Probing the Mechanism of the Baylis–Hillman Reaction by Electrospray Ionization Mass and Tandem Mass Spectrometry

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Descrevemos nesse trabalho um método simples e eficiente para a preparação diastereosseletiva de b-piperonil-g-butirolactonas hidroxiladas, a partir de um aduto de Morita-Baylis-Hillman. Para exemplificar a eficiência dessa abordagem descrevemos também as sínteses das lignanas biologicamente ativas, (±)-yateína, (±)-podorizol e (±)-epi-podorizol.Starting from a Morita-Baylis-Hillman adduct we describe a simple and very efficient method for the diastereoselective preparation of hydroxylated b-piperonyl-g-butyrolactones. To exemplify the efficiency of this approach we also describe a highly efficient synthesis for the biologically active lignans (±)-yatein, (±)-podorhizol and (±)-epi-podorhizol.

Section: Resultsmentioning

confidence: 99%

Diastereoselective synthesis of β-piperonyl-γ-butyrolactones from morita-baylis-hillman adducts. highly efficient synthesis of (±)-yatein, (±)-podorhizol and (±)-epi-podorhizol

Trazzi¹,

Andre²,

Coelho³

2010

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“…The reactions were performed in a sealed syringe as the reactional medium directly coupled to ion-source. 25 The proposed intermediates for the catalytic cycle of the reaction (Scheme 3) were successfully intercepted and structurally characterized for the first time using ESI-MS and MS/ MS. Strong evidence was collected corroborating the currently accepted mechanism. 26 In a similar manner, online monitoring of Baylis-Hillman reactions co-catalyzed by ionic liquids achieved the gas phase supramolecular species responsible for the co-catalytic role of ionic liquids in the reaction.…”

Section: The Baylis-hillman Reactionmentioning

confidence: 99%

What do we know about reaction mechanism? the electrospray ionization mass spectrometry approach

Santos¹

2011

O fascínio do homem por reações químicas remonta aos tempos antigos. Com a introdução de técnicas espectroscópicas, a arte de explorar as reações se tornou uma ciência intrigante. Portanto, não é surpreendente que uma das fronteiras mais prósperas e gratificantes na Química moderna é o estudo de mecanismo de reações em processos químicos e biológicos. Como a imaginação do homem não termina nas fronteiras definidas pela natureza, e com o poder crescente da catálise, o químico orgânico sintético está pronto para contribuir de uma maneira importante no invento e desenvolvimento de novas tecnologias que permitam a geração de novos catalisadores e metodologias. Neste account uma nova ferramenta para acelerar o desenvolvimento na descoberta de novas reações é revisada através do monitoramento por espectrometria de massa com ionização eletrospray (ESI-MS).Man's fascination with chemical reactions goes back to ancient times. With the introduction of spectroscopic techniques, the art of exploiting reactions became an intriguing science. It is, therefore, not surprising that one of the most flourishing and rewarding frontiers in modern Chemistry is the study of reaction mechanisms in chemical and biological processes. As man's imagination does not stop at the frontiers defined by nature, and with the ever increasing power of catalysis, the synthetic organic chemist is poised to make important contributions by inventing and developing new enabling technologies for the generation of new catalysts and methodologies. In this account is offered a new tool for accelerating the development through electrospray ionizationmass spectrometric (ESI-MS) monitoring in new reaction discovering.

