Letters in Organic Chemistry - Volume 2, Issue 7, 2005

The invention of new methods and strategies for stereoselective glycoside synthesis and convergent oligosaccharide assembly has been critical for the area of glycosciences. At the heart of this account is the discussion of the strategies for convergent oligosaccharide synthesis that have emerged during the past two decades. The introductory part provides general background information and describes the key features o Read More

We report the preparation of 5,11,17,23-tetra(tert-butyl)-25,27-bis(ethoxymethoxy)-26,28- bis(diethylaminocarbonylmethoxy)calix[4]arene 1 and its binding properties towards alkali and alkaline-earth cations.

C60H2 was prepared in high yield by the reduction of C60 with either NaBH4 or Hantzsch esters. Dehydrogenation of hydrofullerenes to C60 by both organic and inorganic bases in the presence of air was achieved in 90-99% yield. Possible pathways for the conversion of C60H2 to C60 are proposed.

The synthesis of hitherto unknown (pyrazol-4-yl)-1,3,4-oxadiazoles and 1,3,4-oxadiazolines is described. They were all synthesized in one or two steps from the hydrazide 2.

The reaction of AgNO2/TMSCl with olefins affords nitrosonitrate, which are converted into α- nitroximes in good yield. Both nitrosonitrate and nitroximes are converted with acids into furoxane in high yield. The reaction of AgNO2 with TMSCl furnished first N2O3 and hexamethylsiloxane. The nitroso nitrates are obtained by addition of N2O3 to the olefines.

The use of easily accessible N-monosubstituted 1,2-diphenyl-2-aminoethanols as ligands to promote the asymmetric addition of diethylzinc to alkyl- and arylimines generated in situ from the precursors provided optically active N-diphenylphosphinylamines with enantioselectivities of up to 96% ee.

1,2,3,4,5,6-Hexahydrophosphinine oxides with exocyclic P-function in position 3 can be obtained in a diastereoselective manner by the two-step conversion of 1,2-dihydrophosphinine oxides. Michael addition of the >P(O)H species on the α,β-double-bond of the starting P-cycle is followed by catalytic hydrogenation of the 1,2,3,6-tetrahydrophosphinine oxides so obtained. One of the bis(phosphine oxides) served, after deoxyg Read More

This paper describes a convenient procedure for the synthesis of dinucleosides via cross metathesis using microwave activation.

Reactions of N-, C-, and S-nucleophiles with 3-nitro-2-trifluoro(or trichloro)methyl-2H-chromenes proceeded via nucleophilic addition at the double bond to give 2,3,4-trisubstituted chromans in good to moderate yields. Stereochemical and conformational preferences of 2,3,4-trisubstituted chromans were studied.

The reactivity of N,N'-bis[(E)-dimethylamino)methylene]urea (1) with amines is described. Selective exchange of one of the N,N-dimethylamino fragments is possible with most of the benzylic amines tested, allowing the formation of 1-(alkylamino-methylene)-3-dimethylaminomethylene ureas as analytically pure precipitates in modest yields. Under acidic conditions, the urea fragment acts as leaving group leading the for Read More

Influence of numerous parameters (solvent, base, coupling reagent) in the coupling of conjugated carboxylic acid with methyl ester amino acids hydrochloride, allowing the synthesis of various substituted amino acid derivatives, has been investigated. Usefulness of this method is illustrated in the synthesis of trans-clovamide. This natural polyphenol compound, whose synthesis is correlated with resistance to plant disease, pres Read More

Y-27632 and its enantiomer were synthesized in 8 steps from trans-1,4-cyclohexanedicarboxylic acid by using a diastereoselective reductive amination of a ketone.

A novel and efficient synthesis of 4-substituted 2-oxazolidinones is described; the synthesis utilizes Sharpless asymmetric dihydroxylation (AD) of appropriately substituted O-allylcarbamates and intramolecular cyclisation as key steps.

A diastereoselective reaction of 3-methyl-1H-phenalen-1-one (6) with Lawesson's reagent afforded 8a,15a-dihydro-7,8a,16-trimethyl-7,16-epoxy-7H,15H,16H-naphtho[1,8-ef]phenaleno[1,2-b]oxocin-15-one (10), in 82% yield. The formation mechanism of 10 involves a Michael addition of a naphthopyrane intermediate to 6, followed by an intramolecular aldol condensation. The structure of a single enantiomer of 10 (7R, 8aR Read More

In situ generation of hydrogen iodide from cesium iodide/p-toluenesulphonic acid was found to be an attractive reagent for the conversion of alkyl, allyl and benzyl alcohols to their corresponding iodides in different solvents under mild conditions.

An enolate synthon of alkoxyacetone was regioselectively generated using alkoxyallene oxide and titanium tetraiodide/titanium tetraisopropoxide, and the subsequent conjugate addition reaction with enones gave 4-alkoxy-1,5-diketones in good yields.

A novel reagent tetrabutylammonium halide has been utilized for the highly regioselective ring opening of oxiranes to halohydrins at room temperature in good yields involving β-cyclodextrin in aqueous medium.

The low reactivity of pyridine, pyridazine, pyrazine, and pyrimidine towards electrophilic substitution reactions can be explained assuming a frontier orbitals control of the reaction. In fact, DFT study of the molecular orbitals of these molecules shows that the HOMOs of these substrates are not π orbitals. Furthermore, the change in the reactivity observed in pyridine-N-oxide can be explained considering that, in this case, the HOM Read More