Novel reaction pathways for 2-pyridone [4+4] photoadducts

[Structure: see text] Transannular ring closure of a pyridone-furan [4+4] photoadduct has been evaluated in a model system. A combination of nitrogen substitution and an isopropyl group gave full control of the four new stereogenic centers. Chlorination transformed the 1,5-cyclooctadiene to a [4.2.0] ring system instead of to the expected [3.3.0] ring system. Changing an alkene to an enone suppressed this pathway and led to a new rearrangement, converting the 5-8-5 ring system to a 6-7-5 system.     

Synthesis of one‐, two‐ and three‐ring macrocyclic,bifunctional compounds for use in radiolabelling monoclonal antibodies

The synthesis of new linked bis‐ and tris‐ring tetraazamacrocyclic (bifunctional) reagents for use in an alternative strategy for radiolabelling antibodies is described. For comparison with the above systems, a new single ring bifunctional system incorporating a dioxocyclam ring is also reported.     

Total Synthesis of Codeine

In this paper, a new strategy towards the synthesis of codeine and morphine is reported. This new approach features a cascade cyclization to construct the dihydrofuran ring, and an intramolecular palladium catalyzed C?H olefination of unactivated aliphatic alkene to install the morphinan ring system.     

Influence of small rings on the thermodynamics of equilibrium self-assembly

The competition between the formation of linear chain clusters and ring structures in an equilibrium self-assembling system is reexamined by developing a new Flory-Huggins type theory that combines an estimate for the loss of configurational entropy ΔS(ring) upon ring formation with the standard treatment of the free energy of a polydisperse solution of linear chains. The excess entropy of ring formation ΔS(ring) is obtained from an analytical fit to exact enumeration data for self-avoiding chains and rings with 30 or fewer steps on a cubic lattice. Illustrative calculations of the spinodal curves and the extent and the average degree of self-assembly highlight the physical conditions for which the cyclic structures impact the thermodynamic characterization of equilibrium self-assembling systems.     

Synthetic studies on azadirachtin: stereoselective construction of the ABCE ring system

A new method for constructing the ABCE ring system of azadirachtin in a stereoselective manner was developed. The synthesis of the model compound features (1) stereoselective construction of the highly hindered C8 quaternary center by an intermolecular addition reaction of an allylborane with an aldehyde and (2) construction of the E ring moiety by the Pd-catalyzed Nazarov cyclization.     

A Convenient Synthesis of Octahydro-pyrazino [ 1,2- a ] pyrazine

The recent research results suggest that a series of octahydro-pyrazino[ 1,2-a ]pyrazines are useful as antiallergic agents.[1] Gubert et al. [2] developed a route from 1,4-dibenzyl-2-ethoxycarbonylpiperazine for the synthesis of this ring system. Under their conditions, this ring system was obtained with a low overall yield in six steps. Optimization of synthetic route to this ring system is still desirable. In this paper, we presented an efficient synthesis of octahydropyrazino[1,2-a]pyrazine by a new and efficient method starting from 1,3-dichloro-2-propanol and N-tosylated diethylenetriamine. The structure of title compound was determined by spectroscopy and X-ray diffraction technique.     

A simple approach for the synthesis of azocine alkaloids: The total synthesis of megallanesine

A new three step synthetic route to construct azocine ring system using anion chemistry and intramolecular Friedel-Craft reaction of an ester is presented. This method allows synthesis of azocine ring analogues in excellent overall yields. The designed strategy was applied for the synthesis of naturally occurring magallanesine.     

Unmasking of aminoanthroquinone moiety through a ring opening in the presence of copper salts and a subsequent cross-coupling/recyclization cascade

In the presence of copper(I) salts, 3-bromo- or 3-iodoisoxazoles undergo isoxazole ring opening to give keto amines that can undergo further one-pot cascade cross-coupling/recyclization transformation into an extended flat polyaromatic ring system that can provide an interesting new platform for the design of DNA intercalators. If necessary, the three-step reaction cascade can be interrupted at a desired intermediate step through a judicious choice of reaction temperature and catalyst.     

Hodgsonox, a new class of sesquiterpene from the liverwort Lepidolaena hodgsoniae. Isolation directed by insecticidal activity

Hodgsonox (1), a new insecticidal sesquiterpene, has been isolated from the New Zealand liverwort Lepidolaena hodgsoniae. The structure was elucidated on the basis of 2D NMR analysis of 1 and a synthetic epoxide derivative (2). Hodgsonox represents a new class of sesquiterpene with a cyclopenta[5,1-c]pyran ring system fused to an oxirane ring. The combination of a mono- and a 1,1 disubstituted double bond flanking the oxygenated carbon of a the pyran ring is a unique structural feature. Hodgsonox is toxic to larvae of the blowfly Lucilia cuprina.     

密封圈低温压缩永久变形测量方法的研究

设计制作了一整套带光学系统的低温压缩永久变形测量系统,应用于密封圈低温环境下的高度测量,实现密封圈低温压缩永久变形测量过程自动化,与国家标准中规定的手动式橡胶试样测量方法相比较,提高测量效率和实用价值.     

