Application to natural products synthesis

Abstract: Cyclization of unsaturated ketyl radical anions, photochemically induced by electron transfer from triethylamine (NEt3) to unsaturated ketones, produced cyclopentanols or cyclohexanols. The cyclization reaction was regio-, stereo- and chemo- selective and gave high yields in cyclopentanols or cyclohexanols. Ketyl radical anions could also induce the ring opening of strained ring such as cyclopropanes, epoxides and 7-oxabicyclo[2.2.l]heptanes. Furthermore 3-azabicyclo[4.3.0]nonane skeletons were obtained by photoreductive cyclization of €,a-unsaturated p-ketoamides, and azaspiranic skeletons by treatment of unsaturated p-ketoamides or enaminoamides by Mn(0Ac)g. Application of these methodologies to natural products synthesis is described. Cyclization of &€-unsaturated radicals is a very fast process which leads to cyclopentylmethyl or cyclohexyl radicals. Formation of the cyclopentane ring is highly favored according to literature data (ref. 1) and Baldwin's rules (ref. 2). Convenient methods to prepare the starting radical involve the reduction of variou