Cyclocondensation reaction of 4-aryl-4-methoxy-1,1,1-trifluoro-3-buten-2-ones with urea: Synthesis of novel 6-aryl(5-methyl)-4-trifluoromethyl-2(1H)-pyrimidinones

The synthesis of a novel series of eleven 6-aryl(5-methyl)-4-trifluoromethyl-2(1H)-pyrimidinones, where aryl=Ph, 4-CH₃Ph, 4-FPh, 4-ClPh, 4-BrPh, 4-OCH₃Ph and alkyl=H, CH₃, from the reaction of 4-aryl-4-methoxy-1,1,1-trifluoro-3-buten-2-ones with urea in the presence of hydrochloric acid, is reported. Trifluoroacetylation of acetophenone- and propiophenone-dimethylacetals derived from phenones, was employed to obtain the precursors.     

Synthesis of the FG ring fragment of pectenotoxins 1-9

The synthesis of the FG ring fragment common to pectenotoxins 1-9 is reported. The successful, convergent synthesis relied on high yielding routes to access two key intermediates; aldehyde 1 and phosphonium salt 2. A Z-selective Wittig reaction gave access to advanced linear precursor 3, which was converted to FG ring fragment 4 using two sequential cyclization reactions.     

Disparate orientation of [1]rotaxanes

A novel [1]rotaxane 2 has been synthesized employing a 4-methyl-benzenesulfonyl and an azobenzene modified β-cyclodextrin (β-CyD) at the 2 position, through self-inclusion complexation and Suzuki-coupling capping in aqueous solution. Disparate absorption, induced circular dichroism (ICD) properties from its isomer [1]rotaxane 1, prepared from the isomeric β-CyD modifier at the 6 position, and the photoisomerization of [1]rotaxane 2 were thoroughly investigated.     

Stereoselective synthesis of trifluoromethylated vinyl- and dienylphosphonates with γ-alkoxycarbonyl moiety

Trifluoromethylated vinyl- and dienylphosphonates with γ-alkoxycarbonyl moiety have been synthesized via sequential transformations of bisphosphonates in 68-76% (three steps) yields with Z-isomers exclusively or predominantly.     

Convergent procedure for the synthesis of trifluoromethyl-containing N-(pyridinyl-triazolyl)pyrimidin-2-amines

This study describes a simple and efficient procedure to synthesize a novel series of fourteen 4-substituted N-(5-pyridinyl-1H-1,2,4-triazol-3-yl)-6-(trifluoromethyl)pyrimidin-2-amines, where the 4-substituents are H, CH₃, C₆H₅, 4-FC₆H₄, 4-CH₃C₆H₄, 4-CH₃OC₆H₄ and 2-Furyl; from the cyclocondensation reaction of N-[5-(pyridinyl)-1H-1,2,4-triazol-3-yl]guanidines with 4-alkoxy-4-alkyl(aryl/heteroaryl)-1,1,1-trifluoroalk-3-en-2-ones. The reactions were carried out in ethanol under reflux for 18 h and led to 40-68% yields. N-(Pyridyl-triazolyl)guanidine precursors were further obtained from reactions of cyanoguanidine with nicotinic or isonicotinic acid hydrazides and the halogenated enones from trifluoroacetylation of enolethers or acetals.     

Stereodivergent synthesis of the 2,3,5,6-tetrasubstituted piperidine ring system: an application to the synthesis of alkaloids 223A and 205B from poison frogs

Stereodivergent synthesis of the 2,3,5,6-tetrasubstituted piperidine ring system has been achieved by sequential stereocontrolled Michael-type conjugate addition reaction of appropriate enaminoesters. This methodology has been applied to the total syntheses of the poison frog alkaloids 223A and 205B. The relative stereochemistry of natural 223A at the 6-position was revised, and the absolute stereochemistry of natural 205B was determined by the present synthesis.     

First stereoselective total synthesis of decytospolides A and B

The first stereoselective total synthesis of decytospolides A and B has been accomplished starting from n-hexanal. The key steps involved in this synthesis are Horner-Wittig reaction, Sharpless asymmetric epoxidation, and oxa-Michael reaction.     

A convenient synthesis of l-ribose from d-fructose

An efficient method for the stereoselective synthesis of l-ribose was accomplished starting from commercially inexpensive d-fructose. The intermediates in the process can serve as versatile precursors for the preparation of l-nucleoside analogues.     

A highly efficient synthesis of 22-deoxy-OSW-1 by utilizing the intact skeleton of diosgenin

22-Deoxy-OSW-1 (1), an analogue of OSW-1 with the potent anticancer activity, was synthesized by utilizing the intact skeleton of diosgenin in 11 steps in 13.7% overall yield. This synthesis demonstrated an effective and reasonable synthetic strategy for bioactive steroids with side chains.     

