A general method for the synthesis of E and/or Z oligoisoprenoids based onPd-catalyzed homoallyl-alkenyl and homopropargyl-alkenyl cross coupling and Zr-catalyzed carboalumination

A truly general, versatile, and highly regioselective and stereoselective m ethodology for the synthesis of terpenoids containing 1,5-diene units of E and/or Z geometry critically involves (a) Pd-catalyzed homoallyl-alkenyl an d homopropargyl-alkenyl coupling and (b) Zr catalyzed carboalumination of a lkynes. In each introduction of an E or Z trisubstituted C-5 alkene unit, t he yield is excellent, and the regioselectivity and stereoselectivity level is >98%. As such, this appears to represent the first general synthetic me thod accommodating Z alkene units in > 95% regioselectivity and stenoselect ivity. Its application to some representative terpenoids of both natural an d unnatural geometries is discussed. (C) 2000 Elsevier Science Ltd All righ ts reserved.