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spectroscopy. Iminyls with suitably placed arene or heteroarene acceptors underwent cyclisations yielding phenanthridine-type products from ortho-additions. For benzofuran and benzothiophene acceptors, spiro-cyclisation predominated at low temperatures, but thermodynamic control ensured ortho-products
(R)=N• closures are well documented. Forrester and co-workers were probably the first to utilise iminyl radicals synthetically. They obtained iminyls by persulfate oxidation of imino-oxyacetic acids in aqueous solvents and prepared azines [6], N-heterocycles [7][8], and other derivatives [9]. This
research initiated spiralling interest by synthetic chemists in iminyl radical-mediated preparations. Recently iminyls have been generated from quite a variety of precursors [10][11][12][13][14][15], and their cyclisations onto arenes [16][17][18][19][20][21] and heteroarenes [22][23][24] have attracted
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processes.
Keywords: amidyls; iminyls; radical allylation; radical vinylation; xanthate transfer; Introduction
Natural products exhibit an astonishing diversity of molecular architectures and structural complexity. This has spurred the development of numerous synthetic strategies for the rapid assembly of
creation of C–N bonds and for the synthesis of alkaloids is enormous [6]. One possible explanation is the lack, hitherto, of mild yet general methods for the generation of the various types of nitrogen radicals: aminyls, aminiums, iminyls, amidyls, carbamyls, ureidyls, etc.
We discovered some years ago
powder in combination with acetic acid can be extended to the production of iminyls by reduction of oxime esters [72][73]. This variant allows an easy access to pyrrolenines as underscored by the synthesis of complex structure 173 from thebain-derived oxime pivalate 171 via iminyl radical 172 (Scheme 32
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Graphical Abstract
Scheme 1:
Key radical step in the total synthesis of (–)-dendrobine.