Addition of 2,3-Dihydro-5-furanyllithium to Diisopropyl Squarate as a Means for the Rapid Generation of Structurally Complex Oxygen- Containing Tetraquinane Networks.

Abstract The ability of 2,3-dihydro-5-furanyllithium (11) to trigger a reaction cascade when added to diisopropyl squarate (6) has been examined. Of particular concern were those experiments in which greater than 2 equiv of 11 were added to 6, as well when 1 equiv of 11 was added prior to or after an equiv of cyclopentenyllithium. The results shed light directly on such issues as whether the second vinyl anion adds cis or trans in reference to the first, and whether the bonding takes place in 1,2 or 1,4 fashion. Also revealed in the unsymmetrical case studies was whether protonation of the 1,3,5-cyclooctatriene intermediates occurs syn or anti to the adjacent proton and the extent to which this materialized at the “conventional” or the oxygen-substituted enolate site. In light of the fact that heterocyclic tetraquinanes containing five stereogenic centers are directly elaborated in one step from achiral building blocks, the transformations described in this work can be justifiably classified as “power reactions”.