Synthesis of Cyclopentene Derivatives via Electrochemically Induced Intermolecular Selective (3+2) Annulation.

Cyclopentenes are common cores in many natural products, and in bioactive and functional molecules. However, their synthesis remains challenging in terms of harsh conditions, poor selectivity, prefunctionalization of the substrates, over-reliance on volatile activating reagents and the use of noble metals. Herein, we develop an electrochemical mediator-induced intermolecular selective (3+2) annulation of readily available alkenes and alkynes/alkenes, which provides a simple and efficient method for the synthesis of a library of decorated cyclopentenes and cyclopentanes. This protocol features high efficiency, mild reaction conditions, broad substrate scope, good functional group tolerance, and high regioselectivity. Potential applications are demonstrated by gram-scale synthesis as well as the construction of structural diversity and complexity. A preliminary mechanistic investigation was performed, which indicated that an iodine radical and carbon radicals are involved in this transformation.

Selective radical cascade (4+2) annulation with olefins towards the synthesis of chroman derivatives via organo-photoredox catalysis.

Due to the importance of chroman frameworks in medicinal chemistry, the development of novel synthetic methods for these structures is gaining increasing interest of chemists. Reported here is a new (4 + 2) radical annulation approach for the construction of these functional six-membered frameworks via photocatalysis. Featuring mild reaction conditions, the protocol allows readily available N-hydroxyphthalimide esters and electron-deficient olefins to be converted into a wide range of valuable chromans in a highly selective manner. Moreover, the present strategy can be used in the late-stage functionalization of natural product derivatives and biologically active compounds, which demonstrated the potential application. This method is complementary to the traditional Diels-Alder [4 + 2] cycloaddition reaction of ortho-quinone methides and electron-rich dienophiles, since electron-deficient dienophiles were smoothly transformed into the desired chromans.