7‘-bi(tetrahydroindenyl) dianion equivalent 16. In tetrahydrofuran, 16 is cleaved at the 7,7‘-linkage with formation of the “monomeric” disproportionation products 11-Li and 12-Li, and treatment of 16 with zirconium tetrachloride in THF leads back to the formation of the fulvene 8. Transmetal...

ChemInform Abstract: Photochemistry of Some Extended π‐Systems: Type A and Aryl Rearrangements of Systems with Extended Conjugation Related to Cyclohexadienones and Cyclohexenones. Mechanistic and Exploratory Organic Photochemistry.

AbstractFormylation of the diphenylcyclohexenone (I) with ethyl formate (II) and subsequent ring closure reaction with methyl vinyl ketone (IV) yield the diphenyltetrahydronaphthalenone (V) after treatment with a base.

Functionalized chloroenamines in aminocyclopropane synthesis III. synthesis and assignment of configuration of two isomeric morpholinobicyclo[3.1.0]hexane derivatives

Reaction of the acylated chloroenamine 7 with cyanide gave the endo-morpholino compound 11. The endo-morpholino configuration of 11 was established by subsequent ring closure reactions generating tricyclic derivatives 14, 16 and 17. LiAlH 4 reduction of 11 afforded aminoalcohol 12. The corresponding exo-morpholino isomer 20 could be obtained by LiAlH 4 reduction of exo-morpholino compound 19 which was accessible from N-tosylcarbamoylated chloroenamine 10 and cyanide. ΔGX values of 75.4–77.6 kJ/mol and 52.1 kJ/mol were determined for the morpholine dynamics in the two isomeric compounds 12 and 20, respectively. This demonstrates that 1H NMR spectroscopic determination of the dynamics of morpholine allows an assignment of the configuration even in the case of twofold substituted morpholinobicyclo[n.1.0]alkane derivatives.

Metal-ion-controlled transamination in the synthesis of macrocyclic Schiff-base ligands. Part 2. Stepwise synthesis, ring expansion/contraction, and the crystal and molecular structure of a ten-co-ordinate barium(II) complex

Reaction of 2,6-diacetylpyridine with diethylenetriamine in the presence of salts of the alkaline-earth metal ions Mg2+–-Ba2+ in methanol at room temperature yields complexes of the open-chain Schiff-base ligand L1 derived from the condensation of one molecule of 2,6-diacetylpyridine with two molecules of diethylenetriamine. The use of higher reaction temperatures affords complexes (MgII excepted) of a macrocyclic ligand L2 derived from the [2 + 2] condensation of two molecules of diketone with two molecules of diprimary amine, provided the amine is not present in excess. The intermediacy of the L1 complexes in the L2 macrocycle formation is demonstrated by their subsequent ring-closure reactions both in the presence and absence of added diketone. A transamination mechanism is suggested for the ring closures in the absence of diketone. Crystals of [BaL2(ClO4)2] aremonoclinic with a= 19.427(12), b= 9.320(8), c= 9.768(11)A, β= 116.1(1)°, Z= 2, and space group P21/a. 4 420 Reflections above background have been measured by diffractometer of which 2 312 were used in refinement to R 0.075. The macrocycle L2 contains an 18-membered inner large ring and not the expected 24-membered ring L3. The smaller (di-imine) ring may be considered as being derived from the larger (tetraimine) ring by nucleophilic addition of the two secondary amine groups across adjacent azomethine bonds with accompanying expulsion of two imidazolidine rings from the inner large ring. The Ba2+ ion is ten-co-ordinate being bonded to six nitrogens of the inner large ring in approximately planar array [Ba–N 2.841 (7)–-2.891 (8)A] and to four oxygen atoms of two perchlorate groups [Ba–O 2.923(10), 3.060(11)A]. The single co-ordinated alkaline-earth metal ion in the L2 complexes may be replaced by two copper(II) or two silver(I) ions with accompanying expansion of the macrocycle to the 24-membered (tetraimine) form L3. The reversibility of the L2⇌ L3 ring expansion/contraction has been established.

ChemInform Abstract: THE REACTION OF ETHYL 4‐BROMO‐2‐ETHOXYCARBONYL‐2‐PENTENOATE WITH SOME NUCLEOPHILES

AbstractDie Titelverbindung (IV) reagiert mit den angegebenen Nucleophilen zu den Substitutionsderivaten (V) und (VI).

Preparation and alkylation of substituted β-hydroxydithiocinnamic acids

A number of substituted β-hydroxydithiocinnamic acids have been prepared. By use of so-called ion-pair extraction technique a general method has been found for the preparation of β-hydroxydithiocinnamic esters in high yields. From these esters both symmetrical and unsymmetrical ketene mercaptals have been synthesized, and in some cases thio-Claisen rearrangement and subsequent ring-closure reactions have been observed.