Reaction of the magnesium complexes of substituted 1,3-dienes with either carboxylic esters or lactones at low temperature (-78 to -10 degrees C) generates the magnesium salt of a cyclopropanol (4). This intermediate can either be trapped as an acetate of the cyclopropanol (9) or it can be heated to yield substituted cyclopentenols. Moreover, when this intermediate is protonated, it undergoes an intramolecular rearrangement to yield beta,gamma-unsaturated ketones. Accordingly, this protocol allows the generation of a wide range of complex molecules from a single intermediate in high isolated yields.