Novel and stereoselective methods for the preparation of aromatic lactams via reductive coupling reactions mediated by SmI2

Samarium(II) diiodide-mediated reductive cross-coupling of N-alkylated phth alimides with carbonyl compounds is shown to afford hydroxylated alpha-hydr oxylactams, Ketoamides obtained by dehydration of these compounds through k eto-enol tautomer isomerization were reduced with NaBH4 in a completely ste reoselective manner in the presence of CeCl3 to give three-aromatic lactams as the sole product. Direct reductive deoxygenation of these alpha-hydroxy lactam intermediates with Et3SiH in the presence of Lewis acid also display ed high stereoselectivity to afford the same threo-lactams exclusively. The mechanistic origins of this stereoselectivity are briefly documented. (C) 2000 Elsevier Science Ltd. All rights reserved.