Synthesis and structure of η6-(biphenyl)-η5- (cyclopentadienyl)iron(II) hexaflourophosphates

A series of η⁶-(biphenyl)-η⁵-(cyclopentadienyl)iron(II) hexafluorophosphates have been prepared. Demethylation occured during the synthesis of the 2′-OMe derivatives to yield the correspoding 2′-OH product. The mechanism of this process is discussed. In all cases the complexation involved the unsubstituted phenyl ring. From ¹³C NMR data, values of Hammett resonance parameters σ_R, were calculated which show that the [CpfeC₆H₅]⁺ group behaves as an electron-withdrawing substituent comparable in strength to the cyano group. Approximate values of the biphenyl interplanar angle (θ) were obtained. θ appeared to be significantly lower when electron-releasing substituents were present. ⁵⁷ Fe Mössbauer data support the strong electron acceptor properties of the [CpFe⁺C₆H₅] moiety. In particular the quadrupole splitting (QS) shows a marked increase for the 4-OMe derivative relative to the unsubstituted comples. This is in direct contrast to the aryl ferrocenes. Here, the ferrocenyl and OMe substituents are electronically and so there is no (QS) enhancement.     

Hydrogenation of 6- and 7-alkyl-2-(4′-bromophenyl)indolizines

Hydrogenation of 6- and 7-alkyl-2-(4-bromophenyl)indolizines over rhenium heptasulfide proceeds with hydrodebromination to give a mixture ofcis- andtrans-isomers of 6- and 7-alkyl-2-phenylindolizidines.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1267–1268, July, 1993.     

Syntheses and Structure of Hexacoordinated Selenium (λ6-Selane) and Tellurium (λ6-Tellane) Compounds

The first isolation of bis(2,2′-biphenylylene)dichloro- and difluoro-perchalcogenuranes, [12–Se–6(C4F2)] (λ⁶-selane); [12–Te–6(C4X2), X = Cl, F] (λ⁶-tellane) and the corresponding tellurane Te-oxide dimer [12–Te–6(C4O2)]₂, and their crystal and molecular structures are described. Furthermore, on the basis of the difference between the 3c-4e bonds of the dodecet species and that of the decet species a new molecular orbital concept has been proposed on the 3c-4e bond of perchalcogenurane species [12–M–6, M = chalcogen atoms].     

Enantioselective synthesis of (S)- and (R)-6-hydroxy-8-nonene-carboxylates by asymmetric catalysis: a formal synthesis of (R)-α-lipoic acid and its (S)-antipode

A short and efficient enantioselective synthesis of (S)- and (R)-configured 6-hydroxy-8-nonene-carboxylates — precursors to (R)-α-lipoic acid and its (S)-enantiomer — by allylation of alkoxycarbonyl substituted aldehydes with allyltrimethylstannane and BINOL/Ti(OiPr)₄ catalyst is described. The best results in terms of enantiomeric purity and yield are obtained employing 10 mol% of the titanium-species without molecular sieves.     

A Facile and Highly Stereoselective Reductive Debromination of Anhydro-6- (R)-Hydroxyethyl- 6-Bromopenicillin

Reductive debromination of anhydro-6-(R)-hydroxyethyl-6-bromopenicillin 7 by zinc in ammonium acetate gave 9 in 81% yield with high stereoselectivity of 6-(α):6-(β)=13:1.     

A Facile and Highly Stereoselective Reductive Dcbromination of AnhydrO-6- (R)-Hydroxyethyl- 6-Bromopenicillin

Thetitlecompound,4-acetoxyazetidinone5',hasbeenwidelyusedasanimportantintermediateforpenem,carbapenemandtrinemsynthesisZa~Zfandseveralapproachesto5havebeenreported3a~3c.Thesemisyntheticapproachof4-acetoxyazetidinone5frompenicillinIreportedbyDiNinnoetal.Zbisausefulone,thedebrominationofmethyl6-bromo-6-l(R)-Ihydroxy-ethyllpenicillinate3byzinc-ammoniumacetateaffordedthelabilecompound4.91igmixtureoftransandetsisomers,in92%yieldbutintheformerstepthehydroxyethylationoftheC-6positionofpenicillinat…     

