Samarium diiodide is an efficient precatalyst for tandem Michael-aldol reac
tions, which allow the formation of two carbon-carbon bonds by successive a
dditions of a ketene silyl acetal and an aldehyde on cyclic alpha,beta -uns
aturated ketones. The adducts are isolated as silyl ethers, in good yields,
and in some cases with high diastereoselectivities when the reactions are
performed at low temperatures. Comparative study of the activities of other
lanthanide iodides for the same tandem reactions is presented. A key step
for a formal synthesis of PGF(2 alpha) has been performed by a tandem Micha
el-aldol samarium-catalysed sequence. (C) 2001 Elsevier Science Ltd. All ri
ghts reserved.