The reaction of chlorodimethylorganosilanes [Cl-Si(CH3)2R; R = CH3. -CH=CH2, -CH2Cl, -CH2-CH=CH2. C6H5) with magnesiumbutadiene at 0°C in toluene gives trans-1,4-bis[dimethylorganylsilyl]-2-butenes in 55-88% yield. The amount of (Z)-isomer ranges from 0 to 17% depending on the organic substituent; no 1.2-disylilated products were detected.