Synthesis of 6(E)- and 6(Z)-(3-ethoxycarbonylpropyl)oximes of 16α,17α-cyclohexanopregn-4-ene-3,6,20-trione and study of their interaction with proteins of the rat uterine cytosol and blood serum

6(E)- and 6(Z)-(3-Ethoxycarbonylpropyl)- and -(3-carboxypropyl)oximes of 16,17-cyclohexanopregn-4-ene-3,6,20-trione were synthesized. The reactions of these ester ligands with pentarane-binding proteins of the uterine cytosol and blood serum were studied; the latter exhibits a higher affinity. The preferred binding of the oxime (E)-isomer relative to the (Z)-isomer was noted.     

Reactions of 1,3-bis(ω-bromoalkyl)-6-methyluracils with 2-(dialkylamino)ethylphosphonates and 2-(dialkylamino)ethyl phosphates

1,3-Bis(4-bromobutyl)-6-methyluracil reacts with diethyl 2-(dimethylamino)ethylphosphonate to form a bisquaternary ammonium salt, whereas the reaction of 1,3-bis-(6-bromohexyl)-6-methyluracil with diethyl 2-(diethylamino)ethyl phosphate gives 1,3-bis-[(6-diethoxyphosphoryloxy)hexyl]-6-methyluracil and 1,1,4,4-tetraethylpiperazinium dibromide. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1130–1132, June, 2000.     

Efficient synthesis of (−)-(R)- and (+)-(S)-rolipram

A novel, efficient and protecting group free enantioselective synthetic approach of (?)-(R)-1 and (+)-(S)-rolipram 2 is described employing the organocatalyzed asymmetric Michael addition, Henry condensation, Wittig olefination and reductive lactamization reactions as key steps.     

Density functional calculations of the structures and bond energies of Cr(CO)6 and (η6-C6H6) Cr(CO)2(CX) (X=O,S) complexes

Summary Quantum chemical calculations based on density functional theory have been performed on Cr(CO)₆, (⁶-C₆H₆)Cr(CO)₃ and (⁶-C₆H₆)Cr(CO)₂(CS) at the local and nonlocal level of theory using different functionals. Good agreement is obtained with experiment for both optimized geometries and metal-ligand binding energies. In particular, a comparison of metal-arene bond energies calculated for the (⁶-C₆H₆)Cr(CO)₃ and (⁶-C₆H₆)Cr(CO)₂(CS) complexes correlates well with kinetic data demonstrating that substitution of one CO group by CS leads to an important labilizing effect of this bond, which may be primarily attributed to a larger -backbonding charge transfer to the CS ligand as compared with CO.     

Analogues of Moranoline and Mdl 73945. Methyl 6(5)-Deoxy-6(5)-(Morpholin-4-Yl)-α-D-Glycosides as Glucosidase Inhibitors

ABSTRACT

Methyl 2,3,4-tri-O-acetyl-6-O-(p-tolylsulfonyl)-α-D-glucopyranoside (6), or its iodo analogue 7, were subjected to nucleophilic displacement with morpholine to give 8, deacetylation of which gave methyl 6-deoxy-6-(morpholin-4-yl)-α-D-glucopyranoside (3). Similarly, 11, 12 and 21 were prepared. The 6-deoxy-6-iodo derivative 16 was subjected to nucleophilic displacement with morpholine and subsequent acetylation to give 15. Deacetylation of 15 gave 17. The kinetic studies for the inhibition of β-D-glucosidase from sweet almond and using o-nitrophenyl β-D-glucopyranoside as substrate exhibited a K _i value for 21 on the same order as 1-deoxynojirimycin whereas for 3, a K _i value of lesser order was observed.     

