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A protocol for synthesizing triazole-containing pyrazolines and pyrazoles selectively using trifluoromethylated 5-(1,2,3-triazol-1-yl)enones as starting materials, is reported. The selectivity of the reaction was controlled by the nature of the hydrazine or derivative used: free hydrazines furnished the 1,5-regiosiomer exclusively in yields up to 98%, whereas protected hydrazines provided the 1,3-regioisomer in yields up to 77%. To demonstrate the synthetic versatility of the triazole-based enone, reactions with other unsymmetrical dinucleophiles (hydroxylamine hydrochloride and S-methyl isothiourea sulfates) allowed the selective preparation of triazole-containing isoxazoline and pyrimidine rings.

In this work, the reactivity of 5-bromo-1,1,1-trifluoro-4-methoxypent-3-en-2-one toward primary aliphatic amines was studied. The reaction was found to be extremely selective to synthesize a series of 1-alkyl-4-(aminoalkyl)-2-(trifluoromethyl)-1H-pyrroles (13 examples, up to 90% yield) and a series of highly functionalized β-enaminones (6 examples, up to 78% yield), with only the amount of amine and the reaction conditions needing to be controlled. The structure of the products was unambiguously determined by single crystal X-ray diffraction and 2D NMR experiments.

The regioselective synthesis of twenty novel [3-substituted 5-hydroxy-5-(trifluoromethyl)-4,5-dihydro-1H-pyrazol-1-yl][6-aryl-(2-methylthio)pyrimidin-4-yl]methanones from the cyclocondensation reactions of new 6-aryl-2-(methylthio)pyrimidine-4-carbohydrazides with 4-substituted 1,1,1-trifluorobut-3-en-2-ones is reported. Human acetylcholinesterase (HsAChE) and butyrylcholinesterase (HsBChE) inhibition tests were performed on selected products in order to explore the possible pharmacological applications of these compounds. Two compounds showed significant and selective inhibitory activity for BChE.

The 1,4-dicarbonyl scaffold ethyl 3-formyl-4,5-dihydrofuran-2-carboxylate was obtained through the rearrangement of the parent ethyl 2-(4,5-dihydrofuran-3-yl)-2-oxoacetate and applied to the synthesis of a series of 7-alkoxy-2,3-dihydrofuro[2,3-d]pyridazines. Twelve pyridazines­ were obtained in yields of up to 70%.

5-Bromo- and 5,5-dibromo-1,1,1-trihalo-4-methoxypent-3-en-2-ones (brominated enones) have proven to be attractive building blocks for the construction of heterocyclic and polyheterocyclic compounds bearing a trihalomethyl moiety through interesting cyclocondensation, alkylation, and cycloaddition reactions. This review compiles all of the reactions conducted with these brominated enones since they were first disclosed in 2001.1 Introduction2 Synthesis and Initial Applications3 Synthesis Using First-Generation Intermediates4 Synthesis Using Second-Generation Intermediates5 Synthesis Using Third-Generation Intermediates6 Conclusions

The use of β-enamino diketones as an easy entry to the regioselective synthesis of [1,2,4]triazolo[1,5-a]pyrimidines is reported. These ketones reacted with 3-amino-1H-1,2,4-triazoles to furnish exclusively 6-substituted 5-(trifluoromethyl)[1,2,4]triazolo[1,5-a]pyrimidines in yields of up to 95%. The regioselectivity of the reactions performed was maintained regardless of the substituent in the starting ketone or aminoazole.

The synthetic versatility of 4-alkoxy-4-alkyl/aryl-1,1,1-trichloroalk-3-en-2-ones (enones) for the synthesis of [1,2,4]triazolo[1,5-a]pyrimidines, in which the trichloromethyl group is either maintained or eliminated from the product by simply controlling the reaction medium, is reported. These enones react with 3-amino-1H-1,2,4-triazoles under acidic conditions to furnish exclusively 7-(trichloromethyl)-[1,2,4]triazolo[1,5-a]pyrimidines, whereas under basic conditions [1,2,4]triazolo[1,5-a]pyrimidin-5/7(1H)-ones are obtained with elimination of the trichloromethyl group. The regioselectivity of the reactions performed under basic conditions is highly influenced by the substituents present in the starting enones. Twenty-one examples are synthesized using these two methodologies, with yields of up to 86%.

