(–)-Norzoanthamine
A synthesis combining radical methods old and new
Free radicals! Everything about them sounds scary and extreme – and for a long time it was. In the early days of radical chemistry, high temperatures, UV light and dissolving metals were the only way to get at these often highly reactive intermediates. These days, while these species are still a bogeyman in adverts for many dubious health products, they have become an indispensable tool to the modern synthetic chemist. One can only imagine the dismay of radical chemistry pioneer Moses Gomberg, who tried to reserve their study for himself back in 1901.
During my PhD studies, I ran a range of textbook radical reactions, including Birch-type reductions, benzylic brominations and even some organotin chemistry, which I can still smell to this day. These were typical old-school radical reactions – that is to say, fairly dangerous and unappealing. However, in the 10 years or so since I completed my graduate education, some of the hottest areas of research in organic synthesis have been those that allow us to more easily generate and harness open-shell species, which is the essence of most photoredox catalysis. With modern methods to generate radicals, compute bond strengths and explain their reactivity, we can now leverage these reactive but predictable species to perform powerful and unique chemistry – without getting sunburn from mercury lamps or having to bleach tin off all of our glassware!