Compounds of structure (I): including stereoisomers, tautomers and salts thereof, wherein R1, R2, R3, R4, R5, R6, X, Y and Z are as defined herein. Such compounds are useful for the preparation of diarylpropane compounds. Methods for the preparation of compounds of structure (I) are also disclosed, as are methods employing compounds of structure (I) for the preparation of diarylpropanes.