Enantioselective synthesis and absolute configurations of the enantiomers of o-carboranylalanine

We report two new asymmetric syntheses of o-carboranylalanine, [3-(1,2-dica rba-closo-dodecaborane(12)-1-yl)-2-aminopropanoic acid] (1), using the Fitz i-Seebach imidazolidinone and the Oppolzer-Lienard sultam procedure, respec tively. Both methods gave high diastereoselectivity but some racemisation o f 1 (EP, 91-96%) was observed after the final hydrolysis step in the imidaz olidine procedure. The Oppolzer procedure gave 1 with EP>99%. The absolute configuration of the (-)-1 (CH3OH) was established as S. The preparation of (S)-Boc-1 is reported. Attention is drawn to a spontaneous self-degradatio n of the zwitterionic form of 1 in water and methanol solutions. (C) 2000 E lsevier Science Ltd. All rights reserved.