Visible light photocatalysis alkene-alkyne [2+2] cycloaddition by energy transfer

Abstract

Department of ChemistryThe alkyne-alkene [2+2] cycloaddition is straightforward approach to cyclobutene derivatives. Cyclobutenes are widely present in numerous natural products and pharmacological compounds with various biological properties. In addition, Structural characteristics of cyclobutene such as the high ring strain and unsaturation give the ability for many useful synthetic transformations. because the [2+2] cycloaddition is thermally forbidden, it can be achieved by photochemically. But this process has mostly been developed under UV light irradiation condition. The excited state of molecules has different reactivity from ground state. straightforward way to access the excited state of molecules is through a direct photoexcitation approach. Most organic molecules need high energy source for direct excitation such as UV light. But using high energy source like UV light has disadvantage for selectivity of the reaction, functional group resistance and general applicability. Recently, Visible light photocatalysis has attracted much attention from organic synthetic society because of its environmentally friendly and mild condition. Visible light mediated energy transfer process is a method to access excited (triplet) state in mild condition. Herein, we develop visible light photocatalysis [2+2] cycloadditions of alkene-alkyne by energy transfer mechanism. Under Blue LED light by using Iridium catalysts as photocatalyst, diverse cyclobutenes can be accessed in mild condition in moderated to excellent yields. Also, in intramolecular reaction, highly substituted 1,3-Dienes are observed by tandem intramolecular [2+2] cycloaddition - ring opening reaction. Moreover, further synthetic transformations to valuable structure like extended ??-systems were explored based on our synthesis method.clos