No abstract

The radical cascade protocol of the α-cyano α-TMS/aryl-capped alkynyl aryl ketones promoted by tert-butyl hydroperoxide under catalysis with tetrabutylammonium iodide in refluxing benzene has been developed, leading to the construction of a variety of highly functionalized [6,6,5] tricyclic frameworks in an efficient manner.

Making use of temperature-controlled thiation as a key operation, a simple route to 2-aminothiophenes or thieno­[2,3-c]­isothiazoles has been newly developed wherein the 2-aminothiophene nucleus was formed through an initial formation of thioamide followed by a 5-exo-dig addition to the tethered alkyne; however, under harsher thermal conditions, excess sulfur-transferring reagents enabled further oxidative thiation to generate the corresponding thieno­[2,3-c]­isothiazoles.

A convenient and general approach for cyclopenta[b]naphthalene derivatives containing a structurally diverse functionality at C‐4 position has been successfully developed, whereby manganese(III) acetate plays a key role to facilitate the tandem 5‐exo‐dig and 6‐exo/endo cyclization in an efficient manner. Various functional groups, including trimethyl silyl, aryl, ester, ketone, secondary/tertiary amide, phosphonate and halogen, capped on the terminal acetylenic unit are well tolerated under optimal reaction conditions. It is highly conceivable that this novel [6.6.5] framework formation procedure may have broad synthetic utility in light of its operational simplicity and high yields.

We have developed a new and general approach to construct a variety of benzo[b]fluorene and cyclopenta-[b]naphthalene derivatives via the palladium(0)/copper(I)-catalyzed tandem cyclization of aryl 1-cyanoalk-5-ynyl ketone systems in an extremely efficient manner. The key operation lies in the copper(I)-catalyzed aerobic oxidation, which allows for activation of two successive intramolecular cycloadditions immediately after the Sonogashira coupling reaction has occurred.