Synthesis, NMR Spectroscopic Characterization and Polysiloxane‐Based Immobilization of the Three Regioisomeric Monooctenylpermethyl‐β‐cyclodextrins and Their Application in Enantioselective GC

2 I−VI ,3 I−VII ,6 I−VII ‐Eicosa‐ O ‐methyl‐2 I ‐ O ‐(oct‐7‐enyl)cyclomaltoheptaose, 2 I−VII ,3 I−VI ,6 I−VII ‐eicosa‐ O ‐methyl‐3 I ‐ O ‐(oct‐7‐enyl)cyclomaltoheptaose, and 2 I−VII ,3 I−VII ,6 I−VI ‐eicosa‐ O ‐methyl‐6 I ‐ O ‐(oct‐7‐enyl)cyclomaltoheptaose were synthesized by selective introduction of an oct‐7‐enyl group at one of the O ‐2, O ‐3, or O ‐6 positions of selectively methylated cyclomaltoheptaose (β‐cyclodextrin, CD) and, depending on the synthetic route, by a subsequent permethylation step. Each of the regioisomeric mono‐oct‐7‐enylated permethylated β‐cyclodextrin derivatives was anchored by hydrosilylation to a hydridomethyldimethylsiloxane copolymer to yield unambiguously O ‐2‐, O ‐3‐, and O ‐6‐bonded chiral stationary phases (CSP) of Chirasil‐Dex, which were evaluated in enantioselective gas chromatography (GC). O ‐6‐Chirasil‐Dex displayed slightly inferior enantioselectivity relative to either O ‐3‐ or O ‐2‐Chirasil‐Dex. The statistical synthesis of the CSP by mono‐oct‐7‐enylation of β‐CD under varying reactions conditions (base, solvent), without the use of hydroxy group protection chemistry, furnished a mixture of O ‐6‐ and O ‐2‐Chirasil‐Dex in dimethylformamide and predominantly the O ‐2‐regioisomer in dimethyl sulfoxide. Chirasil‐Dex, previously formulated exclusively as the O ‐6 regioisomer, should be revised as an O ‐2‐ and O ‐6‐Chirasil‐Dex mixture. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)