Letters in Organic Chemistry - Volume 2, Issue 5, 2005

Recent advances in enantioselective catalysis with chiral Brønsted acids and Brnsted bases are reviewed. These catalysts are capable of highly enantioselective amination, aza-Henry, conjugate addition, Friedel-Crafts alkylation, Mannich, and Morita-Baylis-Hillman reactions.

A facile method for synthesis and isolation of chiral isocyanate-phenols, obtained from the reactions of L-tyrosine and L-DOPA [L-3-(3,4-dihydroxyphenyl)alanine] derivatives with di-tert-butyltricarbonate (DBTC), is described. Reaction of the obtained isocyanate-phenol with n-butylamine gave the corresponding chiral unsymmetrical urea.

The one-pot reaction of arylboronic acids with lead tetraacetate in chloroform followed by treatment with 3,4-dimethylaniline in the presence of catalytic copper diacetate gave the corresponding diarylamines under neutral conditions in good to high yields. The reaction proceeded with electron-rich as well as with electron-depleted arylboronic derivatives.

A gold-catalyzed direct addition of alkynes to active acyl iminium ion, which was generated in situ with an acid chloride, to afford a propargylamides in excellent yields.

Microwave (MW) irradiation has been used in each step for the transformation of acyl glycines 2 to 6-benzyl-3-thioxo-2,3,4,5-tetrahydro-1,2,4-triazin-5-one (7a), and its 4-phenyl derivatives 7b and 7c. The oxazolone 3a was also transformed to phenylpyruvic acid 5, whose thiosemicarbazone 6 can be cyclized to 7a under MW. Methylation of 7c gave the respective S- and / or N-methylated derivatives, 8 and Read More

An efficient route to the synthesis of novel fused pyrimidotriazepine derivatives using inorganic solid supports under MWs is described herein. The methodology uses microwave as an alternative heating source, which eliminates the usage of solvent during the course of reaction. With this environmentally benign approach, the reaction time is brought down from hours to minutes along with the yield enhancement. In additi Read More

Two H-shaped supramolecular complexes (C44H28N4Zn)2.(C10H8N2O2).2(CH2ClCH2Cl) 1, (C44H28N4Zn)2.(C6H12N4).(CH2ClCH2Cl) 2 have been prepared and characterized by single-crystal X-ray diffraction.

Synthetic phosphate Na2CaP2O7 has been utilized as an efficient catalyst for the three components coupling of carbonyl compounds, aromatic and aliphatic amines and dialkyl phosphite to produce α-amino phosphonates. The reaction was carried out under solvent-free conditions at room temperature. The by-product H2O formed during the reaction increases the catalytic activity of Na2CaP2O7.

The synthesis of N-(o-aryl)-4-alkyl-thiazolin-2-one atropisomers bearing hydroxy-, methoxy-, amino- or isothiocyanato- groups as ortho-substituent are described from their thiazoline-2-thione analogues. The enantiomers were obtained optically pure by semi-preparative chiral HPLC, their optical properties and absolute configurations were established. The barriers to rotation were determined and are discussed according to the n Read More

A great variety of amides were effectively isolated in high yields from the reaction of ketones and hydroxylamine hydrochloride in the presence of alumina supported sodium hydrogen sulfate catalyst in dry media under microwave irradiation in solvent-free conditions. The major products were formed by the migration of the aryl group of the intermediate ketoximes during Beckmann rearrangement. The catalyst can be reused Read More

The trifluoro analogue 1 of Casodex® was synthesized in racemic form, according to a strategy based on the use of trifluoropyruvate as a key starting material. This compound showed significant in vitro antiproliferative activity on the human prostate cancer cell line LNCaP.

An efficient synthesis of glycosyl dihydropyrimidinones using a three-component reaction of a α- keto ester, glycosyl aldehyde, urea (or thiourea) in the presence of tetrabutylammonium hydrogensulphate and diethylene glycol as eco-friendly solvent has been reported. The reaction has been extended to the synthesis of aryl dihydropyrimidinones also. The glycosyl dihydropyrimidinones were obtained in excellent yields in less t Read More

Sulfamic acid catalyses the one-pot three components coupling of aldehydes, anilines and electron rich dienophiles such as dihydropyran, dihydrofuran and ethyl vinylether resulting in the formation of pyrano, furano and ethoxy benzopyrans.

A methanolic extract of Leontodon rigens (Dryander in Aiton) Paiva & Ormonde yielded 1,10- epoxy-14-hydroxyhypocretenolide-β-D-glucopyranoside and its 6'-O-p-hydroxyphenylacetyl derivative. These compounds represent the first epoxyguaian-12,5-olide derivatives. The structures were established by means of high resolution mass spectrometry and 1-D and 2-D NMR spectroscopy. The cytotoxicity of the i Read More

A mild and effective method was developed for direct α-iodofunctionalisation of ketones using elemental iodine activated by 30 % aqueous hydrogen peroxide in the presence of acidic catalyst.

Using quantum chemical methodology, we reinvestigate the aromaticity of the much debated arsole, using the newly developed gauge-including magnetically induced currents (GIMIC) method. GIMIC provides a quantitative measure of the induced ring current strength, showing arsole to be moderately aromatic. Comparison is made with pyrrole, phosphole, and cyclopentadiene.

A new synthetic methodology to obtain polyfunctionalized cycloheptane synthons, with up to four stereocenters, is presented. Three key processes are involved in this methodology: first, the synthesis of C1- functionalized 8-oxabicyclo[3.2.1]oct-6-en-3-ones by a [4+3] cycloaddition reaction; second, the stereoselective reduction of the carbonyl group on C3 and third, the hydrolytic cleavage of the oxygen bridge of the cycload Read More

A methodology to obtain polyfunctionalized cycloheptane synthons, with five stereocenters, is presented. The precursors are C1-functionalized 8-oxabicyclo[3.2.1]oct-6-en-3-ones, obtained by a [4+3] cycloaddition reaction. The stereoselective reduction of the carbonyl group on C3 of these cycloadducts, followed by an electrophilic addition of organic acids on the C6-C7 double bond, under controlled conditions, allows the int Read More