Total Synthesis of (-)-Kaerophyllin,(-)-Hinokinin and (±)-Isohinokinin

Kaerophyllin (1) ,hinokinin (2 )andtheiranalogue isohinokinin (3)belongtothedibenzylbutyrolactone lig nans .Kaerophyllin (1)wasisolatedfromtherootofspot tedcowparsley (ChaerophyllummaculatumWilld .) 1andhinokinin (2 )wasisolatedfromtheheartwoodofLiboce drusformosanaFlorin .2 AccordingtoMacRaeandTow ers ,3afivememberedlactoneringandamethylenedioxylgroupwereimportantstructuralcharacteristicswhichcon tributetotheactivityoflignansasantitumoragents .More over ,anunsaturateddoublebondbetweenC3—…     

Efficient synthesis of (S)-(−)- and (R)-(+)-enantiomers of 15-deoxyspergualin (15-DSG)

An efficient synthesis of the (S)-(−)- and (R)-(+)-enantiomers of 15-deoxyspergualin (15-DSG) is reported. The synthesis involves preparative HPLC separation and subsequent hydrogenolysis of two diastereoisomers 10a and 10b of fully protected 15-DSG penultimates. Alternatively, diastereomerically pure amide 10b (97% de) was also prepared from acid 8b (97% de), which was obtained via crystallization of a 1:1 diastereomeric mixture of 8a and 8b.     

A concise total synthesis of (±)- and (-)-okilactomycin D

The spirotetronate okilactomycin D (7) has been efficiently synthesized by a route featuring a substrate-controlled, diastereoselective (8:1) intramolecular Diels-Alder (IMDA) reaction of 11. The assigned absolute configuration of (-)-7 was confirmed.     

Complexation of 6-Deoxy-6-(aminoethyl)amino-β-cyclodextrin with Sodium Cholate and Sodium Deoxycholate

In order to study its guest binding and the inclusion phenomena, 6-deoxy-6-(aminoethyl)amino--cyclodextrin (CDN) was synthesised and its binding properties examined. The complexation phenomena of sodium cholate (NaC) and sodium deoxycholate (NaDC) with CDN has been monitored by the NMR method using ¹³C chemical shift data. The method of continuous variation Job's method has been used to determine the stoichiometry of these supramolecular complexes. The Job's plot confirms the 1 : 1 supramolecular complex for NaC: CDN and the 1 : 2 supramolecular complex for NaDC: CDN. The interaction of NaC and NaDC with CDN has been obtained through two-dimensional Rotational Nuclear Overhauser Effect Spectroscopy (ROESY) NMR. Equilibrium constants were also obtained from ¹³C chemical shift data (C-1, C-3 & C-4) at different pH values (7, 9, & 11).     

1,3-Dipolar cycloaddition reaction of nitrone η6-(arene)chromium tricarbonyl complexes with styrene and η6-(styrene)chromium tricarbonyl

The products of 1,3-dipolar cycloaddition of the nitrone-type η⁶-(arene)chromium tricarbonyl complexes (CO)₃CrC₆H₅CH=N⁺(O^?)R, where R = Me, Ph, Bu^t, with styrene and η⁶-(styrene)chromium tricarbonyl were obtained and characterized by a combination of physicochemical methods. This type of reactions proceeded with very high regio- and stereoselectivity to exclusively form cis-2,3,5-tri-substituted isoxazolidines.     

Synthesis of (S)-(−)-β-cuparenone and (S)-(−)-cuparene

A short and efficient synthesis of the title compounds is described. (S)-(−)-β-Cuparenone was prepared in 31% yield from p-tolualdehyde and mesityl oxide in eight steps. Absolute stereochemistry was established by means of a diastereoselective cyclopropanation using (R,R)-hydrobenzoin as a recoverable auxiliary.     

Total syntheses of (±)-securinine and (±)- allosecurinine

Total syntheses of (±)-securinine and (±)-allosecurinine that employ a tandem rhodium carbenoid-initiated Claisen/α-ketol rearrangement sequence as a key step are described.