卷 54, 编号 6 (2018)

Amino acid-based catalysts have been intensively researched in recent years. Amino acid-derived phosphines possess high nucleophilicity and exhibit unique catalytic activities in asymmetric synthesis. L-Threonine and valine are most utilized natural amino acids in the preparation of chiral phosphines. The efficient and versatile chiral phosphine catalysts are applied in a wide range of reactions such as MBH reaction, Rauhut–Currier reaction, Michael addition, [4 + 2]-annulation, [3 + 2]-annulation, 1,4-dipolar cycloaddition. They are also widely used in the construction of core structures of natural products. Amino acid-based phosphine catalysts and their applications in asymmetric synthesis are summarized.

An efficient procedure has been developed for the synthesis of difficultly accessible 9,9′-(alkane-α,ω-diyl)bis[7-(diphenylmethylidene)bicyclo[4.2.1]nona-2,4-dienes] and 16,16′-(alkane-α,ω-diyl)bis(tricyclo-[9.4.1.0^2,10]hexa-2,12,14-trienes) in 55–84% yields by [6π + 2π]-cycloaddition of 7,7′-(alkane-α,ω-diyl)bis-(cyclohepta-1,3,5-trienes) to 1,1-diphenylpropa-1,2-diene and cyclonona-1,2-diene in the presence of the catalytic system Ti(acac)₂Cl₂–Et₂AlCl. The structure of the isolated compounds has been reliably proved by modern spectral methods.

Transformation of the nitromethyl group in 3-(2-aryl-3-nitropropyl)-6,6-dimethyl-6,7-dihydro-1,2-benzoxazol-4(5H)-ones by the Nef reaction gave the corresponding aldehydes. Jones oxidation of the latter afforded carboxylic acids together with oxidative decarboxylation products. The possibility for the construction of heterocyclic fragment on the basis of the formyl or carboxylmethyl group of the resulting 6,7-dihydro-1,2-benzoxazol-4(5H)-one derivatives was studied.

A new strategy has been proposed for the synthesis of 5H-[1]benzofuro[2,3-d][1,2]diazepines containing two aryl substituents in the diazepine fragment. The key stage of the synthesis is intramolecular cyclization of the corresponding hydrazides under the Bischler–Napieralski reaction conditions.

2-Chloropyridine-3,4-dicarbonitriles reacted with hydrazine hydrate in ethanol to give 2-hydrazinylpyridine- 3,4-dicarbonitriles. Condensation of the latter with salicylaldehyde and its substituted derivatives afforded the corresponding 2-{2-[2-hydroxyphenylmethylidene]hydrazinyl}pyridine-3,4-dicarbonitriles. The fluorescence spectra of the hydrazones obtained from 3-methoxysalicylaldehyde showed sensitivity toward zinc ions.

The condensation of various nonaromatic amines with ethyl N-{[4-(4-methoxyphenyl)tetrahydro-2H-pyran-4-yl]methyl}oxamate prepared from [4-(4-methoxyphenyl)tetrahydro-2H-pyran-4-yl]methanamine and diethyl oxalate afforded the corresponding N,N'-disubstituted oxamides. N-Aryloxamides were synthesized by the reaction of [4-(4-methoxyphenyl)tetrahydro-2H-pyran-4-yl]methanamine with ethyl N-aryloxamates. The condensation of N-{[4-(4-methoxyphenyl)tetrahydro-2H-pyran-4-yl]methyl}succinamic acid with primary amines gave N,N'-disubstituted siccinamides.

Dehydration of substituted 2-(2-oxopyrrolidin-1-yl)acetamides with phosphoryl chloride provides a convenient method of synthesis of 2-chloro-6,7-dihydro-5H-pyrrolo[1,2-a]imidazoles. The latter can be readily converted to various derivatives via introduction and modification of a substituent in the 3-position. The chlorine atom in the 2-position can be removed by hydrogenation over Raney nickel.

The reaction of 6-methylpyrimidine-2,41H,3H-dione with 2-chloromethylthiirane gave 6-methyl-N-thietan-3-ylpyrimidine-2,41H,3H-dione. Its oxidation subsequent reaction of the resulting N-1,1-dioxo-λ⁶-thietan-3-yl derivative with ethyl chloroacetate afforded the corresponding ethyl pyrimidinylacetate. The structure of the latter was determined by X-ray analysis, which confirmed the formation of N³-thietan-3-yl derivative rather than its N1-substituted isomer in the title reaction. According to the results of B3LYP/6-31G++d,p, PBE/3ζ, MP2/6-31G++d,p quantum chemical calculations,the N³-thietanyl derivative is more stable than the N¹-isomer. It was also found that the calculated barrier to internal rotation of the thietanyl group about the N–C bond in 6-methyl-3-thietan-3-yl-pyrimidine-2,41H,3H-dione is lower than in the N¹-isomer.

A new efficient method has been developed for the synthesis of highly biologically active pyrano-[4,3-d]pyrazolo[3,4-b]pyridines on the basis of Smiles rearrangement of ethyl [(8-alkyl(aryl)-5-cyano-3,3-dimethyl-3,4-dihydro-1H-pyrano[3,4-c]pyridin-6-yl)oxy]acetates. Intermediate acetohydrazides have also been isolated. The proposed procedure is advantageous due to the possibility of avoiding experimentally difficult chlorination stage.

Adenine derivatives with a phosphorus-containing substituent on N⁹ have been synthesized, and their structure has been confirmed by ¹H, ¹³C, and ³¹P NMR and IR spectroscopy, X-ray diffraction, MALDI mass spectrometry, and elemental analysis.

A preparative procedure has been proposed for the reduction of substituted nitroarenes with hydrazine hydrate in the presence of a nanocatalyst based on cobalt–nickel nanoparticles, which ensured selective formation of the corresponding anilines in 78–80% yield in 20–45 min.

Ethyl 1-aryl-4,5-dioxo-2-phenyl-4,5-dihydro-1H-pyrrole-3-carboxylates reacted with tetronic acid in boiling anhydrous toluene in the presence of acetic acid to give ethyl 1-aryl-4,4-bis(4-hydroxy-2-oxo-2,5-dihydrofuran-3-yl)-5-oxo-2-phenyl-4,5-dihydro-1H-pyrrole-3-carboxylates.

Heating of 4-aryl-N-(1H-pyrazol-4-yl)but-3-enamides in polyphosphoric acid selectively afforded 5-aryl-1-(1H-pyrazol-4-yl)pyrrolidin-2-ones.

Dichlorocarbene generated from chloroform in aqueous–alkaline medium in the presence of N-methylmorpholine N-oxide is converted to phosgene which reacts in situ with secondary amines to afford tetrasubstituted ureas.