Béatrice Quiclet-Sire

Fun with radicals: Some new perspectives for organic synthesis*

The degenerative radical addition-transfer of xanthates onto alkenes allows the rapid assembly of richly functionalized structures. Various families of open-chain, cyclic, and polycyclic compounds can thus be readily accessed. Furthermore, the process can be extended to the synthesis or modification of aromatic and heteroaromatic derivatives by exploiting the possibility of using peroxides both as initiators and stoichiometric oxidants. The modification of existing polymers and the controlled synthesis of block polymers by what is now known as the RAFT/MADIX (reversible addition–fragmentation transfer/macromolecular design by interchange of xanthate) process is described briefly.

The Total Synthesis of (±)‐Fortucine and a Revision of the Structure of Kirkine

Lycorine alkaloids are isolated from the Amaryllidaceae species of plants, and their medicinal value has an old and rich history dating back to ancient Greece. Members of the lycorine alkaloids possess antineoplastic, antimitotic, insect antifeedant, and antiviral activities; they also inhibit growth and cell division in higher plants, protein and DNA synthesis in murine cells, and in vivo growth of a murine transplantable ascite tumor. The tetracyclic pyrrolo[d,e]phenanthridine (galanthan) framework that characterizes the lycorine alkaloids has been the subject of intense synthetic scrutiny ever since the structure of lycorine itself was established in 1955. While the great majority of the these alkaloids have a trans B/C-ring junction, there are a few compounds with a cis B/C-ring junction; for example, g-lycorane (1), fortucine (2), and siculinine (3 ; Scheme 1).

Synthesis of substituted naphthalenes from α-tetralones generated by a xanthate radical addition–cyclisation sequence

A simple, highly efficient and cheap synthesis of substituted naphthalenes is reported. These aromatic compounds can be easily prepared in acidic or basic conditions from [small alpha]-tetralones, obtained by a xanthate-mediated addition-cyclisation sequence.

A new synthesis of pyrroles

The radical reaction between an N-ethylsulfonylenamide and an alpha-xanthyl ketone gives an intermediate gamma-keto imine which spontaneously ring-closes to the pyrrole.

A practical access to α-phosphonoenamides

Abstract Reaction of α-oximinophosphonates first with acetic anhydride then with iron powder and acetic acid at 50–60xa0°C results in the clean formation of an E – Z mixture of α-phosphonoenacetamides, which are immediate precursors to α-aminophosphonic acids.

A convergent approach to 2-substituted-5-methoxyindoles. Application to the synthesis of melatonin

A convergent, radical based synthesis of 5-methoxyindoles including melatonin is described.

A practical access to acyl radicals from acyl hydrazides.

Various acyl radicals can be generated from the corresponding acyl triphenylmethyldiazo derivatives, produced by in situ oxidation of hydrazide precursors with phenylseleninic acid.

An expedient synthesis of homophthalimides

The six-membered heterocyclic subunit of homophthalimides can be obtained by a direct, hitherto unprecedented, radical cyclisation onto an aromatic ring starting from a xanthate precursor.

α-Scission of sulfonyl radicals: a versatile process for organic synthesis

The reversible addition of aliphatic radicals to sulphur dioxide can be exploited to design a variety of tin-free chain reactions. This brief review summarises some of the possibilities, namely radical allylation, vinylation, alkynylation, and azidation of various substrates.

Some aspects of radical cascade and relay reactions

The ability to create carbon–carbon bonds is at the heart of organic synthesis. Radical processes are particularly apt at creating such bonds, especially in cascade or relay sequences where more than one bond is formed, allowing for a rapid assembly of complex structures. In the present brief overview, examples taken from the authors laboratory will serve to illustrate the strategic impact of radical-based approaches on synthetic planning. Transformations involving nitrogen-centred radicals, electron transfer from metallic nickel and the reversible degenerative exchange of xanthates will be presented and discussed. The last method has proved to be a particularly powerful tool for the intermolecular creation of carbon–carbon bonds by radical additions even to unactivated alkenes. Various functional groups can be brought into the same molecule in a convergent manner and made to react together in order to further increase the structural complexity. One important benefit of this chemistry is the so-called RAFT/MADIX technology for the manufacture of block copolymers of almost any desired architecture.