The first reagent-controlled asymmetric halolactonizations. Dihydroquinidine-halogen complexes as chiral sources of positive halogen ion

The first reagent-controlled asymmetric halolactonizations are described. Complexes of I⁺ with O-acyl- and O-aryldihydroquinidines are used to promote the asymmetric halolactonization of prochiral Γ,δ-unsaturated carboxylic acids with low but measurable and reproducible enantioselectivity. Experimental factors affecting the ee's are described.