Three new series of compounds, 5-alkoxy-3-(trifluoromethyl)penta-2,4-dienenitriles, 5-(phenylthio)-3-(trifluoromethyl)penta-2,4-dienenitriles, and ethyl 4-alkoxy-2-(cyanomethylene)but-3-enoates, obtained from the olefination reaction of the respective enones with diethyl cyanomethylphosphonate via the Horner–Wadsworth–Emmons olefination are reported. All products were obtained as single regioisomers; however, the composition of the stereoisomers changed according to the enone substituents. A study based on 1H and 13C NMR chemical shifts, 1H–19F and 13C–19F NMR coupling constants, 1H NMR signal integrals, and HSQC, HMBC, and NOESY experiments was performed in order to assign the structure and percentage of each stereoisomer obtained.

This study reports a simple and highly regioselective synthesis of a new series of 3,6-disubstituted 2-(methylsulfanyl)pyrimidin-4(3H)-ones, in which the 6-substituents are methyl or aryl groups and the 3-substituents are alkyl, allyl, phenyl, benzyl, or 2-phenylethyl groups. The products are obtained in good yields by cyclocondensation of the appropriate 4-substituted 4-methoxy-1,1,1-trichloroalk-3-en-2-ones with nonsymmetric 1-substituted 2-methylisothiourea sulfates under mild basic conditions.

Metal-free electrophilic fluorination, promoted by Selectfluor, of pyrazoles with methylene groups (CH2X), in which X = OH, OMe, F, N3, and NHMe at the C-4 position furnished the 4-fluoro-pyrazole products from unexpected C–C bond cleavage, at moderate to good yields. Otherwise, under the same reaction conditions, when X = NEt2 or SPr, the oxidation product 4-formyl-pyrazole was obtained.

A simple and efficient procedure for the synthesis of ethyl 2-methylthio- and ethyl 2-benzylthio-6-methyl(aryl)-pyrimidine-4-carboxylates and their corresponding acid derivatives is reported. The products are obtained in good yields via the cyclocondensation reaction of ethyl 4-alkoxy-2-oxo-4-methyl(aryl)-but-3-enoates with 2-meth­ylisothiourea sulfate or 2-benzylisothiourea hydrochloride, under mild, basic, aqueous conditions.

This study describes an improved one-pot, four-step synthesis­ of a new series of 1-aryl-3-trifluoroacetyl pyrroles from the reaction of 3-trifluoroacetyl-4,5-dihydrofuran with arylamines, giving 1,1,1-trifluoro-3-(2-hydroxyethyl)-4-arylamino-3-buten-2-ones, which were directly submitted to Swern oxidation to furnish 1,1,1-trifluoro-3-(2-ethanal)-4-arylamino-3-buten-2-ones. Subsequent intramolecular cyclization of the corresponding enaminoaldehydes followed by aromatization rendered the title compounds in a 30 to 56% overall yield.

A simple and efficient one-pot synthesis of tetrahydrooxazolo[3,2-a]pyridines and hexahydroimidazo[1,2-a]pyridines, and some related oxa- and aza-condensed tetrahydropyridines, from the reaction of 2-alkoxy-5-(trifluoroacetyl)-2,3-dihydro-2H-pyrans (cyclic enones) with amino alcohols and primary diamines, is reported. Products were isolated with high purity and in very good yields.

