title: Synthetic Strategies for 5- and 6-Membered Ring Azaheterocycles Facilitated by Iminyl Radicals.
abstract: The totality of chemical space is so immense that only a small fraction can ever be explored. Computational searching has indicated that bioactivity is associated with a comparatively small number of ring-containing structures. Pyrrole, indole, pyridine, quinoline, quinazoline and related 6-membered ring-containing aza-arenes figure prominently. This review focuses on the search for fast, efficient and environmentally friendly preparative methods for these rings with specific emphasis on iminyl radical-mediated procedures. Oxime derivatives, particularly oxime esters and oxime ethers, are attractive precursors for these radicals. Their use is described in conventional thermolytic, microwave-assisted and UV-vis based preparative procedures. Photoredox-catalyzed protocols involving designer oxime ethers are also covered. Choice can be made amongst these synthetic strategies for a wide variety of 5- and 6-membered ring heterocycles including phenanthridine and related aza-arenes. Applications to selected natural products and bioactive molecules, including trispheridine, vasconine, luotonin A and rutaecarpine, are included.
authors.affiliation: University of St. Andrews, EaStCHEM School of Chemistry, St. Andrews, Fife KY16 9ST, UK. jcw@st-andrews.ac.uk.
authors.forename: John C
authors.initials: JC
authors.lastname: Walton
mesh_terms: D002384:Catalysis; D003500:Cyclization; D004149:Dioxoles / Q000138:chemical synthesis / Q000737:chemistry; D005609:Free Radicals / Q000138:chemical synthesis* / Q000737:chemistry; D026121:Indole Alkaloids / Q000138:chemical synthesis / Q000737:chemistry; D010091:Oximes / Q000737:chemistry*; D010617:Phenanthridines / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry; D011758:Pyrroles / Q000138:chemical synthesis / Q000737:chemistry; D011799:Quinazolines / Q000138:chemical synthesis / Q000737:chemistry*; D011809:Quinones / Q000138:chemical synthesis / Q000737:chemistry; D052999:Quinazolinones
chemical_list: D004149:Dioxoles; D005609:Free Radicals; D026121:Indole Alkaloids; D010091:Oximes; D010617:Phenanthridines; D011725:Pyridines; D011758:Pyrroles; D011799:Quinazolines; D011809:Quinones; C480761:luotonin A; C462033:trispheridine; C028632:rutecarpine; D052999:Quinazolinones; C023666:pyridine
keywords: heterocycles; natural products; organic synthesis; photoredox catalysis; radicals