Preparation of beta(2)-amino acid derivatives (beta(2)hThr,beta(2)hTrp,beta(2)hMet, beta(2)hPro, beta(2)hLys, pyrrolidine-3-carboxylic acid) by using DIOZ as chiral auxiliary

The title compounds were prepared from valine-derived N-acylated oxazolidin-2-ones, 1-3, 7, 9, by highly diastereoselective ( >= 90%) Mannich reaction (-> 4-6; Scheme 1) or aldol addition ( -> 8 and 10; Scheme 2) of the corresponding Ti- or B-cnolates as the key step. The superiority of the '5,5-diphenyl-4-isopropyl-1,3-oxazolidin-2-one' (DIOZ) was demonstrated, once more, in these reactions and in subsequent transformations leading to various t-Bu-, Boc-, Fmoc-, and Cbz-protected beta(2)-homoamino acid derivatives 11 - 23 (Schemes 3-6). The use of omega-bromo-acyl-oxazolidinones 1-3 as starting materials turned out to open access to a variety of enantiomerically pure trifunctional and cyclic carboxylic-acid derivatives.