A new one-pot strategy for the synthesis of a series of new N-substituted 3-trifluoroacetyl pyrroles is presented. These compounds were obtained by the reaction of 3-trifluoroacetyl-4,5-dihydrofuran with primary amines, which generated 1,1,1-trifluoro-3-(2-hydroxyethyl)-4-alkylaminobut-3-en-2-one intermediates. In most cases these intermediates were not stable enough to be isolated. Thus, in the same reaction vessel they were directly submitted to oxidation with PCC (Corey's reagent) to furnish 1,1,1-trifluoro-3-(2-ethanal)-4-alkylaminobut-3-en-2-ones, which under reflux underwent intramolecular cyclization to give the desired N-substituted 3-trifluoroacetyl pyrroles, in moderate yields. All of these pyrroles were tested against pan-susceptible Mycobacterium tuberculosis H37Rv and clinical isolates INH- and RMP-resistant strain and some of these compounds showed significant in vitro antimicrobial activity.

The reaction of unsymmetrical enamino diketones [RC(O)C(=CNMe 2 )C(O)CO 2 Et,where R = Ph, 4-MeC 6 H 4 ,4-MeOC 6 H 4 , 4-BrC 6 H 4 ,4-ClC 6 H 4 , 4-FC 6 H 4 , 4-O 2 NC 6 H 4 ,2-thienyl, benzofuran-2-yl, and CF 3 ] with N-C-Ndinucleophiles, such as benzamidine hydrochloride or 1 H-pyrazole-1-carboxamidine monohydrochloride,afforded a series of ethyl 2,5-disubstituted pyrimidine-4-carboxylatesin a chemoselective and highly chemo-selective manner (51-86%).Reaction of these two series of pyrimidines (R = Ph,4-MeOC 6 H 4 , 4-FC 6 H 4 ,and 2-thienyl) with hydrazine monohydrate under mild conditionsled to 2,5-substituted pyrimido[4,5- D]pyridazin-8(7 H)-ones in high yields (81-92%).

Three methods for the regiospecific bromination of 2-pnenyl-3H-pyrimidin-4-ones are presented: bromination or the 5-position of the pyrimidine ring, bromination of the 6-benzylic position and simultaneous bromination of both the 5-position of the pyrimidine ring and 6-benzylic position. Reactions were carried out using simple protocols and the brominated pyrimidines were obtained in good yields.

A series of 4-substituted 1 H-pyrazole-5-carboxylates was prepared from the cyclocondensation reaction of unsymmetrical enaminodiketones [RC(O)C(=CNMe 2 )C(O)CO 2 Et, where R = Ph, 4-MeOC 6 H 4 , 4-ClC 6 H 4 , 4-FC 6 H 4 , 4-O 2 NC 6 H 4 , thien-2-yl, benzofur-2-yl, CCl 3 and CF 3 ] with TERT-butylhydrazine hydrochloride or carboxymethylhydrazine. The compounds were obtained regiospecifically and in good to excellent yields (73-94%). In addition, 5-carboxyethyl-1-(1,1-dimethylethyl)-1 H-pyrazole-4-carboxylic acid was synthesized from regiospecific conversion of ethyl 4-(2,2,2-trichloroacetyl)-1-(1,1-dimethylethyl)-1 H-pyrazole-5-carboxylate. The carbonyl substitution reaction was regiospecific for the trichloroacetyl group and did not affect the ester group.

The acylation reaction of secondary (R 1 = H) β-enamino ketones [RCOCH=CHNR 1 R 2 , where R = CF 3 , CCl 3 , Ph, 4-FC 6 H 4 , 4-NO 2 C 6 H 4 , thien-2-yl; R 1 = H, Me; R 2 = Me, Bn, Ph, 4-NO 2 C 6 H 4 ] with trifluoroacetic anhydride or ethyl oxalyl chloride in pyridine led regiospecifically to a series of 14 N-acylated enaminones in good yields (72-88%). On the other hand, when tertiary enaminones (R 1 , R 2 = Me) were used, the acylation reaction led to a series of 12 C-acylated enaminones in good to excellent yields (75-92%).

The synthesis of some potentially active 2-(trifluoro-methyl)pyrimido[1,2-a]benzimidazoles and pyrimido[1,2-a]benzimidazol-2(1H)-ones by the cyclization of 4-alkoxyvinyl trifluoro(chloro)methyl ketones with 2-aminobenzimidazole is described. The structure of the products was assigned based on 'H and 13 C NMR as well as 2D-NMR experiments. Some of the obtained products exhibited significant DNA-topoisomerase I inhibitory activity.

