A novel ring-opening based tandem domino process of an activated vinyl cyclopropane

An activated vinyl cyclopropane reacted with substituted benzaldehydes to afford α-methylene γ-butyrolactones in the presence of DABCO·6H₂O. This tandem domino process took place in aqueous media, and was presumably initiated with the ring opening of cyclopropane by the nucleophilic addition of DABCO·6H₂O.     

β-Stannylpropionaldehyde. A versatile cyclopropane building-block

Various functional group-substituted cyclopropanes were prepared in good yield starting from β-tributylstannylproprionaldehyde via homoallylstannanes or γ-hydroxypropylstannanes.     

Nitrile anion cyclization with epoxysilanes followed by Brook rearrangement/ring-opening of cyclopropane nitriles/alkylation

[reactions: see text] The reaction of delta-silyl-gamma,delta-epoxypentanenitrile derivatives 9-12 with a base and an alkylating agent affords (Z)-delta-siloxy-gamma,delta-unsaturated pentanenitrile derivatives via a tandem process that involves the formation of a cyclopropane derivative by epoxy nitrile cyclization followed by Brook rearrangement and an anion-induced cleavage of the cyclopropane ring. Exclusive formation of a (Z)-derivative from trans-epoxides is explained by the reaction pathway that involves a backside displacement of the epoxide by the alpha-nitrile carbanion and the O-Si bond formation followed by concerted processes involving Brook rearrangement and the anti-mode of eliminative ring fission of the cyclopropane from the rotamer 19. The fact that (E)-isomers are exclusively obtained from cis-epoxides and alpha-cyclopropyl-alpha-silylcarbinol derivative 26 provides experimental support for the proposed pathway.     

One-step synthesis of heteroaromatic-fused pyrrolidines via cyclopropane ring-opening reaction: application to the PKCbeta inhibitor JTT-010

A ring-opening reaction of cyclopropanes with five-membered heteroaromatics having a leaving group at C(2) was found to provide heteroaromatic-fused pyrrolidines in one step. This reaction was successfully applied to the synthesis of the protein kinase C-beta inhibitor JTT-010, which possesses a dihydropyrrolo[1,2-a]indole core.     

Synthesis of biomimetic light-driven molecular switches via a cyclopropyl ring-opening/nitrilium ion ring-closing tandem reaction

A cyclopropyl ring-opening/nitrilium ion ring-closing tandem reaction has been conveniently used in an expeditious synthetic approach to light-driven Z/E molecular switches featuring an imine function conjugated to olefin groups that mimics natural protonated Schiff bases.     

A biomimetic approach to dihydrobenzofuran synthesis.

A method for an acid-catalyzed construction of dihydrobenzofuran heterocycles (14) from 2-(2'-hydroxyethyl)quinone precursors 10 is presented. The putative oxonium ion intermediate 17 formed by an intramolecular hydroxyl cyclization followed by dehydration is reduced in situ by an added dihydroquinone source. Good to excellent yields of cyclized products are realized in all cases except for highly electron deficient systems, and these suffer reduction prior to oxonium ion formation. All products are monomeric and derived from a two-electron transfer except for 10 g, which affords the dimeric dihydrobenzofuran. The amount of cyclization or reduction product is governed by the HOMO/LUMO gap between the quinone substrate and the dihydroquinone additive, and the product distribution can be adjusted by modifying the electronic properties of the added reducing agent.     

Stereospecific peptide folds. A rationally designed molecular bracelet

A canonical planar beta-hairpin peptide, stereochemically reengineered into a semicircular bracelet type motif by L-to-D stereochemical inversion in two pairs of its cross-strand neighbor residues, displays protein like ordering including two-state behavior in H2O, which is unusual for a small peptide of this size.     

A kinetic study of the ring-opening process in tungsten carbonyl complexes containing hemilabile metallodithiolate ligands

The synthesis of the metallodithiolate derivative of tungsten pentacarbonyl from the reaction of photogenerated W(CO)(5)THF and Ni-1 ((1,5-bis(2-mercapto-2-methylpropane)-1,5-diazacyclooctanato)nickel(II)) is described, along with its crystal structure. In N,N-dimethylformamide solution, the pentacarbonyl exists in equilibrium with its tetracarbonyl analogue and carbon monoxide. The pentacarbonyl complex stereoselectively loses cis carbonyl ligands, as is apparent from (13)CO-labeling studies, where the thus-formed tetracarbonyl tungsten complex resulting from chelate ring-closure is preferentially (13)CO-labeled among the two mutually trans CO groups. The kinetics of the addition of CO to the tetracarbonyl to afford the metal pentacarbonyl were monitored by means of in situ infrared spectroscopy in the nu(CO) region at CO pressures between 28 and 97 bar and temperatures over the range 45-60 degrees C. Under these conditions, there was no evidence for W-S bond cleavage in the pentacarbonyl complex with concomitant formation of W(CO)(6). These studies reveal that the tetracarbonyl complex and CO are only slightly unstable with respect to the formation of the pentacarbonyl complex, with an equilibrium constant at 50 degrees C of about 2.8 M(-1) or DeltaG degrees = -1.4 kJ/mol. The activation parameters determined for the ring-opening process (DeltaH = 89.1 kJ/mol and DeltaS = -37.2 J/mol.K) suggest a solvent-assisted concerted ring-opening mechanism.     

