Theoretical investigation of the Diels-Alder reactions of unsaturated boronates

The Diels-Alder reactions of simple unsaturated boronates have been investigated using computational methods and the results were compared with those for the analogue dihalo- and dialkylboranes. Our results indicate that the activating effect of the boronate moiety is small. All the studied reactions are concerted normal electron-demand Diels-Alder reactions with asynchronous transition structures and weak [4 + 3] C-B secondary orbital interactions, which explains the low experimental reactivity. Both electronic and steric effects contribute to give the observed low stereo- and regioselectivities.Fil: Pellegrinet, Silvina Carla. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; ArgentinaFil: Grimblat, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; Argentin

Looking at the big picture in activation strain model/energy decomposition analysis: The case of the: Ortho - Para regioselectivity rule in Diels-Alder reactions

The regioselectivity of the Diels-Alder reaction is predicted by the ortho-para rule which has been explained from FMO theory. Using DFT calculations, the activation-strain model and energy decomposition analysis we studied the reaction of methyl acrylate with four unsymmetrical dienes. We found that if the analysis is carried out considering the TS structures, the selectivity would not be explained by the interaction energy as expected considering the FMO arguments. However, a thorough analysis along the reaction path revealed that the interaction energy is responsible for the regioselectivity. A deeper analysis with the EDA model showed that the decisive term that accounts for the HOMO-LUMO interactions favors the ortho and para paths, as predicted by FMO arguments.Fil: Grimblat, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Sarotti, Ariel Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentin

Reactivity and Selectivity of Boron-Substituted Alkenes in the Diels-Alder Reaction with Cyclopentadiene. A Study of the Electron Charge Density and Its Laplacian

The effect of the nature of the boron moiety upon the reactivity and the selectivity of a variety of vinylboron dienophiles (1−12) in the Diels−Alder (DA) reaction was investigated using density functional theory and the quantum theory of atoms in molecules. The calculated reactivity of the dienophiles decreases in the order vinylborane (1) > dihalovinylboranes (2−4) > dialkylvinylboranes (5−7) ≈ vinyl boronic acid (8) > vinylboronates (9, 10) > vinyl MIDA boronate (11) ≈ vinyltrifluoroborate (12). The DA reactions of 1−7 were slightly endo-selective due to the stronger C6−B secondary orbital interaction in the endo transition structures (TSs) evaluated by the C6|B delocalization index. In the TSs of 5 and 7, a combination of electronic and steric factors reduce the endo selectivity. The moderate exo selectivity calculated for the DA reactions of boronates 8−11 was attributed mainly to the hydrogen bond between the oxygen atom of boronate moieties and one of the acidic hydrogens of the methylene of cyclopentadiene in the exo TSs, which also reduces the ability of the oxygen lone pairs to donate electron density into the vacant boron orbital. Interestingly, the cooperative effect between the two hydrogen bonds in the exo TS of the DA reaction of vinyltrifluoroborate (12) determines the almost exclusive exo selectivity predicted for this DA reaction. We propose that the relative reactivities of the dienophiles can be estimated by the charge density (ρr) and its Laplacian (∇2 ρr) at the (3,+1) critical point in the topology of ∇2 ρr, evaluated at the reactant molecules in the ground state. The profiles of the several topological parameters along the reaction are affected by the nature of the substituents attached to the boron atom and by the mode of addition (endo and exo) in the DA reactions.Fil: Vallejos, Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; ArgentinaFil: Grimblat, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; ArgentinaFil: Pellegrinet, Silvina Carla. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; Argentin

Diels-Alder Reactions of Pinacol Alkenylboronates: An experimental and theoretical study

We have studied the Diels-Alder reactions of pinacol alkenylboronates with cyclopentadiene under two different sets of conditions: thermal heating at 170 C in a pressure tube and with catalytic TFA (5 mol%) at 80 °C. Yields varied significantly from system to system and also for the uncatalyzed and catalyzed methodologies. Moderate to excellent exo-stereoselectivities were obtained in all cases. The theoretical study of the thermal reactions sheds some light on the intriguing substituent effects observed experimentally. A variety of substituted 5-norbornen-2-ols were easily generated by subsequent in situ oxidation of the cycloadducts with alkaline hydrogen peroxide.Fil: Vallejos, Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Grimblat, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Pellegrinet, Silvina Carla. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentin

