Tandem β-Fragmentation−Hydrogen Abstraction Reaction of Alkoxy Radicals in Steroidal Systems
作者:Alicia Boto、Raimundo Freire、Rosendo Hernández、Ernesto Suárez、María S. Rodríguez
DOI:10.1021/jo962252h
日期:1997.5.1
have been prepared in order to test a newtandem beta-fragmentation-hydrogen abstraction reaction. The alkoxy radicals generated by irradiation of these alcohols with visible light in the presence of (diacetoxyiodo)benzene, iodine, and molecular oxygen undergo a beta-fragmentation reaction followed by peroxidation of the C-radical formed. The peroxy radical reacts further with iodine to give an alkoxy
A new sequential alkoxy radical fragmentation of δ-hydroxyketones
作者:Alicia Boto、Rosendo Hernández、Ernesto Suárez
DOI:10.1016/s0040-4039(00)77181-4
日期:1994.4
The alkoxy radicals formed by the reaction of steroidal cyclic hydroxyketones (1) and (2) with (diacetoxyiodo)benzene and iodine or mercuric oxide and iodine under oxygen atmosphere and irradiation with visible light undergo a new quintuple sequence beta-fragmentation-peroxidation-radical reduction-radical reduction-radical cyclization-beta-fragmentation reaction before being trapped by an atom of iodine.
Tandem Carbon-Radical Peroxidation-Addition to Carbonyl Groups Reaction. A New Synthesis of Steroidal .beta.-Peroxy Lactones
作者:Alicia Boto、Rosendo Hernandez、Ernesto Suarez、Carmen Betancor、Maria S. Rodriguez
DOI:10.1021/jo00130a020
日期:1995.12
A mild and efficient synthesis of beta-peroxy lactones by alkoxy radical beta-fragmentation reaction of gamma-hydroxy carbonyl compounds is described. Steroidal models 5-hydroxy-4-nor-3-oxa-5 alpha-cholestan-2-one (1), 5-hydroxy-5 alpha-cholestan-2-one (2), and 5,17 beta-dihydroxy-4-nor-5 alpha-androstan-2-one 17-acetate (3) were synthesized to test the present methodology. These substrates are subjected to photolysis with visible light in the presence of (diacetoxyiodo)benzene, lead tetraacetate, or HgO, I-2, and molecular oxygen to generate the corresponding alkoxy radical. The fragmentation of this radical results in the carbon radical which is trapped by molecular oxygen in the key step to generate a peroxy radical. Intramolecular addition of this peroxy radical to the carbonyl group present in the molecule is followed by beta-fragmentation to yield the peroxy lactone radical. Subsequent trapping of this radical results in stable peroxy lactone. In all cases, regiospecific beta-fragmentations and stereoselective peroxidation at C-10 radical were observed. This operationally simple multistep radical procedure permitted us to synthesize steroidal beta-peroxy lactones 8, 12, and 15 in moderate to good yields.