Diversity in the Synthesis of Functionalized Cyclohexene Oxide Derivatives by a Cycloaddition-Fragmentation Sequence from Benzene Oxide

A cycloaddition-fragmentation sequence from benzene oxide and a nitroso- or azo-dienophile was investigated as a tool for access to highly substituted cyclohexene oxide derivatives. Alkyl lithium-promoted fragmentation of the cycloadducts led to the cyclic derivatives after 1,4- or 1,2-addition of a second equivalent of the lithium reagent. New fragmentation processes were observed when using non-nucleophilic bases of highly hindered alkyl lithium reagents. All reactions proceeded with complete stereocontrol.

π-Facial selectivity in the Diels-Alder reaction of glucosamine-based chiral furans and maleimides

Furans derived from carbohydrate feedstocks are a versatile class of bio-renewable building blocks and have been used extensively to access 7-oxanorbornenes via Diels-Alder reactions. Due to their substitution patterns these furans typically have two different π-faces and therefore furnish racemates in [4 + 2]-cycloadditions. We report the use of an enantiopure glucosamine derived furan that under kinetic conditions predominantly affords the exo-product with a high π-face selectivity of 6.5 : 1. The structure of the product has been resolved unequivocally by X-ray crystallography, and a multi-gram synthesis (2.8 g, 58% yield) confirms the facile accessibility of this multifunctional enantiopure building block.

Intermolecular Diels-Alder Cycloadditions of Furfural-Based Chemicals from Renewable Resources: A Focus on the Regio- and Diastereoselectivity in the Reaction with Alkenes

A recent strong trend toward green and sustainable chemistry has promoted the intensive use of renewable carbon sources for the production of polymers, biofuels, chemicals, monomers and other valuable products. The Diels-Alder reaction is of great importance in the chemistry of renewable resources and provides an atom-economic pathway for fine chemical synthesis and for the production of materials. The biobased furans furfural and 5-(hydroxymethyl)furfural, which can be easily obtained from the carbohydrate part of plant biomass, were recognized as "platform chemicals" that will help to replace the existing oil-based refining to biorefining. Diels-Alder cycloaddition of furanic dienes with various dienophiles represents the ideal example of a "green" process characterized by a 100% atom economy and a reasonable E-factor. In this review, we first summarize the literature data on the regio- and diastereoselectivity of intermolecular Diels-Alder reactions of furfural derivatives with alkenes with the aim of establishing the current progress in the efficient production of practically important low-molecular-weight products. The information provided here will be useful and relevant to scientists in many fields, including medical and pharmaceutical research, polymer development and materials science.

Synthesis of Enantioenriched α,α-Difluoro-β-arylbutanoic Esters by Pd-Catalyzed Asymmetric Hydrogenation

Synthesis of optically active gem-difluorinated organic molecules attracts a great deal of interest due to their unique properties in pharmaceutical and agrochemical areas. Herein, a series of enantioenriched α,α-difluoro-β-arylbutanoic esters were prepared in high yields (83-99%) with moderate to excellent enantioselectivities (≤97:3 er) by palladium-catalyzed asymmetric hydrogenation.

Enantioselective synthesis of fluorinated branched allylic compounds via Ir-catalyzed allylations of functionalized fluorinated methylene derivatives

Introduction of the functionalized monofluorinated methylenes into the allylic fragment under Ir catalysis gave the fluorinated branched allyl products in good to high yields with excellent regio- and enantioselectivities.

Recent applications of ring-rearrangement metathesis in organic synthesis

Ring-rearrangement metathesis (RRM) involves multiple metathesis processes such as ring-opening metathesis (ROM)/ring-closing metathesis (RCM) in a one-pot operation to generate complex targets. RRM delivers complex frameworks that are difficult to assemble by conventional methods. The noteworthy point about this type of protocol is multi-bond formation and it is an atom economic process. In this review, we have covered literature that appeared during the last seven years (2008–2014).

Copper-catalyzed regioselective fluorination of allylic halides

Group activity: A novel copper-catalyzed fluorination of internal allylic bromides and chlorides has been developed by using Et3N⋅3 HF as the fluorine source. A functional group (FG) within the substrate is required to achieve the allylic fluorination, and a variety of secondary allylic fluoride compounds can be accessed in good yield with excellent regioselectivity.

Practical synthesis of 4,4,4-trifluorocrotonaldehyde: a versatile precursor for the enantioselective formation of trifluoromethylated stereogenic centers via organocatalytic 1,4-additions

The practical synthesis of 4,4,4-trifluorocrotonaldehyde (1) and its application to enantioselective 1,4-additions are described. The organocatalytic 1,4-addition of 1 with several nucleophiles such as heteroaromatics, alkylthiols and aldoximes afforded the corresponding products, each bearing a trifluoromethylated stereogenic center with high optical purity. A resulting product was converted into an MAO-A inhibitor, befloxatone.