Concerning the Problem of Stereospecific Glycosylation. Synthesis and Methanolysis of some 2-<i>O</i>-Benzylated <scp>D</scp>-Galactopyranosyl and <scp>D</scp>-Galactofuranosyl Halides

Fréchet, Jean M. J.; Baer, Hans H.

doi:10.1139/v75-094

Cited by 19 publications

(5 citation statements)

References 13 publications

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“…The C-4 and C-6 hydroxy groups of starting materials were protected as benzylidene acetal 21 and the C-2 and C-3 hydroxy groups were O-benzylated. 22,23 Removal of the benzylidene groups 24,25 followed by regioselective replacement of the hydroxy groups at C-6 by iodine atom 7,26 and substitution of iodine atom by azido group 6,7,27 furnished 13a 7 and 13b, 6 known 6-azido-4-hydroxy derivatives. O-allylation of C-4 hydroxy groups of 13a and 13b 6,7,23 gave 14a 7 and 14b, 6 also known compounds.…”

Section: Resultsmentioning

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

J. Braz. Chem. Soc.

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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...

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Section: Resultsmentioning

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

J. Braz. Chem. Soc.

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“…18 Removal of the benzylidene group 19 following by regioselective replacement of the hydroxyl group at C-6 by iodine atom, 2,20 substitution 365 Oliveira et al Vol. 18, No.…”

Section: Resultsmentioning

confidence: 99%

tri-n-butyltin hydride-mediated radical reaction of a 2-iodobenzamide: formation of an unexpected carbon-tin bond

Oliveira¹,

Prado²,

Alves³

et al. 2007

J. Braz. Chem. Soc.

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metila. A estrutura do produto foi elucidada por meio das espectrometrias de RMN unidimensionais ( 1 H, 13 C e DEPT) e bidimensionais (COSY e HMQC) e confirmada por espectrometria de massas. Foram apresentadas propostas de mecanismos para explicar a formação do derivado organoestanho.The tri-n-butyltin hydride-mediated reaction of methyl 2,3-di-O-benzyl-4-O-trans-cinnamyl-6-deoxy-6-(2-iodobenzoylamino)-α-D-galactopyranoside afforded an unexpected aryltributyltin compound. The structure of this new tetraorganotin(IV) product has been elucidated by 1 H, 13 C NMR spectroscopy, COSY and HMQC experiments and electrospray ionization mass spectrometry (ESI-MS). The formation of this new compound via a radical coupling reaction and a radical addition-elimination process is discussed. Keywords: tetraorganotin, arylstannane, aryl radical cyclization, 2-iodobenzamide IntroductionIn our studies of Bu 3 SnH-mediated radical cyclizations, we have applied unsaturated organohalides to synthesize large-and medium-size heterocycles. [1][2][3][4][5][6][7][8] Most particularly, ortho-iodobenzamides bearing a side allyloxy group have been used to form benzomacrolactams with 11-, 12-and 20-membered ring via regioselective endo aryl radical cyclization. [1][2][3][4][5] In this context, the benzamide methyl 4-Oallyl-2,3-di-O-benzyl-6-deoxy-6-(2-iodobenzoylamino)-α-D-galactopyranoside (1) was found to give the benzomacrolactam 2 owing to 11-endo cyclization in 32% yield. 2To continue these studies, we applied the Bu 3 SnHmediated radical reaction in an attempt to form the benzomacrolactams 3 and/or 4 from methyl 2,3-di-O-benzyl-4-O-trans-cinnamyl-6-deoxy-6-(2-iodobenzoylamino)-α-Dgalactopyranoside (5), a cinnamylated analogue of 1. Despite our knowledge of preferential endo cyclization mode over the exo-mode in macrocyclization reactions, 1-5,9-16 we expected that 10-exo cyclization could also occur due to the higher stability of the benzyl radical. This hypothesis was supported by the observation that precursors with cinnamyl group provided macrocycle intermediates resulting from 10-exo carbocyclization.6 Moreover, the cinnamyl moiety of 5 would generate a new stereogenic center upon 10-exo or 11-endo cyclization, hence the stereoselectivity of the reaction could be evaluated. In fact, the tri-n-butyltin hydridemediated reaction of 5 afforded an unexpected aryltributyltin compound. Results and DiscussionTo prepare the iodobenzamide 5, the C-4 and C-6 hydroxyl groups of methyl α-D-galactopyranoside were protected as benzylidene acetal 17 and the C-2 and C-3 hydroxyl groups were O-benzylated. 18 Removal of the benzylidene group 19 following by regioselective replacement of the hydroxyl group at C-6 by iodine atom, 2,20 substitution 365 Oliveira et al. Vol. 18, No. 2, 2007 of iodine atom by azido group 2,21 and O-cinnamylation of C-4 hydroxyl group 22 gave the methyl 6-azido-2,3-di-O-benzyl-4-O-trans-cinnamyl-6-deoxy-α-D-galactopyranoside (6). Selective reduction of the azido group 23 gave the expected amine 7, which upon treatment w...

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“…A benzamida 23 foi submetida à reação de ciclização radicalar nas condições preconizadas para se minimizar a formação do produto de hidrogenólise e a ocorrência de reações intermoleculares (alta diluição e adição lenta da solução de Bu 3 SnH e quantidade catalítica de AIBN em benzeno sobre a solução de 23 em benzeno, sob refluxo [29][30][31] Considerando-se a falha na rota de síntese planejada, que inviabilizou a obtenção do derivado 29, foi proposto outro caminho para sua síntese (Figura 12), utilizando-se o 2,3-di-O-benzil-α-Dgalactopiranosídeo de metila (36) como material de partida (sintetizado a partir do α-D-galactopiranosídeo de metila 19,21,32,33 ). Protegeu-se a hidroxila de C-6 na forma de éter tert-butildimetilsilílico 23 e, em seguida, promoveu-se a mesilação da hidroxila de C-4 34 .…”

Section: Resultsunclassified

Síntese de aliloxi-orto-iodobenzamida derivada de d-glicose e reação de ciclização radicalar mediada por hidreto de tri-n-butilestanho

Dias¹,

Prado²,

Pinto³

et al. 2006

Quím. Nova

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Concerning the Problem of Stereospecific Glycosylation. Synthesis and Methanolysis of some 2-O-Benzylated D-Galactopyranosyl and D-Galactofuranosyl Halides

Cited by 19 publications

References 13 publications

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

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

tri-n-butyltin hydride-mediated radical reaction of a 2-iodobenzamide: formation of an unexpected carbon-tin bond

Síntese de aliloxi-orto-iodobenzamida derivada de d-glicose e reação de ciclização radicalar mediada por hidreto de tri-n-butilestanho

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