STEREOSELECTIVE PINACOL COUPLING OF PLANAR CHIRAL (BENZALDEHYDE)CR(CO)(3), (BENZALDIMINE)CR(CO)(3), FERROCENECARBOXALDEHYDE AND (DIENAL)FE(CO)(3) COMPLEXES WITH SAMARIUM DIIODIDE

An intermolecular pinacol coupling of the planar chiral tricarbonylchr omium complexes of o-substituted benzaldehydes or benzaldimines with s amarium(II) diiodide in THF produces exclusively threo 1,2-diols or 1, 2-diamines in an optically pure form, while the corresponding racemic o-substituted benzaldehyde or benzaldimine chromium complexes give a m ixture of threo and erythro pinacol coupling products in a various rat io depending upon the nature of o-substituent. Similarly. planar chira l 2-substituted ferrocenecarboxaldehydes and (dienal)Fc(CO)(3) produce the corresponding 1,2-diols with high stereoselectivity. The generate d transition metal-complexed ketyl radical intermediates are configura tionally stable with restriction to a relation about C-alpha-C-ipso bo nd. (C) 1998 Elsevier Science Ltd. All rights reserved.