Recent Developments in Nucleophilic Radical Addition to Imines: the Key Role of Transition Metals and the New Porta Radical-Type Version of the Mannich and Strecker Reactions

Abstract

This review summarizes the interesting results obtained during the last decade in the radical aminoalkylation of a wide range of nucleophilic radicals (deriving from hydrocarbons, ethers, alcohols, halogenated derivatives and amides) promoted by transition metals. We focus on the two main procedures which recently yielded the most relevant results in this field: the dimethylzinc-air process and the new Porta reaction, based on the Ti(III)/hydroperoxide system. These protocols often provide competitive alternatives to classical landmark transformations, like the Mannich reaction and the Strecker synthesis. Moreover, a brief overview of other significant examples is given in the last section of the review.

Radical Addition to Iminium Ions and Cationic Heterocycles

“…These reactions have been dormant for a long time because of the poor electrophilicity of the imino group, but in the last decades, radical additions to imines have been investigated with increasing attention. The radical addition to imines and derivatives has been summarized in excellent articles by Friestad [57], Naito [58], Punta [59], and Miyabe [60]. Mechanistically, iminium species can be proposed to be the actual radical acceptors since Lewis acids are usually added to improve the results.…”

New Advances in Titanium-Mediated Free Radical Reactions

“…Nucleophilic radical addition to imines, iminium salts or hydrazones, mediated by transition metal salts such as manganese [ 27 ], copper [ 28 , 29 , 30 ], and zirconium [ 31 , 32 , 33 ], represents a valuable alternative to the classical ionic routes for the selective C-C bond formation and the synthesis of high added value polifunctional molecules [ 12 , 13 , 14 , 15 , 16 , 17 ]. This approach becomes even more intriguing if the transition metal is able to promote, in one-pot, the in situ formation of the imine followed by nucleophilic addition, in accordance with the multicomponent reaction (MCR) strategy.…”

“…In the last decade, important improvements in this filed have been achieved by combining radical chemistry with transition-metal catalysis, due to the key role of transition metal complexes both in promoting and highly controlling sophisticated free-radical synthetic routes [ 4 , 5 , 6 , 7 ]. This approach has been adopted for different applications, ranging from oxidative [ 8 , 9 , 10 ] and reductive [ 11 ] radical processes to the selective C-C and C-N bond formation [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], passing through living polymerization [ 20 , 21 , 22 ].…”

Semiconductors in Organic Photosynthesis

“…Recently, some reviews on this field have been published (Gambarotti, 2010;Pastori, 2009;Shiraishi, 2008;Anpo & Kamat, 2010). Herein we report some examples taken from the literature which can be used to take a view on the recent state of the art.…”