Abstract
Recently, we developed a palladium-catalyzed cycloalkenylation (Scheme 1, eq 1), and this protocol has been successfully adapted to the stereoselective syntheses of polycyclic natural products. In our efforts to expand the utility of this palladium-catalyzed cycloalkenylation, we undertook a concise synthesis of 6-oxatricyclo[6.3.0.0^<1'5>]undecane. Although ketene silyl acetal 3 gave rise to desired tricyclic compound 4 under palladium-catalyzed cycloalkenylation conditions, the yield was less than 9% probably due to the instability of ketene silyl acetal 3 (Scheme 1, eq 2). To solve this problem, we recently developed a palladium-catalyzed oxidative cyclization of olefinic keto and lactone esters (2^<nd> generation palladium-catalyzed cycloalkenylation) as an alternative method of the original palladium-catalyzed cycloalkenylation for the construction of polycyclic compounds (Scheme 1, eq 3). In this presentation, we will describe the total synthesis of iridolactones and alkaloids shown in schemes 2-4, employing the 2nd generation palladium-catalyzed cycloalkenylation.
