Lithium diorganocuprates add across the triple bond of substituted and non-substituted acetylenic acetals and ketals to give dialkenylcuprates, which can be decomposed into alkoxyallenes or may be trapped with a variety of electrophiles, such as alkyl, alkenyl, alkynyl and aryl halides. They may also undergo conjugate addition to a-ßunsaturated esters and ketones. The method is used for the synthesis of (±)-manicone, pure geranial and (E,Z)2,4-dienals.