Oxa bowls: studies toward hexaoxa-[6]-peristylane. Synthesis of a seco-derivative of hexaoxa-[6]-peristylane

Abstract

When the concept of equivalency of all-cis-[n]-formyl-[n]-cycloalkanes with [n]-oxa-[n]-peristylanes was followed, an approach to the "oxa bowl" hexaoxa-[6]-peristylane 4a was delineated. This required an access to all-cis-cyclohexane-hexacarbaldehyde 5, which could be subjected to a 6-fold intramolecular acetalization cascade. A readily available Diels-Alder adduct of cyclooctatetraene and maleic anhydride was chosen as the starting material and was elaborated to the endo, endo-tetraene 6 in which all the six aldehyde functionalities are present in a latent form with cis orientation in a locked cyclohexane ring. Although ozonolysis of 6 has so far led only to intractable products, the novelty and brevity of our approach have been demonstrated through the intramolecular acetalizations through ozonolysis in 7 and 15, leading to oxa bowls 9 (seco-hexaoxaperistylane) and 16, respectively. The formation of 9 and 16 requires the generation of five tetrahydrofuran and four oxacyclic rings, respectively, in a single-pot operation.