Collect. Czech. Chem. Commun. 1997, 62, 1585-1598

Synthesis, Conformational Analysis and Transannular Reactions of 5,9-Propanobenzo[7]annulene Derivatives

Pelayo Camps, Diana Görbig, Victoria Muñoz-Torrero and Francesc Pérez

Unitat de Química Farmàceutica, Facultat de Farmàcia, Universitat de Barcelona, Av Diagonal s/n, E-08028 Barcelona, Spain


(5α,9α,11β)-11-Hydroxy-6,7,8,9-tetrahydro-5H-5,9-propanobenzo[7]annulen-7-one ethylene ketal (6a) and its 11α-methyl derivative (6b) were prepared from monoketal 3. These compounds underwent acid-catalyzed transannular reactions leading to 6,7,8,9-tetrahydro-5H-5,9-propanobenzo[7]annulene derivatives 5a, 8a and 5b, 8b, respectively, depending on the reaction conditions. The compounds 6a and 6b were dehydrated to 6,7,8,9-tetrahydro-5H-5,9-prop[1]enobenzo[7]annulen-7-one (9a) and its 11-methyl derivative (9b), respectively. The conformational analysis of the 5,9-propanobenzo[7]annulene derivatives by molecular mechanics calculations (MM3 program) and the 1H NMR data show that hydroxyketal 6a and the related compound (5α,7β,9α)-6,7,8,9-tetrahydro-5H-5,9-propanobenzo[7]annulen-7-ol (4) exist mainly in the boat-chair conformation with the boat cycloheptenol ring, while for hydroxyketal 6b the chair-boat conformation (chair cycloheptenol ring) seems to be the preferred one.

Keywords: Annulenes; Transannular reactions; Conformational analysis; 5,9-Propanobenzo[7]annulene derivatives.