Alex F. C. Flores

Efficient sonochemical synthesis of novel 3,5-diaryl-4,5-dihydro-1H-pyrazole-1-carboximidamides

An ultrasound-assisted preparation of a series of novel 3,5-diaryl-4,5-dihydro-1H-pyrazole-1-carboximidamides that proceeds via the efficient reaction of chalcones with aminoguanidine hydrochloride under clean conditions is described.

Synthesis of 1,1,1-trihalo-4-methoxy-4-[2-heteroaryl]-3-buten-2-ones, the corresponding butan-1,3-dione and azole derivatives

The synthesis of 1,1,1-trihalo-4-methoxy-4-[2-thienyl]-3-buten-2-ones, 1,1,1-trihalo-4-methoxy-4-[2-furyl]-3-buten-2-ones and the respective trihalomethyl 1,3-butanone derivatives by trihaloacylation of dimethoxy acetals derived from 2-acetylthiophene and 2-acetylfuran are reported. This is a convenient method to obtain fluorinated and chlorinated 1,3-dielectrophiles from 2-acetylthiophene and 2-acetylfuran. The fluorinated 1,3-dielectrophiles were used to synthesize five new 2-thienyl- and 2-furylazoles. The structure of all products were assigned by 1HH- and 13C NMR and mass spectrometry.

Regiospecific acylation of acetals. A convenient method to obtain β-methoxyvinyl trichloromethyl ketones

Abstract The regiochemistry of the acylation of enol ethers, generated in situ, from acetals of unsymmetrical ketones is reported. These results demonstrate a convenient one-pot method to obtain a series of β-methoxyvinyl trichloromethyl ketones [CCl 3 COCHC(OMe)R, where R=Et, n -Bu, i -Pr, (CH 2 ) 2 C(OMe)CHC(O)CCl 3 and (CH 2 ) 5 CO 2 CH 3 )] in high yields.

A convenient one-pot synthesis of 5-carboxyisoxazoles: trichloromethyl group as a carboxyl group precursor

Abstract The one-pot synthesis of ten 5-carboxyisoxazoles from the cyclocondensation of β-alkoxyvinyl trichloromethyl ketones [CCl 3 C(O)C(R 2 )C(R 1 )OR, where R 1 , R 2 =H, Me and R=Me, Et] and 2-trichloroacetyl cyclohexanone with hydroxylamine is reported. This work shows that the trichloromethyl group attached to β-alkoxyvinyl trichloromethyl ketones (a heterocyclic CCC building block) is an excellent carboxyl group precursor.

Environmentally friendly sonocatalysis promoted preparation of 1-thiocarbamoyl-3,5-diaryl-4,5-dihydro-1H-pyrazoles

An efficient and green synthesis of thiocarbamoyl-3,5-diaryl-4,5-dihydro-1H-pyrazoles via the condensation of chalcones with thiosemicarbazide in ethanol and KOH under ultrasound irradiation is reported. The products were isolated in good yields after short reaction times.

Ultrasound promoted synthesis of thioesters from 2-mercaptobenzoxa(thia)zoles

An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields.

Phosphorus Forms and Availability Assessed by 31P‐NMR in Successively Cropped Soil

Abstract Soils under no‐tillage gradually increase in organic matter and phosphorus (P) content from the top layer. Because of lack of knowledge about the organic phosphorus fraction contribution to plant nutrition, this research was conducted to estimate the availability of phosphorus fractions to plants. Soil samples of a very clayey Rhodic Hapludox that received 0, 156 and 312 kg P ha−1 were submitted to 15 successive crops in pots without replacing P extracted by plants. 31P nuclear magnetic resonance analysis was performed to detect P fractions before cultivation and after the sixth, ninth and fifteenth crops. Inorganic phosphorus was the unique P fraction acting as P source to plants in soils with previous P addition. Contribution of organic P was observed only when inorganic P content was extremely low, with plants showing severe P stress. Contribution of organic P was not enough to supply the required P for normal plant growth.

Synthesis of hydroxypyrazoles and 1-methyl-3-isoxazolones via haloform reactions

Abstract The synthesis of a new series of hydroxypyrazoles ( 2a – f ) and 2-methyl-3-isoxazolones ( 3a – d ) from the cyclocondensation reaction of trichloromethyl-substituted 1,3-dielectrophiles ( 1a – f ) with dry hydrazine and N -methylhydroxylamine is reported. The regiospecific cyclocondensation took place with the elimination of the trichloromethyl group in a haloform type reaction when acetonitrile under basic medium was used. The structure of compounds 2 and 3 were determined mainly by 1 H and 13 C NMR spectroscopy.

HALOACETYLATED ENOL ETHERS: 16[5] REGIOSPECIFIC SYNTHESIS OF 5-TRICHLOROMETHYL-PYRAZOLES

ABSTRACT The regiospecific synthesis and isolation of three series of 5-trichloromethyl-pyrazoles 2f–j, 3a–j and 4a–j from the cyclocondensation of 1,1,1-trichloro-4-alkoxy-3-alken-2-ones (1a–f) or trichloroacetyl containing β-diketones (1g–j) with dry hydrazine and phenyl-hydrazine is reported. It was established by 1H- and 13C-NMR spectroscopy that the 5-hydroxy-5-trichloromethyl-4,5-dihydro-1H-pyrazole intermediates 2a–j were formed quantitatively.

β-Alkoxyvinyl trichloromethyl ketones as N-heterocyclic acylating agent. A new access to 5H-thiazolo[3,2-a]pyrimidin-5-ones

Abstract Using trichloromethyl substituent as convenient leaving group for the synthesis of interesting bi-heterocyclic compounds, a series of 6-methyl- and 7-alkyl(aryl)-5 H -thiazolo[3,2- a ]pyrimidin-5-ones, where alkyl=methyl, n -propyl, isopropyl, isobutyl, n -hexyl, isopentyl and aryl=phenyl, 4-toluyl, 4-chlorophenyl, 4-bromophenyl, 4-methoxyphenyl was obtained from a simple and regiospecific reaction of 4-alkoxy-1,1,1-trichloro-3-alken-2-ones with 2-aminothiazole in good yield (45–89%).