Reverse Regioselectivity in Reductive Ring Opening of Epoxide Enabled by Zirconocene and Photoredox Catalysis

A ring opening of epoxide with zirconocene and photoredox catalysis has been developed. Compared to the ring opening methods with titanocene, the present protocol exhibited reverse regioselectivity to afford more-substituted alcohols via putative less-stable radicals. DFT calculations indicated that the observed regioselectivity could be explained by shifting the transition states to more reactant-like structures by changing the metal center of the metallocene catalyst.

Reverse Regioselectivity in Reductive Ring Opening of Epoxide Enabled by Zirconocene and Photoredox Catalysis

A ring opening of epoxide with zirconocene and photoredox catalysis has been developed. Compared to the ring opening methods with titanocene, the present protocol exhibited reverse regioselectivity to afford more-substituted alcohols via putative less-stable radicals. DFT calculations indicated that the observed regioselectivity could be explained by shifting the transition states to more reactant-like structures by changing the metal center of the metallocene catalyst.

A Unified Total Synthesis of Isocyclocapitelline and Cyclocapitelline

A facile and concise synthesis of β-carboline alkaloids, such as (–)-isocyclocapitelline and (+)-cyclocapitelline, has been achieved from commercially available geraniol through a unified strategy. The key steps involved in this synthesis are Sharpless epoxidation, intramolecular ring opening of epoxide, Pictet-Spengler reaction, and dehydrogenative aromatization using 10% palladium/carbon in xylene under neutral conditions.

Catalyst Free, Nitromethane Assisted Facile Ring Opening of Epoxide with Less Reactive Aromatic Amines

<p>Nucleophilic ring opening reactions of epoxides with aromatic amines are in the forefront of the synthetic organic chemistry research to build new bioactive scaffolds. Here, a convenient, green and highly efficient regioselective ring opening of sterically hindered (2R,3S)-3-(<i>N</i>-Boc-amino)-1-oxirane-4-phenylbutane with various poorly reactive aromatic amines are accomplished under microwave irradiation in nitromethane. All the reactions effectively implemented for various aromatic amines involves reuse of nitromethane that supports its dual role as a solvent and catalyst. The corresponding new β-alcohol analogs of hydroxyethylamine (HEA) are isolated in 41-98% yields. The reactions proceed under mild conditions for a broad range of less reactive and sterically hindered aromatic amines. Proton NMR and UV-visible spectroscopic studies suggest that the nucleophilicity of amines is influenced by nitromethane, which is substantiated by the extensive computational studies. Overall, this methodology elucidates the first time use of nitromethane as a solvent for the ring opening reactions under microwave conditions involving equimolar ratio of epoxide and aromatic amine without any catalyst, facile ring opening of complex epoxide by less reactive aromatic amines, low reaction time, less energy consumption, recycling of the solvent and simple workup procedures.</p>

Catalyst Free, Nitromethane Assisted Facile Ring Opening of Epoxide with Less Reactive Aromatic Amines

<p>Nucleophilic ring opening reactions of epoxides with aromatic amines are in the forefront of the synthetic organic chemistry research to build new bioactive scaffolds. Here, a convenient, green and highly efficient regioselective ring opening of sterically hindered (2R,3S)-3-(<i>N</i>-Boc-amino)-1-oxirane-4-phenylbutane with various poorly reactive aromatic amines are accomplished under microwave irradiation in nitromethane. All the reactions effectively implemented for various aromatic amines involves reuse of nitromethane that supports its dual role as a solvent and catalyst. The corresponding new β-alcohol analogs of hydroxyethylamine (HEA) are isolated in 41-98% yields. The reactions proceed under mild conditions for a broad range of less reactive and sterically hindered aromatic amines. Proton NMR and UV-visible spectroscopic studies suggest that the nucleophilicity of amines is influenced by nitromethane, which is substantiated by the extensive computational studies. Overall, this methodology elucidates the first time use of nitromethane as a solvent for the ring opening reactions under microwave conditions involving equimolar ratio of epoxide and aromatic amine without any catalyst, facile ring opening of complex epoxide by less reactive aromatic amines, low reaction time, less energy consumption, recycling of the solvent and simple workup procedures.</p>

Phosphonium-Based Porous Ionic Polymer with Hydroxyl Groups: A Bifunctional and Robust Catalyst for Cycloaddition of CO2 into Cyclic Carbonates

The integration of synergic hydrogen bond donors and nucleophilic anions that facilitates the ring-opening of epoxide is an effective way to develop an active catalyst for the cycloaddition of CO2 with epoxides. In this work, a new heterogeneous catalyst for the cycloaddition of epoxides and CO2 into cyclic carbonates based on dual hydroxyls-functionalized polymeric phosphonium bromide (PQPBr-2OH) was presented. Physicochemical characterizations suggested that PQPBr-2OH possessed large surface area, hierarchical pore structure, functional hydroxyl groups, and high density of active sites. Consequently, it behaved as an efficient, recyclable, and metal-free catalyst for the additive and solvent free cycloaddition of epoxides with CO2. Comparing the activity of PQPBr-2OH with that of the reference catalysts based on mono and non-hydroxyl functionalized polymeric phosphonium bromides suggested that hydroxyl functionalities in PQPBr-2OH showed a critical promotion effect on its catalytic activity for CO2 conversion. Moreover, PQPBr-2OH proved to be quite robust and recyclable. It could be reused at least ten times with only a slight decrease of its initial activity.

Salalen vs. thiolen: in the ring(-opening of epoxide and cyclic carbonate formation)

A range of Fe(iii)-salalen and -thiolen–chloride complexes have been prepared and are shown to be active catalysts for the selective coupling of CO2 and cyclohexene oxide (CHO).

Active Copper Catalyzed Regioselective Ring Opening of Epoxides by Heterocyclic Amines: An Efficient Protocol for Synthesis of β-Amino Alcohols

The regioselective epoxide ring opening at less substituted carbon atom of epoxide were reported by nucleophiles like heterocyclic amines which gives well known 1,2-difunctionalized amino alcohols. These are present in many synthetic as well as natural products. The ring opening of epoxide is achieved by cleavage with amines in presence of copper(0) as a catalyst. It is observed that the lithium napthalenide reduction of copper(I) produces a highly reactive form of copper(0) that acts as a catalyst for ring opening of epoxides with an amine.