Fragmentation of nitrone triflates to 9-membered rings

A new fragmentative rearrangement of nitrone derivatives to form 9-membered rings is reported. The fragmentations are triggered when nitrones are treated with triflic anhydride; a C-C bond antiperiplanar to the cleaving N-O bond is activated either by an oxygen lone pair or by an electron-rich aromatic ring. In the former case, further cyclization of the 9-membered intermediate leads to a rearranged condensed ring system, but when triggered by arenes, 9-membered ring amides are isolated.     

A new total synthesis of an indolo[3,2-j]phenanthridine alkaloid calothrixin B

A new total synthesis of calothrixin B is described. The key step is an allene-mediated electrocyclic reaction involving the indole 2,3-bond for the construction of a suitable 4-oxygenated 2,3,4-trisubstituted carbazole ring system.     

New Synthesis of A‐Ring Aromatic Strigolactone Analogues and Their Evaluation as Plant Hormones in Pea (Pisum sativum)

A new general access to A‐ring aromatic strigolactones, a new class of plant hormones, has been developed. The key transformations include in sequence ring‐closing metathesis, enzymatic kinetic resolution and a radical cyclization with atom transfer to install the tricyclic ABC‐ring system. The activity as plant hormones for the inhibition of shoot branching in pea of various analogues synthesized by this strategy is reported.     

An oxidative entry into the amido trioxadecalin ring system

The amido trioxadecalin ring system is a key structural component of the architecturally interesting anticancer and immunosuppressive agents of the mycalamide, theopederin, and onnamide families of natural products. We report a new entry into this structure in which a mixed acetal serves as a surrogate for a formaldehyde hemiacetal in an addition to an oxidatively generated acyliminium ion. The stereochemical outcome of this process can be explained by the conformational preferences of the product ring system. [reaction: see text]     

Total Synthesis of (−)-Glaucocalyxin A

A practically useful method for the formation of the highly oxygenated bicyclo[3.2.1]octane ring system through Mn(OAc)₃-mediated radical cyclization of alkynyl ketones was developed, which opens up a new avenue for the total synthesis of a number of highly oxidized diterpenoids. Application of this method enabled the first total synthesis of (−)-glaucocalyxin A. Other salient features of the synthesis include a highly enantioselective conjugate addition/acylation cascade reaction, a Yamamoto aldol reaction, and an intramolecular Diels–Alder reaction to assemble the A/B ring system.     

Total Synthesis of (−)‐Glaucocalyxin A

A practically useful method for the formation of the highly oxygenated bicyclo[3.2.1]octane ring system through Mn(OAc)₃‐mediated radical cyclization of alkynyl ketones was developed, which opens up a new avenue for the total synthesis of a number of highly oxidized diterpenoids. Application of this method enabled the first total synthesis of (?)‐glaucocalyxin A. Other salient features of the synthesis include a highly enantioselective conjugate addition/acylation cascade reaction, a Yamamoto aldol reaction, and an intramolecular Diels–Alder reaction to assemble the A/B ring system.     

Synthese und Molekülstruktur neuer Ringsysteme aus 1,1,3,3-Tetrachlor-1,3-diphosphapropan

Synthesis and Molecular Structure of new Ring Systems from 1,1,3,3-Tetrachloro-1,3-diphosphapropane 1,1,3,3-Tetrachloro-1,3-diphosphapropane 1 reacts in two different ways to form new heterocycles. Partial oxidation of 1 with tetrachloroorthobenzoquinone furnishes the methylene-bridged λ³P, λ⁵P species 3 . Subsequent reactions with di- and triethylamine lead to the condensed ring system 6 with the P?C bonds connected to a central four-membered ring. Compound 6 displays crystallographic inversion symmetry, a short transannular P? P distance and an extremely distorted tetrahedral coordination geometry at the four-membered ring phosphorus atoms. 1 reacts with 7 to give the heterocycle 8 with a central eight-membered ring involving four phosphorus atoms. The eight – membered ring shows a ?bent”? crown conformation, the condensed five – membered rings display envelope conformation.     

Experimental and theoretical studies of the redox potentials of cyclic nitroxides

The redox potentials of 25 cyclic nitroxides from four different structural classes (pyrrolidine, piperidine, isoindoline, and azaphenalene) were determined experimentally by cyclic voltammetry in acetonitrile, and also via high-level ab initio molecular orbital calculations. It is shown that the potentials are influenced by the type of ring system, ring substituents and/or groups surrounding the radical moiety. For the pyrrolidine, piperidine, and isoindolines there is excellent agreement (mean absolute deviation of 0.05 V) between the calculated and experimental oxidation potentials; for the azaphenalenes, however, there is an extraordinary discrepancy (mean absolute deviation of 0.60 V), implying that their one-electron oxidation might involve additional processes not considered in the theoretical calculations. This recently developed azaphenalene class of nitroxide represents a new variant of a nitroxide ring fused to an aromatic system and details of the synthesis of five derivatives involving differing aryl substitution are also presented.     

The synthesis of 2-amino-4(3H)-quinazolinones and related heterocycles via a mild electrocyclization of aryl guanidines

A new method for the preparation of 2-amino-4(3H)-quinazolinones and similar fused heterocycles is described. Simply warming a mixture of an aryl guanidine and carbonyl diimidazole in acetonitrile results in formation of a putative N-amidinoisocyanate intermediate which undergoes a 6π-electron electrocyclic reaction with the aryl ring to generate the quinazolinone ring system. The mild conditions are compatible with a variety of functional groups, and the reaction is shown to be successful on multigram scale.