Zirconocene-catalyzed carbomagnesation reactions of cyclic ethers 4 and 7 with n-PrMgCl and n-BuMgCl afford homoallylic and bishomoallylic alcohols 5, 8, 9, and 11 in similar to 40% yield and exceptional levels of enantioselectivity and regiocontrol. Where n-BuMgCl is used as the alkylating agent, high levels of diastereochemical control are also observed (cf. 9 vs 10 in entries 4 and 5 of Table 1). Studies reported herein underline a number of important mechanistic issues : (i) Although zirconocene-alkene complexes 3 exist as a mixture of diastereomers in solution (syn and anti), it is only one of the isomers which reacts to afford the observed products. (ii) Whereas insertion of an alkene substrate into the unsymmetric complexes 3 and 18 proceeds with low levels of regioselectivity at 22 degrees C, at 70 degrees C high levels of regiocontrol are observed (cf. intermediacy of 20 vs 24 in Scheme 4). In this context, various mechanistic experiments shed light on factors that may be responsible for the observed temperature effect. (iii) Unusual modes of preference for the regioselectivity in beta-hydride abstraction of intermediate dialkylzirconocene are reported; these observations may be accounted for through consideration of the steric effects imposed by the cyclohexyl groups of the chiral ligand and the stereoelectronic requirements of the elimination reaction.