A New Tandem Route to Angular Tetraquinanes. Synthesis of the Waihoensene Ring System

Abstract

[formula: see text] This paper describes a new tandem reaction sequence leading to angularly fused polyquinanes from squaric acid-derived bicyclo[6.3.0]-undecadienediones. Such compounds undergo a dual Michael addition. The enolate form in the first intermolecular addition undergoes the second intramolecular transannular addition to give the angular polyquinanes. A particularly interesting example is a catalytic transformation of cis-13-methylyricyclo[10.3.0.0]pentadeca-4(5),12(13)-diene-3 ,14-dione to (3R*,3aS*,5aR*,9aR*,11aR*)-3-methyl-1,2,3,5,5a,6 ,7,10,11,11a-decahydro-4H- pentaleno[6a,1-c]indene-2,10-dione, a compound having the tetracyclic ring system found in the natural product waihoensene. The mechanism and synthetic scope of these reactions are discussed.