A new access to multifunctional linear triquinanes and their homologues via alpha,beta-unsaturated Fischer carbene complexes

Twelve differently substituted tricyclic hydroxy ketones 7, 8 with [5-5-x] (x = 5, 6, 7) combinations of ring sizes were prepared in a single step in 43-91% yields (10 examples with 74-91%) from the corresponding protected (2'-oxocycloalkyl)methyl-substituted cyclopentadienes 6, which were obtained by cocyclization of the alkynes 5 with the beta-dimethylamino -substituted alpha,beta-unsaturated Fischer carbene complexes 4 in 38-81% yield (6 examples with 66-81%). In most cases, the cis, anti, cis-isomers anti-7 were the major products. While the twofold cis-fusion is favored by minimal ring strain, hydrogen bonding between the hydroxy and the carbonyl group probably favors the anti-configuration of the tricyclic skeletons. Acid-catalyzed dehydration of the hydroxy ketones anti-7aa, anti-7ba, anti-7ca afforded the corresponding tricyclic dienes 15aa/16aa, 15ba, and 15ca/16ca, respectively. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).