Sulfur analogs of fluorinated pyrones, chromones and coumarins

This mini-review describes the synthesis and reactions of sulfur analogs of partially fluorinated pyrones, chromones, coumarins and isocoumarins and their utility as building blocks for the synthesis of trifluoromethyl-containing heterocyclic compounds with biological interest. © 2013 Copyright Taylor and Francis Group, LLC

A one-pot synthesis of tetrahydroisoquinolin-4-ols via a novel acid-catalyzed rearrangement of 5-aryloxazolidines

Benzaldehydes with electron-donating substituents react smoothly with a nonstabilized azomethine ylide derived from sarcosine and formaldehyde to form 5-aryloxazolidines as intermediates, which undergo rearrangement into 2-methyl-1,2,3,4-tetrahydroisoquinolin-4-ols in high yields by simple heating with hydrochloric acid. This one-pot synthesis of tetrahydroisoquinolines can be considered as a formal [3+3] cycloaddition of the azomethine ylide to the aromatic aldehyde. © 2013 Elsevier Ltd. All rights reserved

A simple two-step synthesis of 2-(alkylamino)-1-arylethanols, including racemic adrenaline, from aromatic aldehydes via 5-aryloxazolidines

Benzaldehydes react smoothly with nonstabilized azomethine ylides, generated in situ from sarcosine/formaldehyde or N-(methoxymethyl)-N- (trimethylsilylmethyl)benzylamine, to give 5-aryloxazolidines as intermediates. These were converted into 2-(alkylamino)-1-arylethanols in good yields by simple heating in methanol with hydrochloric acid, or by treatment with hydrazine hydrate in ethanol. © 2013 Elsevier Ltd. All rights reserved

Reaction of 5-aryloxazolidines with arylmagnesium bromides as a new route to N-benzyl-β-hydroxyphenethylamines as starting materials for the preparation of 4-aryl-1,2,3,4-tetrahydroisoquinolines

Benzaldehydes react smoothly with the non-stabilized azomethine ylide derived from sarcosine and formaldehyde to form 5-aryloxazolidines as intermediates, which undergo ring-opening to give N-benzyl-β- hydroxyphenethylamines in good yields by the action of arylmagnesium bromides. Their subsequent acid-catalyzed cyclization into 4-aryl-1,2,3,4- tetrahydroisoquinolines was performed in moderate to good yields. © 2013 Elsevier Ltd. All rights reserved

Synthesis of benzopyranopyrrolidines via 1,3-dipolar cycloaddition of nonstabilized azomethine ylides with 3-substituted coumarins

A three-component reaction of 3-substituted coumarins with N-alkyl-α-amino acids and aldehydes gave 1-benzopyrano[3,4-c]pyrrolidines as a result of a 1,3-dipolar cycloaddition of an intermediate nonstabilized azomethine ylide at the double bond of the coumarin system in moderate to good yields. In most cases, high regio- and stereo-selectivity of the [3+2] cycloaddition was observed. © 2013 Elsevier Ltd. All rights reserved

Synthesis of 6-(2-hydroxyaryl)-2-pyridones by the reaction of chromones with cyanoacetic, acetoacetic, and malonic acid amides

A reaction of chromones with cyanoacetic, acetoacetic, and malonic acid amides in the presence of sodium ethoxide furnished a number of new 3-substituted 6-(2-hydroxyaryl)-2-pyridones in good yields, including those containing a polyfluoroalkyl group at position 4. © 2013 Springer Science+Business Media New York

Synthesis of β-(trifluoromethyl)furans and spiro-gem- dichlorocyclopropanes from cyclic 1,3-dicarbonyl compounds and α-(trihaloethylidene)nitroethanes

While 1,3-dicarbonyl compounds react with (E)-1,1,1-trifluoro-3-nitrobut-2- ene in the presence of sodium acetate to produce the target β- (trifluoromethyl)furans, their reaction with (E)-1,1,1-trichloro-3-nitrobut-2- ene, under the same conditions, took an entirely different course and gave spiro-gem-dichlorocyclopropanes bearing a 1-nitroethyl moiety, with high diastereoselectivity and in good yields. © 2013 Elsevier Ltd. All rights reserved

An improved synthesis and some reactions of diethyl 4-oxo-4H-pyran-2,5- dicarboxylate

The reaction of ethyl 2-(dimethylamino)methylene-3-oxobutanoate with diethyl oxalate in the presence of sodium hydride in THF gave diethyl 4-oxo-4H-pyran-2,5-dicarboxylate, from which 4-oxo-4H-pyran-2,5-dicarboxylic and 4-oxo-1-phenyl-1,4-dihydropyridine-2,5-dicarboxylic acids and their derivatives were obtained in good yields. © 2013 Elsevier Ltd. All rights reserved

Domino reaction of 3-nitro-2-(trifluoromethyl)-2H-chromenes with 2-(1-phenylalkylidene)malononitriles: Synthesis of functionalized 6-(trifluoromethyl)-6H-dibenzo[b,d]pyrans and a rare case of [1,5] sigmatropic shift of the nitro group

A variety of functionalized 6-(trifluoromethyl)-6H-dibenzo[b,d]pyrans were easily synthesized in good yields under mild conditions by a domino reaction of 3-nitro-2-(trifluoromethyl)-2H-chromenes with 2-(1-phenylethylidene)- and 2-(1-phenylpropylidene)malononitriles. In the latter case, intermediate 7-amino-10-methyl-10-nitro-9-phenyl-6-(trifluoromethyl)-10,10a-dihydro-6H- benzo[c]chromene-8-carbonitriles were isolated as a result of a rare [1,5] sigmatropic shift of the nitro group. © 2013 Elsevier Ltd. All rights reserved

Synthesis of 5-(trifluoromethyl)-5H-chromeno[3,4-b]pyridines from 3-nitro-2-(trifluoromethyl)-2H-chromenes and aminoenones derived from acetylacetone and cyclic amines

Reactions of 3-nitro-2H-chromenes with aminoenones derived from acetylacetone and cyclic amines proceed diastereoselectively to give functionalized 2,3,4-trisubstituted chromanes as a result of nucleophilic addition of the vinylogous β-methyl group at the C-4 atom of the chromene system. From these compounds, under acidic conditions, 5-(trifluoromethyl)-5H- chromeno[3,4-b]pyridines and 4-acetoacetonyl-3-nitro-2-(trichloromethyl/phenyl) chromanes, depending on the substituent at the 2-position, were obtained in moderate to good yields. © 2013 Elsevier Ltd. All rights reserved