| 1. |
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| 2. |
- Alam, Rauful, et al.
(författare)
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Stereoselective allylboration of imines and indoles under mild conditions. An in situ E/Z isomerization of imines by allylboroxines
- 2014
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 5:7, s. 2732-2738
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Tidskriftsartikel (refereegranskat)abstract
- Direct allylboration of various acyclic and cyclic aldimine, ketimine and indole substrates was performed using allylboronic acids. The reaction proceeds with very high anti-stereoselectivity for both E and Z imines. The allylboroxines formed by dehydration of allylboronic acids have a dual effect: promoting E/Z isomerization of aldimines and triggering the allylation by efficient electron withdrawal from the imine substrate.
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| 3. |
- Barbion, Julien, et al.
(författare)
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Stereoselective functionalization of pyrrolidinone moiety towards the synthesis of salinosporamide A
- 2012
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 68:32, s. 6504-6512
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Tidskriftsartikel (refereegranskat)abstract
- An important feature of the synthesis of salinosporamide A. a potent proteasome inhibitor, is the establishment of the quaternary stereocenter at C3. A new route has been developed based on the methylation of a functionalized pyrrolidinone. Direct methylation reaction led to the unwanted diastereomer: however, by means of a Corey-Chaykovsky reaction followed by LiAlH4 epoxide opening, the desired alcohol was obtained. The pyrrolidinone was elaborated through a key allylation reaction between a tertiary allyltitanium reagent and an aldehyde bearing a spiroketal moiety in alpha-position.
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| 4. |
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| 5. |
- Biosca, Maria, et al.
(författare)
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Mechanism of Asymmetric Homologation of Alkenylboronic Acids with CF3-Diazomethane via Borotropic Rearrangement
- 2024
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Ingår i: Journal of Organic Chemistry. - 0022-3263 .- 1520-6904. ; 89:7, s. 4538-4548
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory calculations have been performed to investigate the mechanism for the BINOL-catalyzed asymmetric homologation of alkenylboronic acids with CF3-diazomethane. The reaction proceeds via a chiral BINOL ester of the alkenylboronic acid substrate. The calculations reveal a complex scenario for the formation of the chiral BINOL-alkenylboronate species, which is the key intermediate in the catalytic process. The aliphatic alcohol additive plays an important role in the reaction. This study provides a rationalization of the stereoinduction step of the reaction, and the enantioselectivity is mainly attributed to the steric repulsion between the CF3 group of the diazomethane reagent and the γ-substituent of the BINOL catalyst. The complex potential energy surface obtained by the calculations is analyzed by means of microkinetic simulations.
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| 6. |
- Biswas, Srijit, et al.
(författare)
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Atom-Efficient Gold(I)-Chloride-Catalyzed Synthesis of alpha-Sulfenylated Carbonyl Compounds from Propargylic Alcohols and Aryl Thiols : Substrate Scope and Experimental and Theoretical Mechanistic Investigation
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:52, s. 17939-17950
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Tidskriftsartikel (refereegranskat)abstract
- Gold(I)-chloride-catalyzed synthesis of -sulfenylated carbonyl compounds from propargylic alcohols and aryl thiols showed a wide substrate scope with respect to both propargylic alcohols and aryl thiols. Primary and secondary aromatic propargylic alcohols generated -sulfenylated aldehydes and ketones in 60-97% yield. Secondary aliphatic propargylic alcohols generated -sulfenylated ketones in yields of 47-71%. Different gold sources and ligand effects were studied, and it was shown that gold(I) chloride gave the highest product yields. Experimental and theoretical studies demonstrated that the reaction proceeds in two separate steps. A sulfenylated allylic alcohol, generated by initial regioselective attack of the aryl thiol on the triple bond of the propargylic alcohol, was isolated, evaluated, and found to be an intermediate in the reaction. Deuterium labeling experiments showed that the protons from the propargylic alcohol and aryl thiol were transferred to the 3-position, and that the hydride from the alcohol was transferred to the 2-position of the product. Density functional theory (DFT) calculations showed that the observed regioselectivity of the aryl thiol attack towards the 2-position of propargylic alcohol was determined by a low-energy, five-membered cyclic protodeauration transition state instead of the strained, four-membered cyclic transition state found for attack at the 3-position. Experimental data and DFT calculations supported that the second step of the reaction is initiated by protonation of the double bond of the sulfenylated allylic alcohol with a proton donor coordinated to gold(I) chloride. This in turn allows for a 1,2-hydride shift, generating the final product of the reaction.
