Bis(1-adamantyl)phosphanylsilylene 1 was reacted with ArCCR (Ar = Ph, 4-iPr-C6H4, 3-F-C6H4; R = H, Ph) at 80 °C under microwave irradiation to afford fluorescence-active SiP-heterocycles 3a-d, which may undergo unique isomerizations starting from silirene intermediates. Moreover, the treatment of 1 with AdCP furnished a heavy congener of cyclopentadiene (4), whose formation involves cleavage of the Si(II)-P bond that is rarely observed in silylene chemistry.