Tandem cyclopropane ring-opening/Conia-ene reactions of 2-alkynyl indoles: a [3 + 3] annulative route to tetrahydrocarbazoles

A Zn(NTf(2))(2) catalyzed tandem reaction consisting of a nucelophilic ring opening of 1,1-cyclopropanediesters by 2-alkynyl indoles followed by a Conia-ene ring closure results in the efficient one-step synthesis of tetrahydrocarbazoles. The adducts may be further elaborated to carbazoles.     

Stereospecific total synthesis of somocystinamide A

The first total synthesis of somocystinamide A, a disulfide dimer with extremely labile enamide functional groups, was accomplished in a concise and stereospecific manner. Somocystinamide A is reported to possess exceptionally potent antiangiogenic and tumoricidal activities. The current work should enable further pharmacological investigation of this important natural product.     

A biomimetic synthesis of chrysanthemol

The factors governing the competitiun between 1,2-and 1,3-eliminations have been studied and the results obtained have been applied to a biomimetic synthesis of chrysanthemol.     

钩吻素一子的仿生合成

我们以天然老刺木碱(3)为原料,成功地完成了钩吻素-子(1)的仿生合成.这一结果不仅进一步证实了钩吻素-子的结构,还揭示出钩吻素-子与另一钩吻生物碱钩吻素-戊(2)以及3之间可能的生源关系.     

A biomimetic synthesis of lucidene

Lucidene has been shown to be derived from alpha-humulene and o-benzoquinone methide generated under thermal conditions.     

Continuous crystalline carbonate apatite thin films. A biomimetic approach.

In contrast to extensive studies on hydroxyapatite thin films, very little has been reported on the thin films of carbonated apatite (dahllite). In this report, we describe the synthesis and characterization of a highly crystalline dahllite thin film assembled via a biomimetic pathway. A free-standing continuous precursor film of carbonated calcium phosphate in an amorphous phase was first prepared by a solution-inhibited templating method (template-inhibition) at an air-water interface. A stearic acid surface monolayer acted as the template, while a carbonate-phosphate solution composed a binary inhibition system. The precursor film formed at the air/water interface was heated at 900 degrees C and transformed into a dense crystalline film that retained the overall shape of the precursor. The crystalline phase was characterized by XRD and IR to be a single-phase carbonate apatite, with carbonate substitutions in both type A (OH-) and type B (PO4(3-)) lattice positions.     

Probing the bent bonds in cyclopropane systems for gas storage and separation process: A computational study

The hydrogen, carbon dioxide, and carbon monoxide gas adsorption and storage capacity of lithium-decorated cyclopropane ring systems were examined with quantum chemical calculations at density functional theory, DFT M06-2X functional using 6-31G(d) and cc-pVDZ basis sets. To examine the reliability of M06-2X DFT functional, a few representative systems are also examined with complete basis set CBS-QB3 method and CCSD-aug-cc-pVTZ level of theory. The cyclopropane systems can bind to one Li⁺ ion; however, the corresponding the methylated systems can bind with two Li⁺ ions. The cyclopropane systems can adsorb six hydrogen molecules with an average binding energy of 3.8 kcal/mol. The binding free energy (ΔG) values suggest that the hydrogen adsorption process is feasible at 273.15 K. The calculation of desorption energies indicates the recyclable property of gas adsorbed complexes. The same number of CO₂ and CO gas molecules can also be adsorbed with an average binding energy of −14.4 kcal/mol and −10.7 kcal/mol, respectively. The carbon dioxide showed ~3–4 kcal/mol better binding energy as compared to carbon monoxide and hence such designed systems can function as a potential candidate for the separation of these flue gas molecules. The nature of interactions in complexes was examined with atoms in molecules analysis revealed the electrostatic nature for the interaction of Li⁺ ion with cyclopropane rings. The chemical hardness and electrophilicity calculations showed that the gas adsorbed complexes are rigid and therefore robust as gas storage materials.     

A Stereospecific Approach to cis-anti-cis Triquinanes

Abstract

A methodology for the synthesis of compounds containing the cis-anti-cis fused triquinane system has been developed starting from tricyclo[5.2.1.0^2,6]deca-4,8-dien-3-(exo)ol 6 involving Ireland ester Claisen rearrangement and intramolecular diazo ketone cyclopropanation reactions as key steps.