- Using non-covalent interactions to direct regioselective 2+2 photocycloaddition within a macrocyclic cavitand
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The relative orientation of guests within ternary inclusion complexes is governed by the host-guest and guest-guest supramolecular interactions. Selectivity in 2+2 photocycloaddition between two alkenes included within a macrocyclic cavitand (γ-cyclodextrin) can be controlled using non-covalent interactions. In this manuscript, we report cavitand-mediated control of regioselectivity between alkyl cinnamates using non-covalent interactions. Using this method, we have shown that regioselectivity can be switched completely from a head-to-head dimer to a head-to-tail dimer. The reactions were also stereoselective in most cases. Stoichiometry experiments were performed to explore relative stabilities of the complexes, which indicate that the ternary complex is more stable than others. Selectivity in the photocycloaddition reaction was also applied retrospectively to deduce intermolecular orientations. Time-dependent conversion study we performed indicates that the observed reactivity of alkenes is representative of the intermolecular orientations in the bulk of the complex medium. Experimental observations and computational studies were used to qualitatively understand the complex structures, and relative magnitudes of the weak interactions. The reactions of complexes were studied in slurry form, and the extent of reaction control suggests a solid-state-like behavior.
- Nguyen, Nga,Clements, Aspen Rae,Pattabiraman, Mahesh
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p. 2433 - 2443
(2016/03/19)
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- Phospholane-catalyzed wittig reaction
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We identified 2-phenylisophosphindoline 2-oxide as a suitable and potentially tunable catalyst for the catalytic Wittig reaction of aldehydes with activated organohalides. This catalyst was obtained by a straightforward two-step synthesis. Trimethoxysilane proved to be an efficient reducing agent for the in situ generation and regeneration of the catalyst from the corresponding phosphane oxide. Sodium carbonate was identified as a suitable base for the transformation. It is noteworthy that the particle size of the sodium carbonate had a tremendous effect on the outcome of the reaction. Under the optimized reaction conditions, 23 aldehydes were converted into the corresponding alkenes in high isolated yields of up to 88%. Moreover, an asymmetric catalytic Wittig reaction was performed for the desymmetrization of a prochiral diketone.
- Werner, Thomas,Hoffmann, Marcel,Deshmukh, Sunetra
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p. 3286 - 3295
(2015/05/20)
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- Scope and Limitation of the Microwave-Assisted Catalytic Wittig Reaction
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We have developed a microwave-assisted catalytic Wittig reaction. In this paper, we give full account of the scope and limitations of this reaction. A screening of various commercially available phosphine oxides as precatalysts revealed Bu3P=O to be the most promising candidate. We tested 10 silanes for the in situ reduction of the phosphine oxide to generate Bu3P as the actual catalyst. Different epoxides were tested as masked bases. In this context, cyclohexene oxide as well as butylene oxide proved to be suitable. The reaction could be carried out at 125 C, but higher yields and E/Z selectivities were obtained at 150 °C. Under the optimised reaction conditions, more than 40 examples for the conversion of various aldehydes into the corresponding alkenes are reported. The products were obtained in yields of up to 88 with high E selectivities. Moreover, we also describe the further screening of several chiral phosphines as catalysts for the microwave-assisted enantioselective catalytic Wittig reaction. The scope and limitations of the microwave-assisted catalytic Wittig reaction have been evaluated with respect to the catalyst, silane, solvent, reaction conditions, and substrates.
- Hoffmann, Marcel,Deshmukh, Sunetra,Werner, Thomas
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p. 4532 - 4543
(2015/07/27)
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- First Microwave-Assisted Catalytic Wittig Reaction
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We introduce a novel catalytic Wittig reaction based on an inexpensive and readily available phosphane oxide as a precatalyst. The performance of the reaction under microwave irradiation led to significantly improved yields and reaction rates relative to those obtained under conventional heating. Moreover, herein we enclose the first example of the asymmetric catalytic Wittig reaction based on a chiral phosphane as the catalyst.
