Tamás Patonay

Enantioselective epoxidation of 2,2-dimethyl-2H-chromenes by dimethyldioxirane and jacobsen's Mn(III)salen catalysts

Enantioselective epoxidation of 2,2-dimethyl-2H-chromenes 1a-d has been performed by the Mn(III)salen complexes (R,R)-3 and (S,S)-3 as catalysts and dimethyldioxirane (DMD) as oxygen donor. The epoxychromans 2a-d were obtained in good yields and high enantioselectivities (up to 93% e.e.), which constitute the first examples of enantioselective epoxidation by DMD with the Jacobsen catalyst.

Syntheses and transformations of α-azido ketones and related derivatives

Organic azides are known and utilized in the synthetic organic chemistry as amine precursors, potential sources of nitrenes, dipoles useful in 1,3-dipolar cycloadditions and starting materials of phosphoranes for a long time, and their literature has been overviewed by several authors. On the other hand, there are some special subclasses within the azides which possess peculiar and interesting properties differing from those of the majority and offering extra synthetic possibilities. In this critical review we wish to give an exhaustive overview on the synthesis and synthetic potential of α-azido ketones and related systems, an underestimated group of compounds. The enhanced acidity of the α-hydrogen offers various new synthetic applications including the creation of a new C-C bond, while the joint presence of the carbonyl and vinyl functions of α-azido-α,β-unsaturated ketones results in a special reactivity, too. Chemo- and stereoselectivity issues also represent important points which are discussed in detail. Finally, the usefulness of the titled derivatives in the synthesis of various heterocycles is reviewed (273 references).

Base‐Induced Coupling of α‐Azido Ketones with Aldehydes − An Easy and Efficient Route to Trifunctionalized Synthons 2‐Azido‐3‐hydroxy Ketones, 2‐Acylaziridines, and 2‐Acylspiroaziridines

An improved synthesis of α-azido ketones under phase-transfer conditions has been developed. The transformation of α-azido ketones into acyclic and heterocyclic 2-azido-3-hydroxy ketones has been demonstrated and the relative configurations of the chromanone derivatives have been determined by X-ray analysis. Treatment of the aldol-type products with triphenylphosphane afforded 2-acylaziridines and the hitherto unknown spiro[chroman-3,2′-aziridin]-4-ones. The relative configuration of the spiroaziridines was determined by NOE measurements.

Synthesis of variously coupled conjugates of d-glucose, 1,3,4-oxadiazole, and 1,2,3-triazole for inhibition of glycogen phosphorylase

5-(O-Perbenzoylated-β-D-glucopyranosyl)tetrazole was obtained from O-perbenzoylated-β-D-glucopyranosyl cyanide by Bu(3)SnN(3) or Me(3)SiN(3)-Bu(2)SnO. This tetrazole was transformed into 5-ethynyl- as well as 5-chloromethyl-2-(O-perbenzoylated-β-D-glucopyranosyl)-1,3,4-oxadiazoles by acylation with propiolic acid-DCC or chloroacetyl chloride, respectively. The chloromethyl oxadiazole gave the corresponding azidomethyl derivative on treatment with NaN(3). These compounds were reacted with several alkynes and azides under Cu(I) catalysed cycloaddition conditions to give, after removal of the protecting groups by the Zemplén protocol, β-D-glucopyranosyl-1,3,4-oxadiazolyl-1,2,3-triazole, β-D-glucopyranosyl-1,2,3-triazolyl-1,3,4-oxadiazole, and β-D-glucopyranosyl-1,3,4-oxadiazolylmethyl-1,2,3-triazole type compounds. 5-Phenyltetrazole was also transformed under the above conditions into a series of aryl-1,3,4-oxadiazolyl-1,2,3-triazoles, aryl-1,2,3-triazolyl-1,3,4-oxadiazoles, and aryl-1,3,4-oxadiazolylmethyl-1,2,3-triazoles. The new compounds were assayed against rabbit muscle glycogen phosphorylase b and the best inhibitors had inhibition constants in the upper micromolar range (2-phenyl-5-[1-(β-D-glucopyranosyl)-1,2,3-triazol-4-yl]-1,3,4-oxadiazole 36: K(i)=854μM, 2-(β-D-glucopyranosyl)-5-[1-(naphthalen-2-yl)-1,2,3-triazol-4-yl]-1,3,4-oxadiazole 47: K(i)=745μM).

Highly diastereoselective Michael reaction under solvent-free conditions using microwaves: conjugate addition of flavanone to its chalcone precursor

Microwave-assisted reaction of 2′-hydroxychalcones in the presence of DBU resulted in the formation of hitherto unknown dimers by conjugate addition of the intermediate cyclic ketone to the starting enone.

Enantioselective synthesis and chiroptical properties of optically active isoflavone epoxides

Abstract Enantioselective epoxidation of isoflavones 1a-f has been performed by using Mn(III)salen complexes (R,R)- 3 and (S,S)- 3 as catalysts and dimethyldioxirane (DMD) or NaOCl together with 4-phenylpyridine N-oxide (PPNO) axial ligand as oxygen donors to obtain nonracemic isoflavone epoxides 2a-f. With the help of circular dichroism (CD) spectra of three enantiomeric pairs, and Snatzkes inverse octant rule, the absolute configurations of these optically active isoflavone epoxides have been determined.

Enantioselective epoxidation of isoflavones by Jacobsen's Mn(III)salen catalysts and dimethyldioxirane oxygen-atom source

Abstract The catalytic enantioselective epoxidation of the isoflavones 1a–f has been performed by the Mn(III)salen complexes (R,R)-3 and (S,S)-3 as catalysts and dimethyldioxirane as the oxygen-atom source to afford optically active isoflavone epoxides 2a–f. The absolute configuration of the nonracemic epoxides 2 have been determined by X-ray diffraction analysis. Our present results constitute the first examples of the preparation of optically active isoflavone epoxides.

DIOXIRANE OXIDATION OF (Z)-1-THIOAURONES, (E)-3-ARYLIDENE-1-THIOCHROMAN-4-ONES AND (E)-3-ARYLIDENE-1-THIOFLAVAN-4-ONES

Abstract The oxidation of the title compounds 1, 4 and 7 with dimethyldioxirane (DMD) afforded the corresponding sulfoxides 2, 5 and 8 and/or sulfones 3, 6 and 9 in good yields (Scheme 1 and 2). Excess dimethyldioxirane gave the sulfones chemoselectively without formation of the epoxides. The epoxidation of the sulfones 6a,b,d to the respective spiroepoxides 10a,b,d required the more reactive methyl(trifluoromethyl)dioxirane (TFD) as oxidant.

Amino acid ligand chirality for enantioselective syntheses

Amino acids are attractive sources of chirality in stoichiometric or catalytic transition metal/organic chemistry. In spite of easy availability and other advantages, the application of these ligands is hindered by several problems. Now, at the dawn of emerging d‐amino acid biochemistry, efforts in this direction are becoming increasingly important. The results of research on application of amino acid ligands for transition‐metal reagents in organic syntheses are reviewed in the present work.

Efficient Synthesis of Chromones with Alkenyl Functionalities by the Heck Reaction

The usefulness of the Heck reaction in the field of chromones has been demonstrated. Bromochromones with the halogen atom in their rings A and B were reacted with various terminal alkenes to give hitherto unknown alkenyl‐substituted chromones. Reactivity of the substrates was found to markedly depend on the position of the bromine atom. Under phosphine‐free conditions using a phase‐transfer catalyst additive (tetrabutylammonium bromide), shorter reaction periods and usually higher yields were obtained.