An asymmetric induction principle and biomimetics with photons via electron transfer

Isoprenoid polyalkene radicals, formed upon anti-Markovnikov addition of a nucleophile to their parent radical cations, which are readily accessible v ia photoinduced electron transfer, undergo cascade cyclizations, The regios electivity is efficiently controlled by the substitution pattern, i. e. the generally observed 6-endo-trig mode is replaced by 5-exo-trig, if electron -deficient double bonds are involved. Mechanistic studies revealed that the se synthetically useful transformations, initiated by polyalkene radical ca tions being trapped by water, are propagated in a plain radical fashion and terminated upon either protonation of carbanions or hydrogen transfer, Cyc lization products were used for a natural product total synthesis, i.e of s typoldione. Moreover, high asymmetric inductions in such transformations ha ve been achieved by the use of chiral spirocyclic dioxinones, derived from the auxiliary (-)-menthone, remotely located from the initiation site of th e cyclizations. These asymmetric photoinduced cyclizations are further exam ples of a more general enantiodivergent induction principle giving access t o enantiomerically pure polycyclic terpenoids of complementary chiralities by means of the single chiral auxiliary (-)menthone, Finally, the efficient application of solar radiation for photochemical purpose is demonstrated b y the use of flat collectors which in contrast to concentrating technologie s not only employ direct, but also diffuse radiation (the latter amounts to about 40% of the global radiation at central European latitude).