The synthesis of a bicyclo[6.3.0]undecene skeleton characteristic of a number of cyclooctanoid natural products is described. The methodology applied relies on an intramolecular reductive coupling of a dialdehyde promoted by low valent titanium to construct the key eight-membered ring. The use of C8K-TiCl3 as an alternative process to the classical coupling developed by McMurry is presented. The dialdehyde 15, precursor of the bicyclo[6.3.0]undecene system, was constructed in a concise manner from 2-carbomethoxy-cyclopentanone in 5 steps with an overall yield of 40%. The key carbonyl coupling of dialdehyde 15 to produce the eight-membered ring proceeded in low yields (~10%) despite several attempts to increase its efficiency.
cyclooctanoids; carbonyl coupling; low-valent titanium
