Letters in Organic Chemistry - Volume 6, Issue 8, 2009

Organocatalytic asymmetric domino sulfa-Michael/aldol condensation reactions between 1,4-dithiane-2,5-diol (the dimer of mercaptoacetaldehyde) and cinnamaldehydes were efficiently promoted by (S)-diphenylprolinol TMS ether in the presence of bile acid derivatives, leading to hitherto unknown 4,5-dihydrothiophene-2-carbaldehydes in moderate to good yields and good enantioselectivities.

The inclusion of ethylammonium, N-methylpyridinium cations and native L-α-amino acids by the watersoluble pentasulfonatocalix[5]arene 1 has been investigated at neutral pH by 1H NMR. The complexation behavior has been compared with that of the homologous tetrasulfonatocalix[4]arene 2. Unlike host 2, host 1 exhibits high selectivity in the recognition of the investigated guests.

β-Cyclodextrin derivatives with varying lengths of π-conjugated arms have been synthesized. Their structures have been confirmed by 1H NMR, elemental analysis, mass spectrometry and X-ray crystal structure determination. Their self-inclusion properties are evaluated using Circular Dichroism, 1D and 2D 1H NMR measurements. It is found that, when the length of the π-conjugated arm is extended from 4 to 5 and to Read More

A simple method for the straightforward regioselective synthesis of 2,3-mannoepoxy-β-cyclodextrin, which is a valuable precursor for further functionalization of β-cyclodextrin, is achieved in one pot at a moderate yield.

An efficient synthesis of taxotere side chain has been achieved using Shibasaki's asymmetric Henry reaction as the key step.

Ion exchange resin catalyzed multicomponent Biginelli reaction is studied for the synthesis of 3,4- dihydropyrimidin-2-ones. Among the various solid acid catalysts Indion-130 was found to be most efficient, recyclable and environmentally benign heterogeneous catalyst regarding reaction time, yield and ease of work up procedure.

An easy solid phase synthesis of oxytocin analogues conjugated to polyaminopolycarboxylic ligand, such as diethylenetriaminepentaacetic acid (DTPA) and tetraazacyclododecanetetraacetic acid (DOTA) is reported. These new products can be labeled with suitable radiometals (e.g. 90Y, 111In, 177Lu), giving rise to radiopharmaceuticals with potential application in imaging and/or therapy of tumors over-expressing oxytoc Read More

A gold (III)-catalyzed hydration of homopropargyl alcohols led to the corresponding γ-hydroxy ketones, which were directly reduced by Ph3SiH in the presence of a Lewis acid, to afford the expected 2,5-disubstituted tetrahydrofurans as a diastereomeric mixture. NMR analysis of the compounds so obtained allowed us to confirm that the cis isomers were the major isomers that can be used for the preparation of new products.

Both aliphatic and aromatic acyl cyanides have been synthesized with TMSCN and acyl chloride with ZnI2 (0.5 mol%). However the in situ generated I2 is proposed accounting for the formation of by-product O-TMS enolate at high catalyst loading rather than 0.5 mol%. Asymmetric reduction of benzoyl cyanide with borane has been explored in 82% yield and 24% ee.

Novel 15N-isotope enriched potassium and diammonium thiophosphoramidates were synthesized and their spectroscopic properties, along with reactivity towards several compounds, including histidine, thymidine, glucose and 2- deoxyribose are presented. The application of quantum mechanical DFT calculations for estimation of 31P NMR chemical shifts for several thiophosphoramidate ions and its derivatives are also discussed.

A method for the facile preparation of N-tosyl-L-phenylalanine chloromethyl ketone was developed. LPhenylalanine was tosylated and converted to the activated ester of p-nitrophenol. Subsequent reaction with dimethylsulfoxonium methylide and treatment with lithium chloride and methanesulfonic acid afforded the α- chloroketone. This practical procedure avoided the use of toxic and explosive diazomethane.

Reaction of atomic carbon with isomeric cresols generates methyltropones and xylenols. Methyltropone to xylenol ratio was found to be highest for m-cresol and lowest for p-cresol. Stability of singlet carbenes produced after insertion of atomic carbon into C-H bonds of cresols plays an important role in the observed ratios.

An efficient aza-Michael addition of amines to a variety of activated olefins was carried out under solvent free conditions using iodine-alumina as a catalyst at room temperature or under microwave irradiation (in case of solid) in high yield.

Synthesis of a building block based on 6,6'-(1H-pyrazole-1,3-diyl)bis(pyridine) (3) that allows introduction of photoluminescent lanthanide(III) chelates to the synthetic oligopeptides on solid phase using the standard Fmoc chemistry is described. Since the ligand based on (3) forms luminescent chelates with Eu3+, Sm3+, Tb3+ and Dy3+ ions, the ligand is highly useful for multiparametric homogenous assays simplif Read More

A rapid and efficient procedure under microwave irradiation, using silica gel-supported reagents for the synthesis of substitued oxazoles has been developed through iron trichloride catalyzed propargylation/cycloisomerization tandem reaction of propargylic acetates and amides.

The ability of the pyridinium adduct of 1,3-dimethyl-5-methylenebarbituric acid (2) to undergo nucleophilic substitution reaction has been examined. Various types of nucleophiles, including cyanide, barbiturate, sulfide anions and 1,2-bis(diphenylphosphino)ethane substitute the pyridinium fragment in 2 leading to synthesis of new organic derivatives.