Mechanism of the photoreduction of N-Alkylbenzylidenimines

Padwa, Albert; Bergmark, William R.; Pashayan, Deran

doi:10.1021/ja01038a043

Cited by 80 publications

(21 citation statements)

References 4 publications

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“…Such a procedure produced a colourless material, and the absence of water was shown by Karl Fischer titration. A synthetic pathway to the molecules D, E, G, and H was successfully found following Padka et al (4) A mixture with equal amounts of aldehyde and amine and a catalytic amount of toluenesulfonic acid in toluene was refluxed and stirred for 24 h. Then the ctalyst was removed by washing with NaOH. The organic layer was dried over MgSO 4 , and the solvent was evaporated.…”

Section: Methodsmentioning

confidence: 99%

Thermochemistry of imines: experimental standard molar enthalpies of formation

Verevkin

Morgenthaler

Rüchardt

1997

The Journal of Chemical Thermodynamics

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Section: Methodsmentioning

confidence: 99%

Thermochemistry of imines: experimental standard molar enthalpies of formation

Verevkin

Morgenthaler

Rüchardt

1997

The Journal of Chemical Thermodynamics

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“…It is known in literature, that imines, in particular aldimines, can be photoreduced without any asymmetric induction in the presence of dihydropyridine Hantzsch esters 3 in benzene or of a ketone as photosensitizer in a protic solvent under illumination with a medium pressure mercury lamp. 34−37 In our case, employing toluene as solvent no product or byproduct formation could be detected when imine 2a and Hantzsch ester 3 were irradiated with the 365 nm LED for 24 h. The reduction under illumination was observed only in the presence of catalyst 1a .…”

Section: Resultsmentioning

confidence: 54%

Decrypting Transition States by Light: Photoisomerization as a Mechanistic Tool in Brønsted Acid Catalysis

2017

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Despite the wide applicability of enantioselective Brønsted acid catalysis, experimental insight into transition states is very rare, and most of the mechanistic knowledge is gained by theoretical calculations. Here, we present an alternative approach (decrypting transition state by light = DTS-hν), which enables the decryption of the transition states involved in chiral phosphoric acids catalyzed addition of nucleophiles to imines. Photoisomerization of double bonds is employed as a mechanistic tool. For this class of reactions four pathways (Type I Z, Type I E, Type II Z, Type II E) are possible, leading to different enantiomers depending on the imine configuration (E- or Z-imine) and on the nucleophilic attack site (top or bottom). We demonstrated that the imine double bond can be isomerized by light (365 nm LED) during the reaction leading to a characteristic fingerprint pattern of changes in reaction rate and enantioselectivity. This characteristic fingerprint pattern is directly correlated to the transition states involved in the transformation. Type I Z and Type II Z are demonstrated to be the competing pathways for the asymmetric transfer hydrogenation of ketimines, while in the nucleophilic addition of acetylacetone to N-Boc protected aldimines Type I E and Type II E are active. Accelerations on reaction rate up to 177% were observed for ketimines reduction. Our experimental findings are supported by quantum chemical calculations and noncovalent interaction analysis.

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“…Compounds Ia, Ib, Id, Ie [22], Ic [23], XIIIaXIIId [24], and XVII [25] were synthesized according to published procedures.…”

Section: Methodsmentioning

confidence: 99%

1,3-Dipolar Cycloaddition of Difluoro-Substituted Azomethine Ylides. Synthesis and Transformations of 2-Fluoro-4,5-dihydropyrroles

et al. 2005

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2-Fluoro-4,5-dihydropyrrole-3,4-dicarboxylic acid derivatives were obtained by reaction of difluorocarbene with N-substituted ketone imines in the presence of fumaronitrile, maleonitrile, or dimethyl maleate. The reaction involves intermediate formation of azomethine ylides and their subsequent cycloaddition at the double bond. 11H-Dibenz[b,e]azepine and 3,4-dihydroisoquinolines react with difluorocarbene in the presence of fumaronitrile to give fluoro-substituted dibenzo[c,f]pyrrolo[1,2-a]azepine and pyrrolo[2,1-a]-isoquinoline derivatives. Treatment of 2-fluoro-4,5-dihydropyrrole-3,4-dicarbonitrile with amines and alkoxides affords the corresponding 2-amino-and 2-alkoxy derivatives, while its reactions with hydrazine hydrate and benzimidamide lead to formation of substituted pyrrolo[2,3-c]pyrazole and pyrrolo[2,3-d]-pyrimidine derivatives.Pyrrole derivatives are widely used in synthetic and medical practice [1]. In the recent years, much attention was given to fluorinated pyrroles as potential biologically active substances. Several synthetic approaches to fluoropyrroles have been reported. Among these, direct fluorination of pyrrole derivatives [2, 3], transfunctionalization according to Schiemann [4], heterocyclization of fluorinated linear precursors [5], and 1,3-dipolar cycloaddition with participation of either fluorine-containing azomethine ylides [6][7][8] or fluorinated dipolarophiles [9, 10] must be noted.2-Fluoro-4,5-dihydropyrroles attract interest not only as potential biologically active substances but also as useful building blocks having a labile fluorine atom in the -position with respect to nitrogen. However, there are no convenient methods for the preparation of such compounds. Only two kinds of transformations are known to produce 2-fluoro-4,5-dihydropyrrole systems [11,12]. Photolytic ring contraction in N-substituted perfluoroazepines to give perfluoro-(3a,5a-dihydrocyclobuta[b]pyrroles) cannot be regarded as an acceptable synthetic route to 2-fluoro-4,5-dihydropyrroles, for its scope is limited to perfluorinated derivatives [11]. The reaction of N-methylpyrrolidone with carbonyl fluoride in the presence of cesium fluoride resulted in formation of only 4% of 2-fluoro-1-methyl-2,3-dihydropyrrole-3-carbonyl fluoride [12].We recently found that reactions of difluorocarbene with Schiff bases in the presence of 2-butenedioic acid derivatives could lead to 2-fluoro-4,5-dihydropyrroles in good yields [13]. The present article reports the results of our detailed study on the reactions of various ketone imines with difluorocarbene in the presence of fumaric and maleic acid derivatives as a method of synthesis of substituted 2-fluoro-4,5-dihydropyrroles and building up of a 2-fluoro-4,5-dihydropyrrole fragment as a part of a polycyclic system. Difluorocarbene was generated in situ by reduction of dibromodifluoromethane with lead in the presence of tetrabutylammonium bromide.The reactions of Schiff bases Ia-Id with difluorocarbene in the presence of fumaronitrile, maleonitrile, or dimethyl fumarate af...

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Mechanism of the photoreduction of N-Alkylbenzylidenimines

Cited by 80 publications

References 4 publications

Thermochemistry of imines: experimental standard molar enthalpies of formation

Thermochemistry of imines: experimental standard molar enthalpies of formation

Decrypting Transition States by Light: Photoisomerization as a Mechanistic Tool in Brønsted Acid Catalysis

1,3-Dipolar Cycloaddition of Difluoro-Substituted Azomethine Ylides. Synthesis and Transformations of 2-Fluoro-4,5-dihydropyrroles

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