Intramolecular anodic olefin coupling reactions: The use of allylsilane coupling partners with allylic alkoxy groups

Intramolecular anodic olefin coupling reactions having an alkoxy substituen t on the allylic carbon of an allylsilane moiety have been studied. These s ubstrates were examined as part of an effort to determine the compatibility of the anodic olefin coupling reaction with the presence of very acid-sens itive functional groups and the construction of functionalized five-membere d rings. In the initial experiment reported, an enol ether moiety was coupl ed to a trisubstituted allylsilane to afford a five-membered ring product w ithout loss of the allylic alkoxy group. The reaction was stereoselective a nd could be used to generate a five-membered ring with three contiguous asy mmetric centers. The stereochemical outcome of the reaction was best explai ned by a "pseudoequatorial" alkoxy group in the transition state; an argume nt that implied the reaction was under kinetic control. This suggestion was tested with the use of two electrolysis substrates that led to identical p roducts through different transition states. The two substrates led to much different product ratios, proving that the reactions were not controlled b y thermodynamics but rather governed by kinetic control. This observation w as opposite to the conclusion reached with earlier vinylsilane-based substr ates. Finally, the reactions were shown to be compatible with the presence of the alkoxy group even when challenged to form a fused bicyclic ring skel eton and a quaternary carbon. As in the initial case, the reaction to form a quaternary carbon was also highly stereoselective.