Synthesis of spheroidal C₂₀-polyquinanes in a route towards dodecahedrane

Abstract

An approach to the hydrocarbon dodecahedrane 1 has been formulated based on a retrosynthetic theme. The starting exo,exo-tetraquinane diester 9 was conveniently synthesized from the readily available C_2v,-tetraquinane dione 5. Bis-cyclopentannulation of compound 9 employing the dichloroketene addition-ring-expansion methodology of Greene furnished the hexaquinane diester 12. The newly appended cyclopentanone rings in compound 12 were inverted via a three-step sequence involving dehydrogenation to bisenone 13, acetalisation to give compound 17, and catalytic hydrogenation to compound 18. Attempts to epimerise the exo,exo-diester functionality within the spheroidal cavity in the all-cis-hexaquinane dione diester 18 for the pivotal molecular stitching step have so far proved unsuccessful. Cyclopentannulation reactions on Hedaya-Paquette ester 23 employing Greene methodology and the Pauson-Khand reaction have been carried out. Several interesting cyclisations and transannular reactions in the resulting polyquinanes have been observed.