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

Abstract We report two new asymmetric syntheses of o -carboranylalanine, [3-(1,2-dicarba- closo -dodecaborane(12)-1-yl)-2-aminopropanoic acid] ( 1 ), using the Fitzi–Seebach imidazolidinone and the Oppolzer–Lienard sultam procedure, respectively. Both methods gave high diastereoselectivity but some racemisation of 1 (EP, 91–96%) was observed after the final hydrolysis step in the imidazolidine procedure. The Oppolzer procedure gave 1 with EP>99%. The absolute configuration of the (−)- 1 (CH 3 OH) was established as S . The preparation of ( S )-Boc- 1 is reported. Attention is drawn to a spontaneous self-degradation of the zwitterionic form of 1 in water and methanol solutions.