“…ESI(+)-MS spectra were obtained using a Micromass QTof hybrid quadrupole time-of-flight mass spectrometer operating at 7.000 mass resolution and 5 ppm mass accuracy using typical analytical conditions as described elsewhere. 38 ESI-MS and ESI-MS/MS were acquired in a QTof Waters Micromass mass spectrometer using positive ion mode from 1:1 H 2 OMeOH solutions with addition of a few microlitres of formic acid, and using the following basic operation conditions: capillary and cone voltages were set to 3500 V and 45 V, respectively, with a de-solvation temperature of 100 o C. For the tandem MS experiments, 15 eV collisions with argon were used. The solutions were infused directly into the ESI source by means of syringe pump (Harvard Apparatus) at a flow rate of 10 μL min -1 .…”

Section: General Methodsmentioning

confidence: 99%

Tri-n-butyltin Hydride-Mediated radical reactions of ortho-and meta-Iodobenzamides to synthesize benzomacrolactams: surprising formation of biphenyl compounds from meta-regioisomers

Faraco¹,

Oliveira²,

Pinto³

et al. 2009

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em diferentes condições. Dependendo das condições, os três precursores que contêm o átomo de iodo em posição meta conduziram a uma surpreendente quantidade de compostos bifenílicos, nos quais o átomo de iodo foi substituído por um grupo fenila. O substrato 2-iodobenzamida levou apenas ao produto de hidrogenólise. Nenhum produto ciclizado foi isolado de nenhuma das reações. As estruturas dos compostos bifenílicos inéditos foram elucidadas utilizando-se as espectrometrias de massa, de RMN 1 H e 13 C e experimentos DEPT, COSY, HMQC e HMBC. Foram propostos mecanismos de formação dos compostos bifenílicos e hipóteses para explicar os diferentes comportamentos dos isômeros orto-e metaiodobenzamidas na reação radicalar.Reactions of methyl 4-O-allyl-2,3-di-O-benzyl-6-deoxy-6-(3-iodobenzoylamino)-α-Dgalactopyranoside, its gluco epimer, methyl 2,3-di-O-benzyl-6-deoxy-6-(3-iodobenzoylamino)-4-O-(1-pentenyl)-α-D-glucopyranoside and its ortho-regioisomer with tri-n-butyltin hydride were performed in different conditions. Depending on reaction conditions the three meta-iodo isomers gave a surprising amount of biphenyl compounds. The 2-iodo isomer led only to the undesired but expected hydrogenolysis product. No cyclized products were isolated in all the reactions. The structures of the new biphenyl products were elucidated by 1 H and 13 C NMR spectroscopy, DEPT, COSY, HMQC and HMBC experiments and ESI-MS/MS. Mechanisms for the formation of these new biphenyl derivatives and hypotheses to explain the different outcomes for radical reactions of 3-or 2-iodobenzamides were presented. Keywords: biphenyl compounds, aryl radical cyclization, 3-and 2-iodobenzamides IntroductionIn view of the numerous biological activities of macrolactams [1][2][3][4] and the synthetic challenge they present, 3,5 we have studied the Bu 3 SnH-mediated radical cyclization reactions using unsaturated iodides as precursors of macrolactams, 6-12 mainly allyloxy-ortho-iodobenzamides derived from carbohydrates to give benzomacrolactams. [6][7][8][9][10][11] These precursors furnished benzomacrolactams with 11-, 12-and 20-membered ring by regioselective endo aryl radical carbocyclization. [6][7][8][9] The benzamides methyl 4-Oallyl-2,3-di-O-benzyl-6-deoxy-6-(2-iodobenzoylamino)-α-D-galactopyranoside (1) and its gluco epimer 2 were found to furnish the benzomacrolactams 3 and 4 owing to 11-endo cyclization in 32% and 40% yield, respectively 6,7 ( Figure 1).Considering that (i) we have been stimulated to study the Bu 3 SnH-mediated radical reactions to construct Faraco et al. 1505 Vol. 20, No. 8, 2009 macrocycles, since there is a limited number of protocols available for the synthesis of large rings using free radical-mediated macrocyclizations, 13 (ii) the endomacrocyclization mode is favoured over the exo, [6][7][8][9]12,[14][15][16][17][18][19][20] (iii) the carbohydrate moiety impose conformational restriction to favour cyclization, [6][7][8][9]12 and (iv) although the majority of fused aromatic macrocycles have been obtained from ortho-halogenobenzene...