Grignardreactions on methyl 4-methyl, 5-oxo, 5-phenyl (pX substituted) pentanoates 1-6 (X = H, Me, F, Cl, Br, OMe) produced mixtures of cis-(7-11) and trans-(12-16) tetrahydro 5,6 dimethyl-6-phenyl -2H-pyran-2-ones. They were isolated by HPLC and characterized by 1H and 13C techniques. The stereochemistry of Grignardreactions in THF with CH3MgCl was determined at 0° and 60°.