Synthesis of the anti and syn isomers of thieno[f,f ']bis[1]benzothiophene. Comparison of the optical and electrochemical properties of the anti and syn isomers

We report isomer-pure synthesis of thieno[2,3-f:5,4-f ']bis[1]benzothiophene and thieno[3,2-f:4,5-f ']bis[1]benzothiophene, the anti and syn isomers of a pentacyclic compound consisting of alternating thiophene and benzene rings. The optical and electrochemical properties of both are reported. In the anti isomer, the ribbonlike embedding of three thiophene units leads to a near-planar molecule with favorable pi-pi stacking behavior in the solid state as shown by X-ray crystal structure analysis.     

Synthesis and structures of sila-macrobicyclic compounds: syn and anti isomers of hexasilabicyclo[12.8.8]triacontane

Syn and anti isomers of a novel saturated sila-macrobicyclic compound, hexasilabicyclo[12.8.8]triacontane, were synthesized via the functionalization of 1,1,10,10-tetraphenylhexasilacyclooctadecane derivative, which was obtained by the diimide hydrogenation of the corresponding hexasilacyclooctadecahexayne derivative. The structures of these macrocyclic compounds were determined by ¹H, ¹³C, and²⁹Si NMR and X-ray crystallography.     

Syntheses of 5H-benzoxazolo[3,2-a] quinolin-5-ones

Treatment of N-(2-hydroxyphenyl)anthranilic acid with acetic anhydride, under refluxing conditions provided a simple method for the synthesis of 5H-henzoxazolo[3,2-a] quinolin-5-one (IVa), a heretofore unreported ring system. When propionic anhydride was used in the above reaction, 6-methyl-5H-benzoxazolo[3,2-a]quinolin-5-one (Va) was obtained. Other examples prepared in this fashion were IVb, IVc and Vb. Treatment of IVa with methoxyethylamine afforded 1,2-dihydro-1-(2-hydroxyphenyl)-2-(methoxyethylimino)-4-quinolinol (VII). A possible mechanism for the cyclization reaction is discussed.     

Synthesis of anti and syn hydroxy-iso-evoninic acids

The first synthesis of hydroxy-iso-evoninic acid (2), a pyridyl diacid found as a macrodilactone bridging ligand in bioactive Celastraceae sesquiterpenoid-based natural products, has been achieved in 9 steps and an overall yield of 26%. The synthesis utilizes a benzilic ester rearrangement (BER) and a late stage benzylic oxidation to give access to all four stereoisomers whose absolute stereochemistry was assigned following chromatographic separation and anomalous dispersion X-ray crystallography.     

A Novel Phenylene Topology: Total Syntheses of Zigzag [4]- and [5]Phenylene

In agreement with theory , the title compounds 1 and 2, which were prepared by CpCo-catalyzed cycloisomerizations of appropriate oligoalkynylbenzenes, display physical properties that are in contrast with those of the corresponding linear isomers, but that are very similar to those of the angular topomers.     

Study of [Thienylene-dialkoxy phenylene] Conjugated Materials

Summary: In this work we report on the electrochromic and optical studies of thin films of thienylene-dialkoxyphenylene. The films for the optical measurements were prepared by spin casting on glass and silicon substrates. Photoluminescence and absorption spectra were recorded in the temperature range from 300 K. The differences between the spectra of the polymer and the oligomer can be attributed to a higher mean conjugation length in the polymer than in the oligomer. We present also a first principles theoretical calculation which shows that the conjugated oligomer has an HOMO-LUMO energy around 2.0 eV, which is consistent with the experimental data.     

Synthesis of syn and anti isomers of trans-cyclopropyl arginine

There is currently considerable interest in arginine and its structural analogues in the context of nitric oxide synthase (NOS) substrates and inhibitors. Of particular interest are conformationally constrained arginine analogues used to probe the active sites of the three NOS isoforms. A simple procedure is described for the preparation of syn- and anti-trans-cyclopropyl arginine starting from the alpha-OBO-protected Cbz-dehydroglutamate. Cyclopropanation is effected by diazomethane addition followed by irradiation of the resulting pyrazoline and gives a 3:1 mixture of syn:anti isomers that can be separated by crystallization. Reduction of the ester to the alcohol followed by guanylation gives the fully protected cyclopropyl arginine analogues. The CBZ protecting groups are removed by hydrogenolysis and the OBO by mild acid treatment followed by base hydrolysis.     

Syntheses of a pillar[4]arene[1]quinone and a difunctionalized pillar[5]arene by partial oxidation

A pillar[4]arene[1]quinone and a difunctionalized pillar[5]arene have been synthesized by partial oxidation.     

