Darstellung, absolute Konfiguration und optische Reinheit von 2,2′-Spiro-biindan-1,1′-dion

Abstract

The absolute configuration of 2.2′-spirobiindane-1.1′-dione (2) was established as (+)-(2S) by correlation with a centrochiral key intermediate, namely by cyclization of (+)-(2R)-2-benzyl-2-methoxycarbonyl-1-indanone (9) withPPA.9 was obtained by oxidation of either methyl (+)-cis- ortrans-1-hydroxy-2-benzyl-indane-2-carboxylate (8 a, 8 b), whose absolute configurations were determined as (+)-(1S, 2R) and (1R, 2R), resp., byHoreau's method and whose optical purities by the NMR-method employing the esters with α-methoxy-α-trifluoromethylphenyl-acetic acid. The active methyl esters8 were prepared starting from the corresponding racemic ethyl ketocarboxylate4, which on reduction afforded the stereoisomeric ethylcis- andtrans-1-hydroxyindane-2-benzyl-2-carboxylates (5 a, 5 b); their relative configurations were determined by NMR. The corresponding acids7 were resolvedvia the cinchonidine salts and obtained in high optical purity (100% fortrans, 80% forcis).

Levorotatory2 was also prepared by resolution of the bis-aminoxyacetic acid derivative (via its bis-cinchonidine salt) and subsequent cleavage. [a] ^max_D of2 was determined as ±240° (benzene) by means of a chiral shift reagent. The racemization of2 withPPA under the conditions of the asymmetric synthesis was studied.