A Deep Cavitand Templates Lactam Formation in Water

Mosca, Simone; Yu, Yang; Gavette, Jesse V.; Zhang, Kang‐Da; Rebek, Julius

doi:10.1021/jacs.5b10028

Cited by 89 publications

(60 citation statements)

References 39 publications

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“…These three features strongly inter‐relate the origin of the catalytic effect. The effect would be complemented by stabilization of reactive intermediates and chemical processes, which are consequences inherent to such a limited space . The large reactive sites in 3 and 4 allow various transition‐state geometries, whereas the confined space in 2 limits the transition states and the desired reactive species may be actively stabilized .…”

Section: Resultsmentioning

confidence: 99%

Evaluation of the Reactivity of Metallocatalytic Cavities in the Dimerization of Terminal Alkynes

et al. 2016

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The effect of a metallocatalytic cavity flanked by aromatic rings on the catalytic dimerization of terminal alkynes was explored through a comparison with model catalysts that weakened the cavity. The diquinoxaline‐spanned resorcin[4]arene provided a definite compartment, in which the two Au centers enticed two alkynes to undergo the coupling reaction. We synthesized two kinds of model compounds in which one lacked two quinoxaline walls and the other had two pyrazine walls and found that these catalysts exhibited much lower reactivity. The two quinoxaline moieties proved to be quintessential for the catalytic event.

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Section: Resultsmentioning

confidence: 99%

Evaluation of the Reactivity of Metallocatalytic Cavities in the Dimerization of Terminal Alkynes

et al. 2016

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“…The cavitand's action is that of a template: Complexation "pushes" the termini closer together in the cavitand, and sites that are remote in bulk solvent are closer together in the complex (15,16). Reactions with macrocyclic transition structures are particularly enhanced, as shown recently for macrolactamization reactions (17).…”

Section: Resultsmentioning

confidence: 93%

“…The use of these cavitands offers the further advantage of providing a vehicle for moving organic reactions into water, providing accelerated rates for water-insoluble substrates. Additional applications of the cavitand in monofunctionalizations (26) and cyclizations to macrolactams (17) and ureas (27) augur well for remote functionalization reactions.…”

Section: Discussionmentioning

confidence: 99%

Water-soluble cavitands promote hydrolyses of long-chain diesters

Shi

Mower

Blackmond

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Water-soluble, deep cavitands serve as chaperones of long-chain diesters for their selective hydrolysis in aqueous solution. The cavitands bind the diesters in rapidly exchanging, folded J-shape conformations that bury the hydrocarbon chain and expose each ester group in turn to the aqueous medium. The acid hydrolyses in the presence of the cavitand result in enhanced yields of monoacid monoester products. Product distributions indicate a two-to fourfold relative decrease in the hydrolysis rate constant of the second ester caused by the confined space in the cavitand. The rate constant for the first acid hydrolysis step is enhanced approximately 10-fold in the presence of the cavitand, compared with control reactions of the molecules in bulk solution. Hydrolysis under basic conditions (saponification) with the cavitand gave >90% yields of the corresponding monoesters. Under basic conditions the cavitand complex of the monoanion precipitates from solution and prevents further reaction.M onofunctionalization of symmetrical compounds poses a general problem: When identical functional groups on a substrate are truly remote, they act independently, and reactions result in a statistical mixture of products. For example, hydrolysis of diesters ( Fig. 1) separated by a long methylene chain exhibits equal rate constants at each site (k 1 = k 2 ), which sets an upper limit of 36.8% for the yield of the monoester. This maximum occurs when comparable amounts of unreacted diester and doubly reacted diacid product are present ( Fig. 1), a factor that often complicates isolation of the desired monoester product.Special circumstances can favor monofunctionalization. When the monofunctionalized compound has fortuitously different properties (such as solubility) and can be removed to a different phase (1) as it is formed, good yields can result. Likewise, when the sites are not remote--as in diesters of oxalic acid--reaction at one site greatly modifies reactivity at the other site and affects the yield of the monofunctionalized product. We describe here the application of synthetic container compounds (cavitands) as molecular chaperones to address the monofunctionalization problem. Whereas the present examples involve only hydrolysis of long-chain diesters, the predictable influence of the cavitand promises wider applications in other reactions of symmetrical, difunctional substrates. Results and DiscussionWe recently reported the synthesis of deep cavitand 1 (Fig. 2) and its capacity to sequester hydrophobic and amphiphilic species in water (2). The eight methyl groups of cavitand 1 broaden its upper rim and prevent dimerization through hydrogen bonding into a capsule. The cavitand is stable over a wide pH range. Whereas a number of water-soluble, deep cavitand hosts are available (3-10), cavitand 1 bound long-chain guest alkanes and related difunctional compounds (bola-amphiphiles) in folded conformations (11). Folded alkyls inside a γ-cyclodextrin were initially characterized by Turro et al. (12), and folded bola-amphiphiles ...

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“…The ratio 7f / 7g decreased to 46:54 when cis ‐ 3· AuCl was used. These results indicate that less anisotropic effect in the cis ‐cavitand would cause less stabilization effect by π‐orbital mixing with reaction process, and that the geometrically open space in cis ‐form allows various transition‐state geometries to lower selectivity …”

Section: Resultsmentioning

confidence: 99%

Evaluation of the Catalytic Capability of cis‐ and trans‐Diquinoxaline Spanned Cavitands

et al. 2019

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Three new cis‐diquinoxaline spanned cavitands were successfully synthesized. These cis‐diphosphinated derivatives were applied in homogeneous gold‐catalyzed dimerization and hydration of alkynes as well as rhodium‐catalyzed styrene hydroformylation. The results were ranked with those obtained with their trans‐diphosphinated isomeric analogues. The structure‐activity relationship employing these two cavitands reveals that the cis‐ or trans‐positioning of the catalyst centers directly influences cooperation between the two metallic atoms to control catalytic activity, reaction profile, and product selectivity. This comparative study provides us an intellectual basis for future catalytic cavitand chemistry and homogeneous catalysis.

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A Deep Cavitand Templates Lactam Formation in Water

Cited by 89 publications

References 39 publications

Evaluation of the Reactivity of Metallocatalytic Cavities in the Dimerization of Terminal Alkynes

Evaluation of the Reactivity of Metallocatalytic Cavities in the Dimerization of Terminal Alkynes

Water-soluble cavitands promote hydrolyses of long-chain diesters

Evaluation of the Catalytic Capability of cis‐ and trans‐Diquinoxaline Spanned Cavitands

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