Abstract
A visible-light photoredox functionalization of 3,4-dihydro-1,4-benzoxazin-2-ones through a Friedel-Crafts reaction with indoles using an inexpensive organophotoredox catalyst is described. The reaction uses a dual catalytic system that is formed by a photocatalyst simple and cheap, 9,10-phenanthrenedione, and a Lewis acid, Zn(OTf)2. 5W white LEDs are used as visible-light source and oxygen from air as a terminal oxidant, obtaining the corresponding products with good yields. The reaction can be extended to other electron-rich arenes. Our methodology represents one of the most valuable and sustainable approach for the functionalization of 3,4-dihydro-1,4-benzoxazin-2-ones, as compared to the reported procedures. Furthermore, several transformations were carried out, such as the synthesis of the natural product cephalandole A and a tryptophol derivative.
Highlights
Visible-light is a safe, renewable, abundant, inexpensive, and non-polluting source of energy, which means that sunlight is the most “green” energy source that we can use
The development of methodologies to increase the use of visible-light to control chemical reactivity and achieve molecular complexity with higher levels of efficiency have become a hot topic in the last years and many challenging organic reactions have been described [3,4,5,6,7,8,9]
In order to improve the yield of 3aa, we decided to investigate a dual catalytic protocol combining
Summary
Visible-light (sunlight) is a safe, renewable, abundant, inexpensive, and non-polluting source of energy, which means that sunlight is the most “green” energy source that we can use. The development of methodologies using visible-light has become one of the greatest challenges in the scientific community in the last century [1,2] In this context, the development of methodologies to increase the use of visible-light to control chemical reactivity and achieve molecular complexity with higher levels of efficiency have become a hot topic in the last years and many challenging organic reactions have been described [3,4,5,6,7,8,9]. Some of the organophotoredox catalysts are expensive, such as pyrilium [14,15,16,17,18]
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