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| 7. |
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| 8. |
- Brea, Oriana, et al.
(författare)
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Mechanism(s) of thermal decomposition of N-Nitrosoamides : A density functional theory study
- 2019
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 75:8, s. 929-935
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Tidskriftsartikel (refereegranskat)abstract
- The thermal decomposition of N-nitrosoamides has experimentally been demonstrated to depend on several factors, such as temperature, solvent and the substituents on the substrate. Consequently, a number of reaction mechanisms have been proposed for this process in the literature. In this work, we present a comprehensive computational investigation in which we examine the detailed reaction mechanisms for two N-nitrosoamides (with aliphatic and aromatic substituents) in two different solvents (mesitylene and methanol). It is shown that the reaction mechanism can change dramatically with the nature of the substrate and the choice of solvent. Importantly, it is found that the polar solvent stabilizes ion-pairs that are unstable in the non-polar solvent, which can play a key role in the mechanism.
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| 9. |
- Brea, Oriana, et al.
(författare)
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Mechanisms of Formation and Rearrangement of Benziodoxole-Based CF3 and SCF3 Transfer Reagents
- 2020
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:23, s. 15577-15585
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Tidskriftsartikel (refereegranskat)abstract
- Togni's benziodoxole-based reagents are widely used in trifluoromethylation reactions. It has been established that the kinetically stable hypervalent iodine form (I-CF3) of the reagents is thermodynamically less stable than its acyclic ether isomer (O-CF3). On the other hand, the trifluoromethylthio analogue exists in the thermodynamically stable thioperoxide form (O-SCF3), and the hypervalent form (I-SCF3) has been elusive. Despite the importance of these reagents, very little is known about the reaction mechanisms of their syntheses, which has hampered the development of new reagents of the same family. Herein, we use density functional theory calculations to understand the reasons for the divergent behaviors between the CF3 and SCF3 reagents. We demonstrate that they follow different mechanisms of formation and that the metals involved in the syntheses (potassium in the case of the trifluoromethyl reagent and silver in the trifluoromethylthio analogue) play key roles in the mechanisms and greatly influence the possibility of their rearrangements from the hypervalent (I-CF3, I-SCF3) to the corresponding ether-type form (O-CF3, O-SCF3).
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| 10. |
- Brea, Oriana, et al.
(författare)
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Modeling Decomposition of N-Nitrosoamides in a Self-Assembled Capsule
- 2019
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:11, s. 7354-7361
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory calculations are employed to investigate the mechanism and energies of the decomposition of N-nitrosoamides in the presence of a resorcinarene-based self-assembled nanocapsule. From experiments, it is known that confinement in the capsule inhibits the thermal decomposition of these compounds. N-Nitrosoamides with both aromatic and aliphatic substituents are considered here and the calculations show that, for both kinds, binding to the capsule leads to a significant increase in the energy barrier of the rate-determining step, the 1,3 N -> O acyl transfer reaction. A distortion-interaction analysis is conducted to probe the reasons behind the inhibition of the reaction. In addition, we characterized hypothetical intermediates that might be involved in the formation of the decomposition products inside the capsule. Interestingly, it is found that the capsule stabilizes ion-pair species that are unstable in mesitylene solution. Finally, a possible explanation is proposed for the observed encapsulation of the decomposition product of only one of the substrates.
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