Browse
Submit Data
Databases
API
Help

Dataset Information

11 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

The origin of the ligand-controlled regioselectivity in Rh-catalyzed [(2 + 2) + 2] carbocyclizations: steric vs. stereoelectronic effects.

ABSTRACT: Density functional theory calculations demonstrate that the reversal of regiochemical outcome of the addition for substituted methyl propiolates in the rhodium-catalyzed [(2 + 2) + 2] carbocyclization with PPh3 and (S)-xyl-binap as ligands is both electronically and sterically controlled. For example, the ester functionality polarizes the alkyne ?* orbital to favor overlap of the methyl-substituted terminus of the alkyne with the p?-orbital of the alkenyl fragment of the rhodacycle during alkyne insertion with PPh3 as the ligand. In contrast, the sterically demanding xyl-binap ligand cannot accommodate the analogous alkyne orientation, thereby forcing insertion to occur at the sterically preferred ester terminus, overriding the electronically preferred orientation for alkyne insertion.

SUBMITTER: Crandell DW

PROVIDER: S-EPMC5510011 | biostudies-literature | 2015 Dec

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

The origin of the ligand-controlled regioselectivity in Rh-catalyzed [(2 + 2) + 2] carbocyclizations: steric vs. stereoelectronic effects.

Crandell Douglas W DW Mazumder Shivnath S Evans P Andrew PA Baik Mu-Hyun MH

Chemical science 20150825 12

Density functional theory calculations demonstrate that the reversal of regiochemical outcome of the addition for substituted methyl propiolates in the rhodium-catalyzed [(2 + 2) + 2] carbocyclization with PPh3 and (S)-xyl-binap as ligands is both electronically and sterically controlled. For example, the ester functionality polarizes the alkyne π* orbital to favor overlap of the methyl-substituted terminus of the alkyne with the pπ-orbital of the alkenyl fragment of ...[more]

PMID: 28757978

Similar Datasets

Mechanistic insights into the gold-catalyzed cycloisomerization of bromoallenyl ketones: ligand-controlled regioselectivity.

Project description:Through computational and experimental studies, the mechanisms of gold-catalyzed cycloisomerization of bromoallenyl ketones in toluene have been elucidated. The divergent 1,2-migrations for the Au(I)- and Au(III)-catalyzed reactions have been investigated, and the results confirmed that the regiochemistry is ligand-dependent in cases of Au(PR3)L (L = Cl, OTf, BF4, and SbF6) catalysts.

| S-EPMC2435085 | biostudies-literature

Reciprocity of steric and stereoelectronic effects in the collagen triple helix.

Project description:In previous work, we demonstrated that 4-fluoroproline residues can contribute greatly to the conformational stability of the collagen triple helix, and that this stability arises from stereoelectronic effects that fix the pucker of the pyrrolidine ring and thereby preorganize the backbone properly for triple-helix formation. Here, we take a reciprocal approach, demonstrating that the steric effect of a 4-methyl group confers stability similar to that from a 4-fluoro group in the opposite configuration. Such fundamental interplay between steric and stereoelectronic effects is heretofore unknown in proteins-natural or synthetic-and provides a new means to modulate conformational stability.

| S-EPMC2517127 | biostudies-literature

Ligand steric contours to understand the effects of N-heterocyclic carbene ligands on the reversal of regioselectivity in Ni-catalyzed reductive couplings of alkynes and aldehydes.

Project description:The regioselectivities of N-heterocyclic carbene (NHC) ligands in Ni-catalyzed alkyne-aldehyde reductive coupling reactions with silane reducing agents are investigated using density functional theory. Reversal of regioselectivity can be achieved by varying the steric bulkiness of the ligand. The steric influences of NHC ligands are highly anisotropic. Regioselectivity is primarily controlled by the steric hindrance at the region of the ligand close to the alkyne. Analysis of 2D contour maps of the NHC ligands indicates that the regioselectivities are directly affected by the shape and orientation of the N-substituents on the ligand.

| S-EPMC3128454 | biostudies-literature

Stereoelectronic and steric effects in side chains preorganize a protein main chain.

Project description:Preorganization is shown to endow a protein with extraordinary conformational stability. This preorganization is achieved by installing side-chain substituents that impose stereoelectronic and steric effects that restrict main-chain torsion angles. Replacing proline residues in (ProProGly)(7) collagen strands with 4-fluoroproline and 4-methylproline leads to the most stable known triple helices, having T ( m ) values that are increased by > 50 degrees C. Differential scanning calorimetry data indicate an entropic basis to the hyperstability, as expected from an origin in preorganization. Structural data at a resolution of 1.21 A reveal a prototypical triple helix with insignificant deviations to its main chain, even though 2/3 of the residues are nonnatural. Thus, preorganization of a main chain by subtle changes to side chains can confer extraordinary conformational stability upon a protein without perturbing its structure.

| S-EPMC2818912 | biostudies-literature

Stereoelectronic effects determine oxacarbenium vs ?-sulfonium ion mediated glycosylations.

