AN ACTIVATED GERMANIUM METAL-PROMOTED, HIGHLY DIASTEREOSELECTIVE REFORMATSKY REACTION

Activated germanium metal, prepared by the reduction of germanium(II) iodide with potassium metal, was found to promote the Reformatsky reac tion effectively under mild conditions. In the presence of activated g ermanium metal, the reactions of alpha-bromo ketones 2a and 2b and alp ha-bromo imides 2e and 2f with benzaldehyde (1a) proceeded smoothly to give the corresponding beta-hydroxy carbonyl compounds 3a, 3d, 3e and 3f, respectively, in good yields and with good syn diastereoselectivi ty. The activated germanium metal-promoted, asymmetric Reformatsky rea ction of enantiomerically pure-oxazolidinone derivatives 2g-j with var ious aldehydes 1a-d was also examined; the highest diastereoselectivit y was achieved when (1S,2R)-2-amino-1,2-diphenylethanol-derived 2j was used as the Reformatsky donor. The excellent diastereoselectivity cou ld be explained in terms of the formation of a chairlike, six-membered transition state between the aldehyde and enolate as in the Zimmerman -Traxler model. A single recrystallization of the Reformatsky adducts, followed by hydrolysis and subsequent esterification, led to enantiom erically pure methyl 3-hydroxy-2-methylalkanoates 10j-m, with almost q uantitative recovery of the enantiomerically pure 2-oxazolidinone 14.