Metalated phenylphosphine oxides reacted with aldehydes at room temp. to give trans olefins with high selectivity. Thus, Ph2P(O)CH2Ph was treated with BuLi, then with PhCHO to give 78% trans-stilbene. The configuration of a double bond present in the starting material was conserved throughout the reaction sequence, e.g., (E)-Ph2P(O)CH:CHMe reacted with BuLi and PrCHO to give 28% (E,E)-MeCH:CHCH:CHPr, with only traces of the other isomers. [on SciFinder (R)]