Showing papers in "Tetrahedron Letters in 1991"

TL;DR: These compounds are compounds consisting of a plurality of nucleosides which are covalently linked by at least one aminoalkylphosphoramidate linkage of the formula ##STR1## wherein n=2 to 6 and Nu1 and Nu2 represent nucleoside phosphates.

TL;DR: In this paper, triluforomethylated aromatic compounds with sodium trifluoromethanesulfinate and t-butyl hydroperoxide are described.

TL;DR: In this article, the lithium alkoxides formed as intermediates undergo an intramolecular addition to the neighboring CN group followed by an S to 0 benzothiazole transfer and simultaneous extrustion of sulfur dioxide and ejection of 2(3H)-benzothiazolone anion.

TL;DR: In this article, a modification of the Mitsunobu protocol for effecting stereochemical inversions of alcohols has been discovered in which use of p-nitrobenzoic acid as the nucleophilic partner results in significantly improved yields with relatively hindered substrates.

TL;DR: In this article, the knoevenagel condensation of carbonyl substrates with acidic methylene reagents proceeds smoothly in presence of zinc chloride, without the need for solvent, to produce products of good purity in high yield.

TL;DR: The Cu(I) complexes of new bisoxazolines (3,7) prepared from the corresponding amino alcohols and malono-bis-imidate exhibit high enantioselectivity of up to 94 %ee in the catalytic cyclopropanation of trisubstituted and unsymmetrical cis-1,2-disubstitized olefins as discussed by the authors.

TL;DR: In this article, aldehydes and ketones were allylated with indium metal in aqueous media without the need of any promoter, and the reaction can be extended to the synthesis of 2-methylene-γ-lactone 6 via the condensation of carbonyl compounds with 2-bromomethylacrylate 4.

TL;DR: Large scale synthesis, oligonucleotides up to 100 bases long, and mixed phosphorothioate/phosphodiester DNA are demonstrated.

TL;DR: The main product of N-methylated amino acid coupling, when oxybenzotriazole is present in the reagent (BOP, PyBOP or HBPyU) or as an additive (DCC/HOBt), is the weakly reactive benzotrizolyl ester as discussed by the authors.

TL;DR: In this paper, the hericenones C (3), D (4), and D (5 ) from the mushroom Hericium erinaceum were determined by interpretation of the spectral data, and chemical and enzymatic reactions.

TL;DR: In this paper, the isolation and structural characterisation of pateamine 1, a thiazole-containing macrolide with the rare dilactone functionality, was reported.

TL;DR: In this paper, α-fucosylation with the reactive trichloroacetimidate 1 as donor and disaccharides 2 and 4 as acceptors led to a remarkable increase in yield under "inverse conditions" i.e. addition of the donor to an acceptor/catalyst solution.

TL;DR: A biologically active constituent, bearing similarities to the annonacin group of Annonaceous acetogenins, has been isolated from the seeds of Annona muricata and the absolute configuration about the tetrahydrofuran ring of ann onacin is proposed.

TL;DR: BINAP produces BINAP-Ru(II) complexes, which act as catalysts for the highly enantioselective hydrogenation of functionalized ketones as mentioned in this paper, and

TL;DR: In this paper, a practical and highly effective process for the asymmetric epoxidation of several 2,2-dimethylchromene derivatives is reported, and this method has been applied to the synthesis of two recently developed antihypertensive agents in enantiomerically pure form.

TL;DR: Anhydrous MnBr 2 and CoCl 2 in conjunction with chiral ephedrine ligands effect substantial asymmetric induction in cycloadducts derived from methyl acrylate and imines of glycine methyl ester.

TL;DR: In this article, Mosher's acid is treated with oxalyl chloride in the presence of DMF in hexane, which is suitable for use without further purification and is amenable to microscale.

TL;DR: In this paper, the authors compared the rate of several Diels-Alder reactions under conventional or microwave heating at the same bulk temperature, and showed that the activating effect of microwaves under homogeneous conditions is specific.

TL;DR: Chiral N-protected β-amino alcohols are easily obtained by NaBH 4 reduction of mixed anhydrides of N -protected αamino acids in an organic/aqueous medium as mentioned in this paper.

TL;DR: Chiral (salen)manganese(III) complexes (3 and 4 ) were prepared and used for the enantioselective epoxidation of unfunctionalized olfefins as mentioned in this paper.

TL;DR: In this paper, a multi-factored complex of structurally unique macrolides was isolated from culture broths of a new species of Saccharopolyspora, which consists of a 5,6,5-cis-anti-trans-tricyclic ring system fused to a 12-membered macrocyclic lactone, which was further substituted by an amino- and a neutral sugar.

TL;DR: The outcome of the coupling of aromatic halides with allylic alcohols can be highly controlled and the reaction directed at will towards the formation of either β-aromatic carbonyl or β -aromatic α,β-unsaturated alcohol compounds as discussed by the authors.

TL;DR: In this paper, the modified Mosher's method was applied to the N -MTPA derivatives of several amino acid esters and acyclic amines and it was shown that this method may be generally used to determine the absolute configurations of the α-carbons of amino compounds of less than 1 mg amount.

TL;DR: A novel and useful method for the azidation of aromatic compounds by the reaction of hypervalent iodine reagent, phenyliodine(III) bis(trifluoroacetate) (PIFA) in 1,1, 1,3, 3,3-hexafluoro-2-propanol followed by treatment of trimethylsilyl azide (TMSA) was developed.

TL;DR: In this paper, a general method for the solid phase synthesis of cyclic peptides containing an Asp residue in their sequence is described. Butts et al. proposed a method for synthesizing cyclic compounds containing an ASP residue in the sequence.

TL;DR: Asymmetric epoxidation of conjugated dienes and enynes catalyzed by (salen)Mn(III) complex 1 takes place with high chemoselectivity to afford monoepoxides exclusively as discussed by the authors.

TL;DR: Palladium catalysed cyclisations creating products possessing spiro-, fused-and bridged-rings, and tetrasubstituted carbon centres as mixtures of double bond isomers are modified to give single products in the presence of Tl(1) salts.

TL;DR: In this paper, the p-fluorine substituents of the starting porphyrin were replaced by NR 2, OR or SR groups in yields between 70 and 90%.

TL;DR: The title complexes recognize various aromatic compounds in D2O as mentioned in this paper, and the complexation is attributed to interactions in the cavity including hydrophobic, electrostatic, and charge transfer interactions.