Project description:Activation of a glycosyl donor protected with a 2-O-(S)-(phenylthiomethyl)benzyl ether chiral auxiliary results in the formation of an anomeric ?-sulfonium ion, which can be displaced with sugar alcohols to give corresponding ?-glycosides. Sufficient deactivation of such glycosyl donors by electron-withdrawing protecting groups is, however, critical to avoid glycosylation of an oxacarbenium ion intermediate. The latter type of glycosylation pathway can also be suppressed by installing additional substituents in the chiral auxiliary.

| S-EPMC3076600 | biostudies-literature

Rh-catalyzed (5+2) cycloadditions of 3-acyloxy-1,4-enynes and alkynes: computational study of mechanism, reactivity, and regioselectivity.

Project description:The mechanism of Rh-catalyzed (5+2) cycloadditions of 3-acyloxy-1,4-enyne (ACE) and alkynes is investigated using density functional theory calculations. The catalytic cycle involves 1,2-acyloxy migration, alkyne insertion, and reductive elimination to form the cycloheptatriene product. In contrast to the (5+2) cycloadditions with vinylcyclopropanes (VCPs), in which alkyne inserts into a rhodium-allyl bond, alkyne insertion into a Rh-C(sp(2)) bond is preferred. The 1,2-acyloxy migration is found to be the rate-determining step of the catalytic cycle. The electron-rich p-dimethylaminobenzoate substrate promotes 1,2-acyloxy migration and significantly increases the reactivity. In the regioselectivity-determining alkyne insertion step, the alkyne substituent prefers to be distal to the forming C-C bond and thus distal to the OAc group in the product.

| S-EPMC3725470 | biostudies-literature

Complementary regioselectivity in Rh(III)-catalyzed insertions of potassium vinyltrifluoroborate via C-H activation: preparation and use of 4-trifluoroboratotetrahydroisoquinolones.

Project description:Potassium vinyltrifluoroborate was found to be an efficient partner with benzamide derivatives for Rh(III)-catalyzed annulations. 4-Trifluoroboratotetrahydroisoquinolones were generated under mild conditions, affording a regioisomerically complementary substitution pattern to other alkenes in related reactions. These new boron-containing building blocks were derivatized by N-arylations, retaining the boron substituent for further elaboration.

| S-EPMC3663910 | biostudies-literature

Rh-catalyzed regiodivergent hydrosilylation of acyl aminocyclopropanes controlled by monophosphine ligands.

Project description:A Rh-catalyzed regiodivergent hydrosilylation of acyl aminocyclopropanes has been developed. Acyl aminocyclopropanes were reacted with hydrosilanes in the presence of Rh catalysts to afford ring-opened hydrosilylated adducts through carbon-carbon (C-C) bond cleavage of the cyclopropane ring. The regioselectivity of the addition of silanes (linear or branched) can be switched by changing the monophosphine ligand. This C-C bond cleavage/hydrosilylation methodology is applicable to the synthesis of silanediol precursors.

| S-EPMC5436550 | biostudies-literature

A supramolecularly tunable chiral diphosphine ligand: application to Rh and Ir-catalyzed enantioselective hydrogenation.

Project description:A supramolecularly tunable chiral bisphosphine ligand bearing two pyridyl-containing crown ethers, (-) or (+)-Xyl-P16C6-Phos, was fabricated and utilized in the Rh-catalyzed asymmetric hydrogenation of ?-dehydroamino acid esters and Ir-catalyzed asymmetric hydrogenation of quinolines in high yields with excellent enantioselectivities (90-99% ee). Up to a 22% enhancement in enantioselectivity was achieved by the addition of certain amounts of alkali ions (Li+, Na+ or K+), which could be selectively recognized and effectively complexed by the crown ethers on the chiral Xyl-P16C6-Phos.

| S-EPMC6016442 | biostudies-literature

Stereoelectronic Effects Impact Glycan Recognition.

Project description:Recognition of distinct glycans is central to biology, and lectins mediate this function. Lectin glycan preferences are usually centered on specific monosaccharides. In contrast, human intelectin-1 (hItln-1, also known as Omentin-1) is a soluble lectin that binds a range of microbial sugars, including ?-d-galactofuranose (?-Galf), d-glycerol 1-phosphate, d-glycero-d-talo-oct-2-ulosonic acid (KO), and 3-deoxy-d-manno-oct-2-ulosonic acid (KDO). Though these saccharides differ dramatically in structure, they share a common feature-an exocyclic vicinal diol. How and whether such a small fragment is sufficient for recognition was unclear. We tested several glycans with this epitope and found that l-glycero-?-d-manno-heptose and d-glycero-?-d-manno-heptose possess the critical diol motif yet bind weakly. To better understand hItln-1 recognition, we determined the structure of the hItln-1·KO complex using X-ray crystallography, and our 1.59 Å resolution structure enabled unambiguous assignment of the bound KO conformation. This carbohydrate conformation was present in >97% of the KDO/KO structures in the Protein Data Bank. Bioinformatic analysis revealed that KO and KDO adopt a common conformation, while heptoses prefer different conformers. The preferred conformers of KO and KDO favor hItln-1 engagement, but those of the heptoses do not. Natural bond orbital (NBO) calculations suggest these observed conformations, including the side chain orientations, are stabilized by not only steric but also stereoelectronic effects. Thus, our data highlight a role for stereoelectronic effects in dictating the specificity of glycan recognition by proteins. Finally, our finding that hItln-1 avoids binding prevalent glycans with a terminal 1,2-diol (e.g., N-acetyl-neuraminic acid and l-glycero-?-d-manno-heptose) suggests the lectin has evolved to recognize distinct bacterial species.

| S-EPMC7392083 | biostudies-literature