- Werner, Thomas,Hoffmann, Marcel,Deshmukh, Sunetra
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supporting information
p. 6873 - 6876
(2016/02/19)
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- Mild synthesis of mesoporous silica supported ruthenium nanoparticles as heterogeneous catalysts in oxidative Wittig coupling reactions
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A new efficient approach for the in situ synthesis of anchored ruthenium nanoparticles (RuNP) in three different kinds of mesoporous silica materials, MCM-41, SBA-15 and HMS, has been developed. Solids have been synthesized under very mild conditions from RuCl3·H2O salt reduced in one hour at room temperature in the mesoporous silicas previously grafted with aminopropyltriethoxysilane (APTES). Well-dispersed ruthenium nanoparticles, with an average size of 3 nm, anchored into the silica network by the APTES were obtained. These materials, with a molar ratio of Si/Ru = 40, were found to be catalytically active and selective in the alcohol oxidation-Wittig olefination. Interestingly, while the reaction occurs from the alcohol, control experiments suggest that the aldehyde (the common Wittig substrate) is not involved. The Royal Society of Chemistry.
- Carrillo, Adela I.,Schmidt, Luciana C.,Marin, M. Luisa,Scaiano, Juan C.
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supporting information
p. 435 - 440
(2014/02/14)
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- P[N(i-Bu)CH2CH2]3N: Nonionic Lewis base for promoting the room-temperature synthesis of α,β-unsaturated esters, fluorides, ketones, and nitriles using Wadsworth - Emmons phosphonates
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The bicyclic triaminophosphine P(RNCH2CH2) 3N (R = i-Bu, 1c) serves as an effective promoter for the room-temperature stereoselective synthesis of α,β-unsaturated esters, fluorides, and nitriles from a wide array of aromatic, aliphatic, heterocyclic, and cyclic aldehydes and ketones, using a range of Wadsworth-Emmons (WE) phosphonates. Among the analogues of 1c [R = Me (1a), i-Pr (1b), Bn (1d)], 1a and 1b performed well, although longer reaction times were involved, and 1d led to poorer yields than 1c. Functionalities such as cyano, chloro, bromo, methoxy, amino, ester, and nitro were well tolerated. We were able to isolate and characterize (by X-ray means; see above) the reactive WE intermediate species formed from 2b and 1c.
- Chintareddy, Venkat Reddy,Ellern, Arkady,Verkade, John G.
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supporting information; experimental part
p. 7166 - 7174
(2010/12/25)
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- Templating photodimerization of trans-cinnamic acid esters with a water-soluble Pd nanocage
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A water-soluble octahedral Pd nanocage acting as a reaction vessel templates the photodimerization of substituted trans-cinnamic acid methyl esters in water. Irradiation of the host-guest complexes of trans-cinnamic acid methyl esters with the Pd nanocage resulted in selective formation of a syn head-head dimer in addition to the corresponding cis isomer. These results suggest that the guest molecules are preoriented in a selective fashion with the hydrophilic ester group facing water and the hydrophobic aryl group tucked within the cavity of the host. Such an orientation occurs at the hydrophobic-hydrophilic interface between the nanocage exterior and interior. Weak intermolecular C-H-π and π-π interactions between the host and the guest(s) are likely to be responsible for the lack of mobility of the reactant olefins during their short excited-state lifetime.
- Karthikeyan,Ramamurthy
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p. 452 - 458
(2007/10/03)
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- Derivatives of 2-arylcyclopropylamine: Synthesis and interactions with 5-HT1A receptors
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A series of cis- and trans-derivatives of 2-aryl-N,N-dipropylcyclopropylamines and 1-(2-arylcyclopropyl)-N,N-dipropylmethylamines were synthesized and evaluated for affinity at the 5-HT1A receptor. The key step in the syntheses was a cyclopropanation of cis- and trans-3-arylpropenoic esters with diazomethane which proceeds with retention of the stereochemistry. cis-1-[2-(3-Methoxyphenyl)cyclopropyl]-N,N-dipropylmethylamine (32) had the highest 5-HT1A-receptor affinity (Ki= 58 nM) of the novel derivatives.
- Appelberg, Ulf,Mohell, Nina,Hacksell, Uli
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p. 415 - 420
(2007/10/03)
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