Asymmetric Synthesis of α-Spiro-γ-lactones and α-Substituted γ-Lactones via Chiral Bifunctional Sulfide-Catalyzed Bromolactonizations

An efficient enantioselective synthesis of γ-chiral α-spiro-γ-lactones, which are important building blocks for pharmaceuticals, was achieved via BINOL-derived chiral bifunctional sulfide-catalyzed bromolactonizations of α-allyl carboxylic acids containing either hetero- or carbocyclic structures. Transformations of the resultant α-spiro-type bromolactonization product were examined to obtain optically active γ-functionalized α-spiro-γ-lactones. The utility of this catalytic system was also demonstrated in the asymmetric synthesis of α,α-diaryl- and dialkyl-substituted γ-lactones.

Recent Advances in the Oxone-Mediated Synthesis of Heterocyclic Compounds

Oxone is a commercially available oxidant, composed of a mixture of three inorganic species, being the potassium peroxymonosulfate (KHSO5) the reactive one. Over the past few decades, this cheap and environmentally friendly oxidant has become a powerful tool in organic synthesis, being extensively employed to mediate the construction of a plethora of important compounds. This review summarizes the recent advances in the Oxone-mediated synthesis of N-, O- and chalcogen-containing heterocyclic compounds, through a wide diversity of reactions, starting from several kinds of substrate, highlighting the main synthetic differences, advantages, the scope and limitations.

Halogen-Induced Controllable Cyclizations as Diverse Heterocycle Synthetic Strategy

In organic synthesis, due to their high electrophilicity and leaving group properties, halogens play pivotal roles in the activation and structural derivations of organic compounds. Recently, cyclizations induced by halogen groups that allow the production of diverse targets and the structural reorganization of organic molecules have attracted significant attention from synthetic chemists. Electrophilic halogen atoms activate unsaturated and saturated hydrocarbon moieties by generating halonium intermediates, followed by the attack of carbon-containing, nitrogen-containing, oxygen-containing, and sulfur-containing nucleophiles to give highly functionalized carbocycles and heterocycles. New transformations of halogenated organic molecules that can control the formation and stereoselectivity of the products, according to the difference in the size and number of halogen atoms, have recently been discovered. These unique cyclizations may possibly be used as efficient synthetic strategies with future advances. In this review, innovative reactions controlled by halogen groups are discussed as a new concept in the field of organic synthesis.

Chemoenzymatic Halocyclization of γ,δ-Unsaturated Carboxylic Acids and Alcohols

A chemoenzymatic method for the halocyclization of unsaturated alcohols and acids by using the robust V-dependent chloroperoxidase from Curvularia inaequalis (CiVCPO) as catalyst has been developed for the in situ generation of hypohalites. A broad range of halolactones and cyclic haloethers are formed with excellent performance of the biocatalyst.

Chiral selenide-catalyzed enantioselective synthesis of trifluoromethylthiolated 2,5-disubstituted oxazolines

Chiral selenide-catalyzed enantioselective trifluoromethylthiolation of 1,1-disubstituted alkenes is disclosed. By this method, a variety of chiral trifluoromethylthiolated 2,5-disubstituted oxazolines were obtained in good yields with high enantioselectivities. This work not only provides a new pathway for the synthesis of chiral oxazolines, but also expands the library of chiral trifluoromethylthiolated molecules.

Access to Alkyl-Substituted Lactone via Photoredox-Catalyzed Alkylation/Lactonization of Unsaturated Carboxylic Acids

An efficient photoredox-catalyzed alkylation/lactonization reaction of unsaturated carboxylic acids by using alkyl N-hydroxyphthalimide esters as alkylation reagents has been developed. Varieties of redox-active esters derived from aliphatic carboxylic acids were proved viable in this method, affording alkyl substituted lactones in moderate to good yields. This redox-neutral procedure features mild conditions and operational simplicity, which provides a new strategy for the synthesis of alkyl substituted lactones.

Radical-mediated synthesis of γ-lactones by copper-catalyzed intermolecular carboesterification of alkenes with α-carbonyl alkyl bromides and H2O

A novel copper-catalyzed intermolecular carboesterification strategy of alkenes with α-carbonyl alkyl bromides is described.

Catalytic dehydrogenative dual functionalization of ethers: dealkylation–oxidation–bromination accompanied by C–O bond cleavage via aerobic oxidation of bromide

Catalytic dehydrogenative dual functionalization (DDF) of ethers via oxidation, dealkylation, and α-bromination by the aerobic oxidation of bromide was developed to obtain the corresponding α-bromo ketones in high yields.

Magnesium Lewis Acid Assisted Oxidative Bromoetherification Involving Bromine Transfer from Alkyl Bromides with Aldehydes by Umpolung of Bromide

An oxidative bromoetherification involving a bromine transfer from alkyl bromides upon reacting them with aldehydes in a Grignard reaction with a concurrent oxidation of bromide was developed to provide substituted tetrahydrofurans in high yields. This reaction, which proceeds through two types of bromine transfer, was promoted by the addition of a Brønsted acid. Mechanistic studies suggested that a magnesium Lewis acid activates hypobromate, which is generated in situ from the reaction of bromide and Oxone to improve the electrophilicity of the bromonium ion (Br(+) ) for the oxidative bromoetherification of alkenyl alcohols. Furthermore, the magnesium Lewis acid catalyzed oxidative bromoetherification of an alkenyl alcohol proceeded to provide a cyclization product in 92 % yield.