Phase-Transfer-Catalyzed Alkylation of Hydantoins

Cycloadditions of 5-Vinyloxazolidine-2,4-diones: A Straightforward Access to the (Thio)hydantoin Scaffold

A palladium-catalyzed (3 + 2) cycloaddition between 5-vinyloxazolidine-2,4-diones (VOxD) and (thio)isocyanates is described. Under optimized conditions, an array of (thio)hydantoins was readily prepared, and an enantioselective version of this transformation was then studied. To illustrate the importance of this method, a concise synthesis of two bioactive compounds, nirvanol and mephenytoin, was carried out. This work emphasizes the synthetic potential of VOxD as useful precursors of zwitterionic aza-π-allylpalladiumII intermediates.

Allylation of cellulose microfibers for hydrosilylation with various hydrosilanes and hydrosiloxanes, and their application in corn-starch-mimosa tannin (CSMT) adhesive to improve particleboard properties

Recently, Cellulose microfibers (CMF) have garnered significant attention due to their renewability, biodegradability, and unique properties such as high aspect ratio, low density, high strength, stiffness, and distinctive optical properties. These characteristics have been highlighted in publications worldwide. However, the structure of CMF is difficult to access with solvents, limiting its dissolution in common organic solvents. The synthesis of CMF-siloxane or CMF-silane hybrid materials from cellulose generally involves several reactions steps, and therefore catalysts. The allylation of CMF is catalyzed by the phase-transfer catalyst tetrabutylammonium bromide (TBAB), which enables the combination of CMF with allyl. This is followed by a hydrosilylation reaction catalyzed by Karstedt's catalyst, based on platinum (0), to combine the hydrophilic allylated CMF with hydride-terminated hydrophobic hydrosilane or hydrosiloxane. Environmentally friendly particleboards were developed using bio-based adhesives composed of corn-starch and Mimosa tannin (CSMT) mixtures. These mixtures included 4, 6, 8, and 10 wt% of CMF, allylated CMF and silylated CMF. The mechanical and physical properties of particleboards, such as modulus of elasticity (MOE), modulus of rupture (MOR), internal bond strength (IB), surface soundness (SS), water absorption (WA) and thickness swelling (TS) were determined.

A Tunable Cascade Reaction of Ureidomalonates and Alkenyl Azlactones for the Divergent Synthesis of Hydantoins with Distinct Functional Groups

A tunable cascade reaction of ureidomalonates and alkenyl azlactones was disclosed, which gave rise to the construction of N-aroyl α-amino acid ester and imide-functionalized hydantoins in moderate to good yields and with excellent diastereoselectivities. The reaction pathway was precisely manipulated by organocatalysis and phase-transfer/sunlight relay catalysis, respectively, to realize the divergent synthesis. The successful gram-scale preparation of representative products exhibited the application potential of this protocol. Mechanistic studies indicated that the exchange and phase transfer of ethoxy anion played a key role in altering the reaction pathway, and sunlight might accelerate the oxidation process at the late stage of the reaction triggered by phase-transfer catalysis.

Chiral, air stable, and reliable Pd(0) precatalysts applicable to asymmetric allylic alkylation chemistry

Stereoselective carbon-carbon bond formation via palladium-catalyzed asymmetric allylic alkylation is a crucial strategy to access chiral natural products and active pharmaceutical ingredients. However, catalysts based on the privileged Trost and Pfaltz-Helmchen-Williams PHOX ligands often require high loadings, specific preactivation protocols, and excess chiral ligand. This makes these reactions uneconomical, often unreproducible, and thus unsustainable. Here we report several chiral single-component Pd(0) precatalysts that are active and practically-applicable in a variety of asymmetric allylic alkylation reactions. Despite the decades-long history and widespread use of Trost-type ligands, the precatalysts in this work are the only reported examples of stable, isolable Pd(0) complexes with these ligands. Evaluating these precatalysts across nine asymmetric allylic alkylation reactions reveals high reactivity and selectivity at low Pd loading. Importantly, we also report an unprecedented Pd-catalyzed enantioselective allylation of a hydantoin, achieved on gram scale in high yield and enantioselectivity with only 0.2 mol% catalyst.

Brønsted Base-Catalyzed Enantioselective α-Functionalization of Carbonyl Compounds Involving π-Extended Enolates

Chiral Brønsted base (BB) catalyzed asymmetric transformations constitute an important tool for synthesis. A meaningful fraction of these transformations proceeds through transiently generated enolate intermediates, which display quite versatile reactivity against a variety of electrophiles. Some years ago, our group became interested in developing BB-catalyzed asymmetric reactions of enolizable carbonyl substrates that involve π-extended enolates in which, besides control of reaction diastereo and enantioselectivity, the site-selectivity control is an additional issue in most cases. In the examples covered in this account the opportunities deployed, and the challenges posed, by these methods are illustrated, with a focus on the generation of quaternary carbon stereocenters. In the way, new bifunctional BB catalysts as well as achiral templates were developed that may find further applications.

A new synthetic ultrasound-assisted method for dibenzoepines

In this study, we have developed a new ultrasonic synthesis method of dibenzoepines using olanzapine and quetiapine, which are well-known drugs for the treatment of schizophrenia and bipolar disorder. The method is based on the N-alkylation reaction of the piperazine fragment in tricyclic compounds with methyl iodide or 2-(2-chloroethoxy)ethanol as the alkylating agent, respectively. The synthesis reactions were carried out in an ultrasonic bath with solvents such as acetonitrile or dimethylformamide in the presence of potassium or sodium carbonate or sodium hydroxide and metal-free, ecological phase transfer catalyst at a temperature of 40-50 °C. This allowed us to obtain olanzapine in 1 h (Y = 67%), and quetiapine in 3 h (Y = 72%). An ultrasonic reactor (Qsonica Q700) was used in the synthesis of olanzapine and made it possible to shorten the reaction time to 10 min and obtain 90% yield with very high purity. The developed method allows obtaining compounds in mild conditions and in a short time, thanks to which the process is more ecological than others described in the literature.

Organocatalytic cascade nucleophilic/aza-Michael addition reactions: metal-free catalytic strategy for the synthesis of hydantoins

Lewis base-catalyzed cascade nucleophilic/aza-Michael addition reaction of N-alkoxy β-oxo-acrylamides with isocyanates has been developed to afford various highly functionalized hydantoin derivatives in 80-98% yields under mild reaction conditions. The intriguing features of this method include metal-free reaction conditions, low catalyst loading, broad substrate scope and short reaction time.

Rigidified Bis(sulfonyl)ethylenes as Effective Michael Acceptors for Asymmetric Catalysis: Application to the Enantioselective Synthesis of Quaternary Hydantoins

The catalytic, enantio- and diastereoselective addition of hydantoin surrogates II to "rigidified" vinylidene bis(sulfone) reagents is developed, thus overcoming the inability of commonly employed β-substituted vinylic sulfones to react. Adducts are transformed in enantioenriched 5,5-disubstituted hydantoins through hydrolysis and reductive desulfonylation processes providing new structures for eventual bioassays. Density functional theory studies that rationalize the observed reactivity and stereoselectivity trends are also provided.