Asymmetric Halogenation and Hydrohalogenation of trans-2-Butenoic Acid in a Crystalline α-Cyclodextrin Complex

Article abstract of DOI:10.1021/jo00289a032

trans-2-Butenoic acid was asymmetrically hydrohalogenated and halogenated in a crystalline α-cyclodextrin complex.Exposure to gaseous hydrogen bromide at 20 deg C and to hydrogen chloride at 0 deg C gave (S)-(+)-3-bromobutanoic acid in 58percent and (S)-(-)-3-chlorobutanoic acid in 64percent enantiomeric excesses, respectively.At 45-50 deg C, the guest in the cavity of the cyclodextrin reacted with gaseous bromine or chlorine to produce erythro-dihalides with extremely low optical activities; no products were obtained on treatment with bromine for 50 h at the lower temperatureof 20 deg C.The crystal structure of the complex was determined to be: C36H60O30*C4H6O2*5H2O; FW = 1149.0; orthorhombic; space group, P2₁2₁2₁; Z = 4; a = 14.406 (5), b = 38.174 (12), and c = 9.430 (3) Angstroem; V = 5185.9 Angstroem³; D_x = 1.472, D_m = 1.475 g/cm².A mechanism for the observed chiral induction in the present gas-solid reaction is discussed in terms of the crystal structure of the complex.