Synthetic studies towards prismanes: 1,4-bishomo-[6]-prismane ("garudane")

Abstract

The first synthesis of 1,4-bishomohexaprismane 6, the true, face-to-face, heptacyclic dimer of norbornadiene ia delineated. In the initial phase, the readily available norborneno-p-benzoquinone 13 was transformed into the bishomoseco[7]-prismane dione 11 in three steps involving stereoselective 4+2 cycloaddition, regio- and stereoselective Ti³⁺ reduction of the enedione moiety and intramolecular 2+2-photocycloaddition. The versatile dione 11 through Favorskii ring contraction technology and subsequent functional group interconversions delivered the target hydrocarbon 6. The new synthetic methodology outlined here opens up avenues for the synthesis of many novel polyhedranes, in particular [6]-, [7]- and [8]-prismanes.