The combination of chiral preparative HPLC separation, VCD measurements and theoretical calculations allows the unambiguous determination of the absolute configuration of the conformationally flexible products of copper-catalyzed carbene insertion reactions. DFT calculations were used to predict the stereochemical outcome of the copper-bis(oxazoline)-catalyzed C-H insertion reaction between methyl diazophenylacetate and tetrahydrofuran, and also the absolute configuration of the major stereoisomers derived from the same reaction with different cyclic ethers. These predictions were verified experimentally through NMR and VCD spectroscopy and allowed rationalizing the stereochemical outcome of these reactions without further derivatization of the products, which can be problematic under certain conditions as described in this manuscript.