A convenient method to obtain 10 3-amino-5-trifluorom-ethyl-5-hydroxy-4,5-dihydroisoxazoles and 18 3-amino-5-trifluoromethyl-lH-pyrazoles by cyclocondensation reaction of 4-amino-4-ethoxy-1,1,1,-trifluorobut-3-en-2-ones [CF3COCH=C(OEt)NHR, where R=H, Me, Et, CH 2 CH 2 OH, CMe 2 Et, CH 2 Ph, Ph, 4-NH 2 C 6 H 4 , 4-ACC 6 H 4 , 4-NO 2 C 6 H 4 , 5-methylisoxazol-3-yl, thiazol-2-yl, CH 2 CO 2 Et, CH(Ph)CO 2 Me, CH(i-Bu)CO 2 Et] with hydroxylamine, hydrazine and phenylhydrazine is reported.

Heterocyclization of 1,1,1-trifluoro[chloro]-4-methoxy-4-[2-tienyl]-3-buten-2-one and 1,1,1-trifluoro[chloro]-4-methoxy-4-[2-furyl]-3-buten-2-ones into isoxazoles and pyrazoles derivatives as a new type of trihalomethylated bicyclic heterocycles is reported.

Reaction of 4-trichloromethyl-1H-pyrimidin-2-ones with 5-bromo-1,1,1-trichloro(fluoro)-4-methoxy-alk-3-en-2-ones affords 1-(5,5,5-trichloro(fluoro)-2-methoxy-4-oxopent-2-en-1- yl)-4-trichloromethyl-1H-pyrimidin-2-ones. Reaction of the latter trichloromethylated compound with amines, hydroxylamine, and hydrazines affords a series of 1-(2-alkylamine-5,5,5-trichloro-4- oxopent-2-en-1-yl)-4-trichloromethyl-1H-pyrimidin-2-ones and 1-(5-trichloromethyl-5-hydroxy-4,5-dihydro-3-azol-3-ylmethyl)-4- trichloromethyl-1H-pyrimidin-2-ones, respectively.

The regiospecific synthesis of a novel series of 4-trifluoro[chloro]-2-(5-hydroxy-5-trifluoro[chloro]methyl-4,5-dihydro-1H-pyrazol-l-y1]-pyrimidines from the reactions of 4-alkoxy-1,1,1 -trifluoro[chloro]-alk-3-en-2-ones with 6-trifluoro(chloro]methyl-2-hydrazine pyrimidines is presented.

The synthesis of 1,1,1-trichloro-4,4-diethoxy-3-buten-2-one and three trichloroacetylacetate derivatives from the acylation reaction of respective trialkyl orthoacetates and orthopropionates with trichloroacetyl chloride in good yields, is reported. The title compounds were used for the regiospecific preparation of two isoxazoles and five pyrazoles in the cyclocondensation with hydroxylamine and hydrazines, respectively. The transformation of the trichloromethyl group under mild conditions into carboxylic groups is also described.

A convenient selective protection of the u-amino carboxyl group of amino acids bearing reactive side chain groups such as arginine, asparagine, glutamine, cysteine, histidine, serine and lysine, using 4-alkoxy-1,1,1-trifluoro[chloro]alk-3-en-2-ones is reported. The reactions were performed without esterification of the carboxyl group and N-deprotection was carried out using a six molar solution of hydrochloric acid.

The synthesis of a new series of 3-alkosy-5-hydmxy-5-trifluoromethyl pyrriolidin-2-ones 2a-h from the reaction of 1,1,1-trifluoro-4-alkoxyalk-3-en-2-ones la-h of the general formula F 3 CC(O)C(R 2 )=C(R 1 )OR. where: R=Me, Et, -(CH 2 ) 2 -, -(CH 2 ) 3 -; R 1 = H. Me, Ph, p-Me-Ph, p-F-Ph: and R 2 = H, Me, -(CH 2 ) 2 -, -(CH 2 ) 3 - with sodium cyanide in hydro-alcoholic medium is reported.