Multiple Horner-Emmons cyclizations as a Route to Nonbenzenoid Aromatics. Synthesis of Polycyclic Dodecalenes

Quadruple Horner-Emmons cyclization reaction between the tetraaldehyde 6 and the bis phosphonate 7 afforded (9E, l4E, 24E, 29E)-hexabenzo[d, f, jk, o, q, uv]dodecalene (1a) and its 9E, 14Z, 24Z, 29E isomer (1b) in 4.2 and 0.4% yield, respectively. The analogous reaction between the tetrakis phosphonate 8 and the dialdehyde 4 afforded la in 0.3% yield. The double Horner-Emmons reaction between 4 and 7 afforded (9E, 19E)-tetrabenzo[a, c. g, i]cyclododecene (2a) in 8.0% yield. The advantages of the multiple Horner-Emmons reaction in the synthesis of polycyclic nonbenzenoid aromatics as compared with the conventional multiple Wittig reaction are discussed.