Five-membered heterocycles. Part III. Aromaticity of 1,3-imidazole in 5+n hetero-bicyclic molecules

The aromaticity (in the form of HOMA index) of 1,3-imidazole ring and its bicyclic derivatives was studied on the basis of statistical data from Cambridge Structural Database and X-ray investigations performed by authors. As a starting point, aromaticity of the 1,3-imidazoles with exocyclic X substituent at C2 (XN, O or S) was calculated. Subsequently, the HOMA index was calculated for various 5+n bicyclic skeletons with N, O, and S as endocyclic heteroatoms in the second ring. For the isolated 1,3-imidazole ring, aromaticity depends on exocyclic substituent at C2 and decreases in sequence N, S, O. For bicyclic derivatives it was found that both rings are aromatic and coplanar in very few molecules (17% of investigated ones), and positive charge—located on endocyclic heteroatom—increases the aromaticity. For remaining compounds, presence of sp³ carbons excludes possibility of aromatic ring existence.     

Enantiodivergent synthesis of the quinolizidine poison frog alkaloid 195C

Herein, we describe the enantiodivergent synthesis of the 1,4-cis-disubstituted quinolizidine alkaloid 195C. Although the stereoselectivity of the final hydrogenation reaction was low, we have proposed the first chiral total synthesis of both (−)- and (+)-195C as an enantiodivergent process.     

A convenient synthesis of 2-C-methyl-d-erythritol 4-phosphate and isotopomers of its precursor

A new synthetic approach toward 2-C-methyl-d-erythritol 4-phosphate (MEP), a key intermediate in the mevalonate-independent biosynthetic pathway for isoprenoids, and deuterated analogues of its precursor, 2-C-methyl-d-erythritol acetonide, is described. This procedure uses 2-C-methyl-d-erythrose acetonide as starting material and delivers, through a mono-protection strategy, the target compounds in a short way and in high yield.     

Haloacetylated enol ethers: 18 : Synthesis of alkyl 6-[azol-3(5)-yl]hexanoates

A convenient method for the synthesis of eight alkyl 6-[4,5-dihydroisoxazol-3-yl(-pyrazol-3(5)-yl)]hexanoates from the cyclocondensation of methyl 10,10,10-trifluoro[chloro]-9-oxo-7-methoxydec-7-enoates and hydroxylamine hydrochloride or hydrazine hydrochloride, respectively, in ethanol as solvent is reported. The reaction of methyl 10,10,10-trichloro-9-oxo-7-methoxydec-7-enoates with hydrazines furnished the pyrazole derivatives with the simultaneous transformation of trichloromethyl to carboxyl group.     

Polyhalogenoheterocyclic compounds: Part 54: [1] Suzuki reactions of 2,4,6-tribromo-3,5-difluoropyridine

Palladium catalysed Suzuki cross-coupling reactions between 2,4,6-tribromo-3,5-difluoropyridine and a short series of aromatic boronic acid derivatives gave 4-bromo-3,5-difluoro-2,6-diphenylpyridine derivatives arising from displacement of bromine atoms attached to positions ortho to ring nitrogen or the corresponding triaryl systems depending on the reaction conditions. Consequently, the use of polybromofluoropyridine scaffolds for the synthesis of polyfunctional heteroaromatic derivatives is expanded further.     

A convenient, large-scale synthesis of 4′-carboxamido N-Boc-2′,6′-dimethyl-l-phenylalanines

A large-scale synthesis of a series of 4′-carboxamido N-Boc-2′,6′-dimethyl-l-phenylalanines is described. This method features mild reaction conditions and high chemical yields from commercially available N-Boc-2′,6′-dimethyl-l-tyrosine methyl ester.     

I2 as an efficient catalyst in ionic Diels-Alder reactions of α,β-unsaturated acetals

A variety of protected and unprotected α,β-unsaturated aldehydes react with 1,3-dienes in the presence of I₂ to give the corresponding cycloadducts.     

Solid-phase synthesis of traceless 1,3-diketones

A traceless synthesis of 1,3-diketones has been achieved through enamine methodology from solid-phase organic synthesis. Thus, piperazine served as a linker for this traceless cleavage of β-diketones from solid support.     

First enantioselective synthesis of (+)-quinolizidine 207I: determination of the absolute stereochemistry

First enantioselective synthesis of quinolizidine 207I has been achieved and the absolute stereochemistry of natural quinolizidine 207I was determined to be 1S,4S,10S by the present chiral synthesis using GC analysis with β-dextrin chiral column on co-injection with racemate.