Organic chemistry.(natural product synthesis)

Radical-mediated reactions provide opportunities in natural product synthesis. It is almost as if nature itself has pre-ordained many of its dauntingly complicated polycyclic and polyaromatic architectures to suit this methodology, and, at least in cases such as phenolic coupling, the radical approach is also the natural route. The problem of axial chirality in highly substituted biaryl target structures succumbs well to the biomimetic approach, and a nice example (see Figure 1) is provided by Bringmann and Tasler who have obtained single atropisomers by oxidative coupling of the aromatic rings, and take the important step of resolving the products to define their chiroptical properties. For the systems examined, DTBP, Pb[(OAc).sub.4], [Ag.sub.2]O and PhI[([O.sub.2][CCF.sub.3]).sub.2] proved particularly suited as oxidants (Tetrahedron, 2001, 57, 331). The same issue of Tetrahedron, which concentrates heavily on phenolic coupling in synthesis, provides details of a polymer-supported version of the popular hyp ervalent iodine oxidant (H Tohma, H Morioka, S Takizawa, M Arisawa and Y Kita, ibid, 345). Oxidation by hypervalent iodine forms a radical …