An approach toward the triquinane-type skeleton via reagent-controlled skeletal rearrangements. A facile method for protection-deprotection of organomercurials, tuning the selectivity of Wagner-Meerwein migrations, and a newroute to annulated lactones

Nonlinear triquinane-type building blocks have been synthesized using three strategic steps, namely, (1) Hg2+-mediated opening of a cyclopropane ring involving a skeletal rearrangement (3 --> 8), (2) an intramolecular organom etallic addition across a C=O bond triggered by activation of the C-HgX gro up by means of Me3CuLi2 (14 --> 26), and (3) selective, reagent-controlled skeletal rearrangements (43 --> 47 with Tl3+ or Hg2+; 43 --> 51 + 52 with P d2+; 44 --> 47 with Pd2+). A new method for protection/deprotection of orga nomercurials has been developed, which allows selective reduction of a carb onyl group with NaBH4 and other hydrides (8 --> 14 --> 16 --> 20) and Tebbe methylenation (14 --> 31 --> 32). Oxidative demercuration (8 --> 11 + 28) and Pd2+-catalyzed carbonylation of organomercurials (20 --> 53) allowed sy ntheses of gamma- and delta-lactones.