Halogen Bonding in Organic Synthesis and Organocatalysis

Bulfield, David; Huber, Stefan M.

doi:10.1002/chem.201601844

Cited by 525 publications

(374 citation statements)

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“…In contrast to more sophisticated systems,2, 11, 12 catalysts based on elements of row 4 and above failed to yield significant activity within this series of conceptually simple, neutral, and monodentate catalysts. This direct comparison ignores that pnictogen variants contain three activating substituents, whereas chalcogen ones contain only two and halogen variants only one.…”

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confidence: 63%

“…Integrating conceptually new non‐covalent interactions into functional systems is of fundamental importance 1, 2, 3, 4. It enables the creation of novel, unprecedented architectures and holds promise to access new properties.…”

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confidence: 99%

“…Arguably the best studied σ‐hole interaction is the halogen bond,9 which has found elegant applications in organocatalysis (Figure 2 a, green) 2. Possibly owing to higher steric demands, non‐covalent chalcogen bonding in solution has only recently received increased attention,10 and was applied to non‐covalent catalysis only last year (Figure 2 a, red) 11, 12.…”

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Catalysis with Pnictogen, Chalcogen, and Halogen Bonds

et al. 2018

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Halogen‐ and chalcogen‐based σ‐hole interactions have recently received increased interest in non‐covalent organocatalysis. However, the closely related pnictogen bonds have been neglected. In this study, we introduce conceptually simple, neutral, and monodentate pnictogen‐bonding catalysts. Solution and in silico binding studies, together with high catalytic activity in chloride abstraction reactions, yield compelling evidence for operational pnictogen bonds. The depth of the σ holes is easily varied with different substituents. Comparison with homologous halogen‐ and chalcogen‐bonding catalysts shows an increase in activity from main group VII to V and from row 3 to 5 in the periodic table. Pnictogen bonds from antimony thus emerged as by far the best among the elements covered, a finding that provides most intriguing perspectives for future applications in catalysis and beyond.

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Catalysis with Pnictogen, Chalcogen, and Halogen Bonds

et al. 2018

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“…Herein, we report the first direct α-N-glycosylation of amide with glycosyl trichloroacetimidate 12) using halogen bond (XB) donor 13) /Schreiner thiourea 14) co-catalytic system. We envisioned that α-selectivity would be achieved through the double inversion strategy (Chart 1b).…”

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confidence: 99%

“…According to our previous work, 2-iodoimidazolium salt (XB1) 13) was examined in conjunction with HB1 in dichloromethane. 8) As we expected, the combination of HB1 and XB1 was essential for the production of desired N-glycoside 2a (entries 1-3), although almost no α/β selectivity was observed (entry 3).…”

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Organocatalytic Direct α-Selective <i>N</i>-Glycosylation of Amide with Glycosyl Trichloroacetimidate

Kobayashi

Takemoto

2018

Chem. Pharm. Bull.

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Through the synergistic catalytic effect of the halogen bond (XB) donor and thiourea catalyst, a direct α-selective N-glycosylation of the amide residue of asparagine derivative was achieved using readily accessible glycosyl trichloroacetimidate. n-Butyl methyl ether was found to be the most suitable solvent for the α-selectivity.Key words glycosylation; organocatalyst; halogen bond; hydrogen bond; green chemistry N-Glycosides are found in a variety of bioactive compounds, including natural products. 1) Sugar moieties are known to extend the diversity of molecules, altering their property, structure, and biological activities. 2) However, synthetic methods for N-glycosides have not been well developed, [3][4][5][6][7][8] as compared with the preparation of O-glycosides. In particular, stereoselective synthesis of α-N-glycosides is one of the most challenging issues despite their potentials as therapeutic compounds. [9][10][11] In 2003, DeShong's group has reported a highly α-selective synthesis of N-glycosides through a Cu-mediated acylation of glycopyranosyl isoxazoline intermediates generated from the corresponding azides, 5) while anomerization of 1-aminoglycopyranosyl derivatives is generally a significant problem. 4) Direct N-glycosylation of amides has emerged as an alternative approaches, 6-8) but those reports relied on the neighboring group participation to give β-N-glycosides (Chart 1a).Herein, we report the first direct α-N-glycosylation of amide with glycosyl trichloroacetimidate 12) using halogen bond (XB) donor 13) /Schreiner thiourea 14) co-catalytic system. We envisioned that α-selectivity would be achieved through the double inversion strategy (Chart 1b). The initial S N 2 addition of an appropriate solvent, such as etheric solvent, and/or additive 15) to α-donor 1 would form a β-linked intermediate A, to which the following S N 2 attacked by an employed amide would afford the desired α-linked product. As in our previous report, 8) we have chosen an XB-donor/thiourea co-catalytic system for the activation of the leaving group (LG) of 1, mainly due to the following reasons: 1) XB interaction would be effective in relatively polar etheric solvent, and 2) tuning of both HB donor and XB donor would improve their ability to trap the LG via anion binding, 16) preventing the undesired rearrangement of the LG.We first screened the reaction conditions for the direct α-N-glycosylation of asparagine derivative 3 with glycosyl donor 1 (Table 1). According to our previous work, 2-iodoimidazolium salt (XB1) 13) was examined in conjunction with HB1 in dichloromethane. 8) As we expected, the combination of HB1 and XB1 was essential for the production of desired N-glycoside 2a (entries 1-3), although almost no α/β selectivity was observed (entry 3). A control experiment with non-halogenated azolium 5 did not furnish 2a at all (entry 4), indicating that XB interaction would play an important role. The chemical yields were slightly improved using XB2 and XB3 (entries 5 and 6), whereas the undesired glycosyl trichl...

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Structural Chemistry of Hypervalent Iodine Compounds

Justik

2018

Patai's Chemistry of Functional Groups

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To quote the modernist architectural mantra: “form follows function.” HVI compounds possess highly unique geometric features, which are highly tunable toward reactivity, making them impressively useful tools in modern synthetic chemistry. This chapter will endeavor to discuss the latest investigations into the structures of λ 3 ‐ and λ 5 ‐iodanes and revisit the past work with fresh insight. A new taxonomy for organizing hypervalent iodine compounds by structure will be introduced. The latest understanding of halogen bonding will be applied to the long‐observed “secondary‐bonding” interactions present in many solid‐state structures. These interactions are now understood to play a key role in the opening stages of reaction mechanisms involving hypervalent iodine reagents, especially in arylation chemistry. The X‐ray crystallographic data from a representative scope of iodanes will be complied in one work, as an easily accessible reference for those new to the field or those cogitating new possible structural motifs to solve synthetic challenges.

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Halogen Bonding in Organic Synthesis and Organocatalysis

Cited by 525 publications

References 142 publications

Catalysis with Pnictogen, Chalcogen, and Halogen Bonds

Catalysis with Pnictogen, Chalcogen, and Halogen Bonds

Organocatalytic Direct α-Selective <i>N</i>-Glycosylation of Amide with Glycosyl Trichloroacetimidate

Structural Chemistry of Hypervalent Iodine Compounds

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