A Hydrogen Bond Rationale for the Enantioselective beta-Alkenylboration of Enones Catalyzed by O-Monoacyltartaric Acids

DFT calculations suggest that O-monoacyl L-tartaric acids catalyze the asymmetric conjugate alkenylboration of enones through transition structures that are stabilized by hydrogen-bonding interactions. Formation of a fivemembered acyloxyborane is proposed. The hydrogen of the free carboxy group derived from the catalyst interacts with the carbonyl group of the cyclic acyloxyborane, stabilizing the transition structure and reducing the flexibility of the system. Additional stabilizing nonclassical CH···O hydrogen-bond interactions seem to determine the observed enantioselectivity.Fil: Grimblat, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; ArgentinaFil: Sugiura, Masaharu. Kumamoto University. Graduate School of Pharmaceutical Sciences; JapónFil: Pellegrinet, Silvina Carla. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; Argentin

Beyond DP4: An Improved Probability for the Stereochemical Assignment of Isomeric Compounds using Quantum Chemical Calculations of NMR Shifts

The DP4 probability is one of the most sophisticated and popular approaches for the stereochemical assignment of organic molecules using GIAO NMR chemical shift calculations when only one set of experimental data is available. In order to improve the performance of the method, we have developed a modified probability (DP4+), whose main differences from the original DP4 are the inclusion of unscaled data and the use of higher levels of theory for the NMR calculation procedure. With these modifications, a significant improvement in the overall performance was achieved, providing accurate and confident results in establishing the stereochemistry of 48 challenging isomeric compounds.Fil: Grimblat, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Zanardi, Maria Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Sarotti, Ariel Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentin

Combining the power of J coupling and DP4 analysis on stereochemical assignments: the J -DP4 methods

A systematic study to include 3JHH couplings into DP4 formalism (J-DP4) led to the development of three alternative strategies. The dJ-DP4 (direct) approach involves a new DP4-like equation including an additional probability term given by 3JHH. The iJ-DP4 (indirect) approach explores the original DP4 method with a restricted conformational search. Despite both strategies performing better than DP4, their combined use (iJ/dJ-DP4) provided the best results, with a 2.5-fold performance improvement at similar or lower computational cost.Fil: Grimblat, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Gavín, José A.. Universidad de la Laguna. Departamento de Química Orgánica. Instituto Universitario de Bio-Orgánica "Antonio González"; EspañaFil: Hernández Daranas, Antonio. Consejo Superior de Investigaciones Científicas; EspañaFil: Sarotti, Ariel Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentin

α-Hydroxyacids accelerate the Diels-Alder reaction of dibutyl vinylboronate with cyclopentadiene: Experimental results and mechanistic insights

We have found that α-hydroxyacids accelerate the Diels-Alder reaction of dibutyl vinylboronate with cyclopentadiene. When stoichiometric quantities are used, excellent yields are obtained, while catalytic activities are moderate. DFT calculations suggested that the activation of the dienophile occurs by ligand exchange with both functionalities of the α-hydroxyacid.Fil: Grimblat, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Sarotti, Ariel Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Pisano, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Pellegrinet, Silvina Carla. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentin

Transient imine as a directing group for the Pd-catalyzed anomeric C(sp)3-H arylation of 3-aminosugars

The first example of Pd(II)-catalyzed anomeric arylation of 3-aminosugars is reported by using an L,X-type transient directing groups (TDG) approach combined with an external 2-pyridone ligand. The released free amine was in situ transformed into an azide function, which was then exploited in a CuAAC to increase the molecular complexity and prepare a variety of complex substituted C3-triazolo C-glycosides in good yields

Palladium(II)-Catalyzed Annulative Difunctionalization of Two Inert C(sp 3 )–H Bonds by a Bifunctional Reagent

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