Synthesis of hetero- and carbocycles by nucleophilic substitution at sp2 carbon

Intermolecular Sonogashira Coupling and Intramolecular 5-Exo-dig Cycloisomerization Cascade: A One-Pot Pathway for Accessing (3-Benzylbenzofuran-2-yl)(phenyl)methanones

Herein, we present an efficient and straightforward strategy enabling access to 2,3-disubstituted benzo[b]furans. The whole synthetic process proceeds via a domino intermolecular Sonogashira coupling of 2-(2-bromophenoxy)-1-phenylethan-1-ones/alkyl 2-(2-bromophenoxy)acetates/2-(2-bromophenoxy)acetonitrile/1-(2-bromophenoxy)propan-2-one with terminal acetylenes followed by an intramolecular carbanion-yne cyclization in a 5-exo-dig manner and subsequent double-bond isomerization. Notably, two C-C bonds have been constructed in a one-pot manner and a wide variety of (3-benzylbenzofuran-2-yl)(phenyl)methanones were accomplished with good functional group tolerance.

Recent synthesis of thietanes

Thietanes are important aliphatic four-membered thiaheterocycles that are found in the pharmaceutical core and structural motifs of some biological compounds. They are also useful intermediates in organic synthesis. Various synthetic methods of thietanes have been developed, including inter- and intramolecular nucleophilic thioetherifications, photochemical [2 + 2] cycloadditions, ring expansions and contractions, nucleophilic cyclizations, and some miscellaneous methods. The recently developed methods provide some new strategies for the efficient preparation of thietanes and their derivatives. This review focuses on the synthetic methods to construct thietane backbones developed during 1966 to 2019.

Shelf-Stable (E)- and (Z)-Vinyl-λ3-chlorane: A Stereospecific Hyper-vinylating Agent

We report the first stereoselective synthesis of stable (E)- and (Z)-β-chlorovinyl-λ³-chlorane via direct mesitylation of 1,2-dichloroethylene with mesityldiazonium tetrakis(pentafluorophenyl)borate under mild reaction conditions. The structure of the (E)-vinyl-λ³-chlorane was established by single-crystal X-ray analysis. Because of the enormously high leaving group ability of the aryl-λ³-chloranyl group, vinyl-λ³-chloranes undergo not only S_NVσ-type reaction with extremely weak nucleophiles such as perfluoroalkanesulfonate, iodobenzene, and aromatic hydrocarbons but also coupling with phenylcopper(I) species.

Three-dimensional heterocycles: new uracil-based structures obtained by nucleophilic substitution at the sp2 carbon of bromoisoxazoline

The regioisomeric cycloadducts of bromonitrile oxide and N-benzoyl-2,3-oxaza-norborn-5-ene were easily prepared and elaborated into a novel class of uracil-based scaffolds. The key-synthetic step is the nucleophilic substitution at the sp2 carbon atom of the bromoisoxazoline three-dimensional heterocycles. The protocol to perform the nucleophilic substitution of uracil anions was optimized and adapted to the steric requirements of the substrates. A library of pyrimidine derivatives was prepared in very good yields and the products were fully characterized. They are proposed as nucleoside analogues and as synthons for β-turn motifs within PNA structures.