The synthesis of natural products using tandem radical sequences involving fragmentations
Radical fragmentation is a useful methodology in the synthesis of natural products containing medium-sized rings and tandem radical reactions allow the preparation of complex molecules in minimal steps. In this thesis, tandem fragmentation/oxygenation, fragmentation/elimination and fragmentation/fragmentation radical sequences involving [2+2] photoadduct derivatives were investigated as approaches to the synthesis of three classes of sesquiterpenoid natural products. A novel fragmentation/oxygenation sequence was attempted on a 5-4-5 photoadduct derivative as an approach to the synthesis of the guaianolide skeleton. Two approaches to the synthesis of dumortenol were attempted. The first approach was to involve the radical fragmentation/elimination of a difunctional 5-4-6 photoadduct derivative. A novel cyclobutylcarbinyl/cyclopropylcarbinyl radical fragmentation sequence was attempted on a 5/4/6/3 ring system as a second approach. A comparable fragmentation/fragmentation radical sequence involving the morestrained 5/4/5/3 ring system was then investigated as an approach to the synthesis of the lactarane skeleton.