Highly stereoselective Friedel–Crafts alkylations of unactivated benzenes by episulfonium ion cyclizations

Carbosulfenylation of Alkenes with Organozinc Reagents and Dimethyl(methylthio)sulfonium Trifluoromethanesulfonate

The electrophilic alkylthiolation of alkenes, initiated by dimethyl(methylthio)sulfonium salts and the subsequent addition of various heteronucleophilies has been well-established. Regarding the use of carbon nucleophiles, however, only carefully designed sp-type carbon sources have been successfully applied. We herein present our findings on the methylthiolation of alkenes with dimethyl(methylthio)sulfonium trifluoromethanesulfonate, followed by carbon-carbon bond formation in the presence of organozinc reagents, thus achieving a catalyst-free protocol toward to the carbosulfenylation of alkenes.

FeCl3-Catalyzed Regio-Divergent Carbosulfenylation of Unactivated Alkenes: Construction of a Medium-Sized Ring

A FeCl₃-catalyzed regio-divergent carbosulfenylation of unactivated alkenes with electrophilic N-sulfenophthalimides has been developed. This protocol provides a straightforward and efficient access to various medium-sized rings, especially strained 7- and 8-membered carborings with a sulfur atom attached. The endo/exo selectivity in the reaction depends on the atom number of the chain between arene and alkene. Broad substrate scope, high yields, and gram-scale synthesis exemplified the utility and practicability of this protocol. In addition, this methodology can be extended to the carboselenylation of isolated alkenes.

Schweinfurthins A–Q: isolation, synthesis, and biochemical properties

Stilbene analogues have shown remarkable structural diversity constituting simple or tangled structures, which have attracted the synthetic as well as the medicinal chemistry communities. Schweinfurthins are a family of prenylated/geranylated/farnesylated stilbenes that are isolated from an African plant belonging to the Macaranga species. These compounds have displayed potency towards central nervous system, renal and breast cancer cell lines. Specifically, these compounds have been found to be potent and selective inhibitors of cell growth in the National Cancer Institute's 60 cell-line screen. In this review article, we described the isolation, synthesis, and biochemical properties of schweinfurthins.

An overview of the isolation, synthesis, and biochemical properties of the stilbene-based natural products schweinfurthins A–Q (1999–2017).

Catalytic, enantioselective, intramolecular carbosulfenylation of olefins. Preparative and stereochemical aspects

The first catalytic, enantioselective, intramolecular carbosulfenylation of isolated alkenes with aromatic nucleophiles is described. The combination of N-phenylsulfenylphthalimide, a chiral selenophosphoramide derived from BINAM, and ethanesulfonic acid as a cocatalytic Brønsted acid induced an efficient and selective cyclofunctionalization of various alkenes (aliphatic and aromatic) tethered to a 3,4-methylenedioxyphenyl ring. Under these conditions, 6-phenylthio-5,6,7,8-tetrahydronaphthalenes are formed diastereospecifically in good yields (50-92%) and high enantioselectivities (71:29-97:3 er). E-Alkenes reacted much more rapidly and with much higher selectivity than Z-alkenes, whereas electron-rich alkenes reacted more rapidly but with comparable selectivity to electron-neutral alkenes and electron-deficient alkenes. The Brønsted acid played a critical role in effecting reproducible enantioselectivity. A model for the origin of enantioselectivity and the dependence of rate and selectivity on alkene structure is proposed along with a rationale for the site selectivity in reactions with monoactivated arene nucleophiles.

Catalytic, enantioselective, intramolecular carbosulfenylation of olefins

The first catalytic, enantioselective carbosulfenylation of alkenes with an aromatic nucleophile is described, using a BINAM-based selenophosphoramide catalyst. E-Alkyl- and aryl-substituted alkenes afforded tetrahydronaphthalenes with complete diastereospecificity, and generally high enantiomeric ratios.

Synthesis of nonracemic 3-deoxyschweinfurthin B

Synthesis of nonracemic 3-deoxyschweinfurthin B has been accomplished through a synthetic sequence including a key cascade cyclization of an epoxy olefin. The intermediate epoxide could be prepared as a single enantiomer through an AD-mix-alpha (or AD-mix-beta) oxidation, and the stereochemistry of the epoxide has been shown to control formation of the two additional stereogenic centers created through the cyclization. Synthetic 3-deoxyschweinfurthin B was found to have potent differential activity in the National Cancer Institute's 60 cell line anticancer assay. This represents the first synthesis of the tetracyclic schweinfurthin skeleton, validating our overall synthetic strategy and providing the first schweinfurthin analogue with activity slightly greater than those of the natural products.