Catalytic asymmetric transformations of oxa- and azabicyclic alkenes.

Oxa- and azabicyclic alkenes can be readily activated by transition-metal complexes with facial selectivity, because of the intrinsic reactivity of strained bicyclic structures. Synthetically, these compounds are important synthons that offer an important platform for the construction of biologically/medicinally significant compounds with two or more stereocenters. This Review comprehensively compiles the diverse catalytic processes involving the enantioselective transformations of oxa- and azabicyclic alkenes. It has been organized according to reaction type, including asymmetric ring opening (ARO) reactions, hydrofunctionalizations, cycloadditions and C-H activation reactions. The ARO section has been subdivided based on the type of nucleophiles employed, and further subdivided based on the metal used, with a separate topic dedicated to asymmetric ring-opening metathesis. Lastly, the presentation of each method/group of reactions is accompanied by concise discussions on their advantages and limitations.

Rhodium-Catalyzed Enantioselective Isomerization of meso-Oxabenzonorbornadienes to 1,2-Naphthalene Oxides.

Herein we describe a rhodium-catalyzed enantioselective isomerization of meso-oxabicyclic alkenes to 1,2-naphthalene oxides. These potentially useful building blocks can be accessed in moderate to excellent yields with impressive enantioselectivities. Additionally, experimental findings supported by preliminary computations suggest that ring-opening reactions of bridgehead disubstituted oxabicyclic alkenes proceed through the intermediacy of these epoxides and may point to a kinetically and thermodynamically favored reductive elimination as the origin for the observed enantioselectivities.

Rhodium-Catalyzed Asymmetric Cycloisomerization and Parallel Kinetic Resolution of Racemic Oxabicycles.

While desymmetrizations by intermolecular asymmetric ring-opening reactions of oxabicyclic alkenes with various nucleophiles have been reported over the past two decades, the demonstration of an intramolecular variant is unknown. Reported herein is the first rhodium-catalyzed asymmetric cycloisomerization of meso-oxabicyclic alkenes tethered to bridgehead nucleophiles, thus providing access to tricyclic scaffolds through a myriad of enantioselective C-O, C-N, and C-C bond formations. Moreover, we also demonstrate a unique parallel kinetic resolution, whereby racemic oxabicycles bearing two different bridgehead nucleophiles can be resolved enantioselectively.

Catalysis with cycloruthenated complexes.

Cycloruthenated complexes have been studied extensively over the last few decades. Many accounts of their synthesis, characterisation, and catalytic activity in a wide variety of transformations have been reported to date. Compared with their non-cyclometallated analogues, cycloruthenated complexes may display enhanced catalytic activities in known transformations or possess entirely new reactivity. In other instances, these complexes can be chiral, and capable of catalysing stereoselective reactions. In this review, we aim to highlight the catalytic applications of cycloruthenated complexes in organic synthesis, emphasising the recent advancements in this field.

Rhodium-Catalyzed Enantioselective Synthesis of Oxazinones via an Asymmetric Ring Opening-Lactonization Cascade of Oxabicyclic Alkenes.

The rhodium-catalyzed asymmetric ring opening reaction of oxabicyclic alkenes is shown to be an efficient method for synthesizing chiral heterocycles. We demonstrate that the pairwise combination of chiral catalyst with chiral amino-acid-derived pronucleophiles results in a stereodivergent synthesis of diastereomeric hydroxyesters. A favorable conformational preference induces the subsequent lactonization of one diastereomer leading to the highly enantioselective synthesis of oxazinones.

Nickel-Catalyzed Intramolecular Arylcyanation for the Synthesis of 3,3-Disubstituted Oxindoles.

A nickel-catalyzed arylcyanation reaction for the synthesis of 3,3-disubstituted oxindoles has been developed. This method features a bench-stable precatalyst system and serves as an economical alternative to the existing palladium-catalyzed arylcyanations described to date. A wide scope of oxindole products were accessible in moderate to good yields, and the rich chemistry of the newly installed nitrile functional group was demonstrated in the synthesis of various oxindole derivatives.

Naphthalene Toxicity: Methemoglobinemia and Acute Intravascular Hemolysis.

Naphthalene poisoning is a rare form of toxicity that may occur after ingestion, inhalation, or dermal exposure to naphthalene-containing compounds such as mothballs. Clinically, patients present with acute onset of dark brown urine, watery diarrhea, and non-bloody bilious vomiting 48-96 hours after exposure. Vital sign abnormalities include fever, tachycardia, hypotension, and persistent pulse oximetry readings of 84%-85% despite oxygen supplementation. Laboratory workup demonstrates hyperbilirubinemia with indirect predominance, hemolytic anemia, methemoglobinemia, and renal dysfunction. Treatment options include supportive care, red cell transfusion, ascorbic acid, methylene blue, and N-acetylcysteine. We present a case of naphthalene toxicity in a 20-year-old autistic male, who improved with supportive care, red blood cell transfusion, and ascorbic acid.

Dearomative Indole Bisfunctionalization via a Diastereoselective Palladium-Catalyzed Arylcyanation.

The first Pd-catalyzed dearomative indole bisfunctionalization via a diastereoselective arylcyanation is reported. This method facilitates the formation of diverse indoline scaffolds bearing congested stereocenters with high levels of diastereoselectivity. This also represents the first example of a cyanation mechanism involving a 2° benzylic Pd(II) intermediate.