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.