Iminoyl Radical Cyclizations

There has been an explosion in the development of a-iminoyl radical cyclizations over the past decade, and a number of applications have appeared in the field of alkaloid total synthesis. Perhaps the most outstanding use of this chemistry is the... 

The Fukuyama group has developed a versatile indole synthesis that relies on cyclization of iminoyl radicals generated by addition of tri- -butylstannyl radicals to isonitriles. For example isonitrile 43 [4 steps from 7V-(o-iodophenyl)formamide] was converted to 44 in 71% overall yield as shown in Eq. (15) [31]. This reaction takes place via an iminoyl radical cyclization followed by tautomerization of the resulting imine. Indole 44 was a key intermediate in a synthesis of vincadifform-... 

The neuroexcitatory amino acid a-kainic acid, a popular testing ground for new pyrrolidine syntheses, has been prepared by a number of routes that involve free-radical cyclization reactions. Bachi has reported two approaches that involve iminoyl radical cyclizations. One enantioselective route is described in Scheme 6 [35]. Isonitrile 48 was prepared in 4 steps from 4-bromo-3-methyl-2-butenal dimethyl acetal, the key reaction being an enantioselective addition of tert-butyl oc-isocyanoacetate to an aldehyde mediated by Hiyashi s catalyst. Treatment of 48 with a catalytic... 

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