Regioselective Syntheses of 1-Aryl-substituted-5H-[1,3]thiazolo[3,2-a]quinazoline-5-ones During Sonogashira Coupling

Abstract

Reaction of 2-mercaptopropargylquinazoline-4-one with various aryliodides catalyzed by Pd–Cu leads to the regioselective formation of 1-arylsubstituted-5H-[1,3]thiazolo-[3,2-a]quinazoline-5-ones.

GRAPHICAL ABSTRACT      

Syntheses of 1,3-disubstituted imidazo[l,5-a]pyridines

Facile syntheses of 1,3-disubstituted imidazo[l,5-a]pyridines have been effected by treatment of ketimines derived from di-2-pyridyl ketone with LDA and benzophenone, reactions of benzyl amine with di-2-pyridyl ketone in boron trifluoride etherate, and reaction of di-2-pyridyl methanamine imines with molecular sieves in benzene.     

Syntheses of seven-membered rings: ruthenium-catalyzed intramolecular [5+2] cycloadditions

The Ru-catalyzed intramolecular [5+2] cycloaddition of cyclopropylenynes is investigated with respect to the regio- and diastereoselectivity as well as the functional group compatibility of the reaction. Evidence for the mechanism as occurring through a ruthenacyclopentene intermediate is elucidated from 1) the study of the diastereoselectivity of the cycloaddition; 2) the effect of variation of substituents on the regioselectivity of cyclopropyl bond cleavage in 1,2-trans- and 1,2-cis-disubstituted cyclopropanes and 3) examples that clearly do not involve ruthenacyclohexene as intermediates as products still incorporate the cyclopropyl moiety. The scope and limitations of the Ru-catalyzed cycloaddition are discussed and compared with the Rh-catalyzed reaction. The potential power of this methodology towards natural product total synthesis is demonstrated by the formation of several polycyclic systems with the chosen reaction conditions and readily available cyclopropylenyne substrates.     

The syn and anti Steric Course in Bimolecular Olefin-Forming Eliminations

Earlier evidence led to the view that in bimolecular olefin-forming eliminations the anti steric course is generally preferred over the syn. Recent experiments, however, show that in some common bimolecular elimination reactions, notably those involving onium bases, syn- and anti-eliminations proceed side by side, the former preferentially leading to the trans- and the latter to the cis-olefins.     

Syntheses of polythia[n]ruthenocenophanes

Thiacrown ethers containing ruthenocene as a subunit were synthesized by the reaction of 1,1′-bis(3-chloropropyl-1-thia)ruthenocene with disodium dithiolates in THF/EtOH. In these reactions, some unexpected products were obtained.     

Syntheses of Oxazolo [4,5-b]pyridines and [4,5-d]pyrimidines

Oxazolo [4, 5-b] pyridines and [4, 5-d] pyrimidines and their 2-substituted compounds have been prepared respectively by condensation of orthoesters or thioimidates derivatives with 2-amino-3-hydroxypyridine and 4-amino-5-hydroxypyrimidine.     

Syntheses and reactions of [1,3,4]thiadiazolo[3,2-a]pyrimidinone derivatives

5-Imino-6H-7-one, 7-amino-5-one and 5-isocyano-7-one derivatives of [1,3,4]thiadiazolo- and -[1,3]thiazolo-[3,2-a]pyrimidines were synthesized. 5-Isocyano-7-one derivatives were obtained by the reaction of the corresponding 5-imino-6H-7-ones with the Vilsmeier reagent in one step.     

内-α-取代-α-甲基双环[2.2.1]-5-庚烯-2-基甲醇的合成及香气

许多降冰片烷衍生物可以作为食品或化妆品香精中的香原料,如珍贵的天然檀香油中的主要成份β-檀香醇(?)近年来又有许多其它作为香原料的降冰片烷衍生物的报道,例如具有如下通式的化合物     

The infrared spectra and normal coordinate analysis of syn and anti acetaldoxime

The infrared spectra of mixtures of syn and anti acetaldoxime and its deuterated analogues CH₃CHNOD, CD₃CHNOH, CD₃CDNOH and CH₃CDNOH have been recorded. The syn and anti isomers of CH₃CHNOH, CD₃CHNOH, CD₃CDNOH and CH₃CDNOH have been separated by gas chromatography [1]. The infrared spectra of separated isomers in CS₂ solution have been recorded and the assignment of ten in-plane vibrations made. From a normal coordinate analysis the Urey-Bradley force field, the potential energy distribution and additional information about assignments have been obtained.For the anti isomer the simple Urey-Bradley force field gives satisfactory agreement between the calculated and measured frequencies. For the syn isomer it is necessary to take into account the interactions between atoms separated by three bonds.