Synthesis of angularly fused cyclopentanoids and analogous tricycles via photoinduced ketyl radical/radical anion fragmentation-cyclization reactions

Tzvetkov NT, Arndt T, Mattay J. Synthesis of angularly fused cyclopentanoids and analogous tricycles via photoinduced ketyl radical/radical anion fragmentation-cyclization reactions. TETRAHEDRON. 2007;63(42):10497-10510.Angular fused tricycles were synthesized through intramolecular tandem fragmentation-cyclization reactions by photochemically induced electron transfer (PET) of tricyclic alpha-cyclopropyl ketones with an unsaturated side chain at the position gamma to the carbonyl group. The reactions resulted in regioselective cleavage of a beta-cyclopropyl bond with formation of angular fused tricyclic ring systems via ketyl radical/radical anions as reactive intermediates. In general, triethylamine ( TEA) was used as a strong reducing reagent in acetonitrile. The preferred regioselectivity of the cyclization step (exo vs endo) depending on the substitution pattern at the quaternary carbon center (C beta') of the tricyclic alpha-cyclopropyl ketones was investigated. In addition, we also checked a two-step pathway for the synthesis of angular dioxa-triquinanes including photolysis of an allyloxy-substituted cyclopenta[ c] furanone derivative and subsequent beta-cleavage of the resulted dioxa-[4.5.5.5]fenestrane under reductive PET conditions. (c) 2007 Elsevier Ltd. All rights reserved