Silene, R2Si:C(OR)Ph (R = SiMe3 through out this abstr.), can be generated thermally from the disilacyclobutane I by [2 + 2] cycloreversion and trapped by reaction with two equiv. of phosphaalkyne, Me3CC.tplbond.P under formation of the disphosphatricyclobenzoheptane II. Low-temp. x-ray crystal structure anal. of II confirms the result. A plausible reaction mechanism, based above all on cycloaddn. steps and an ene reaction, is presented.