Determination of the absolute configuration of inherently chiral resore[4]arenes

Klaes M, Neumann B, Stammler H-G, Mattay J. Determination of the absolute configuration of inherently chiral resore[4]arenes. European Journal of Organic Chemistry. 2005;2005(5):864-868.The absolute configuration of twelve inherently chiral resorcarenes was determined using a combination of the X-ray structure of (-)-3a and optical rotation as well as NMR techniques. Starting from a racemic mixture of 1 both diastereomers (-)-3a and (+)-3b can be obtained in high yields in two steps and the absolute configuration of these diastereomers could be determined by X-ray analysis. Using enantiomerically pure (-)-1 for the same reactions, however, (+)-3b is formed. The alkylation of (-)-1 with (S)-2-methylbutyl tosylate and the methylation of (-)-5a lead to the same resorcarene (-)-4a, while the alkylation of (+)-1 and the methylation of (+)-5b yield in resorcarene (+)-4b. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)