Treatment of the tetrametallic carbido-benzofuryl cluster (C5Me5)WOs3(mu(4)-C)(mu-H)(2)(mu-C8H6O)(CO)(9) (1) with pressurized CO gas affords a carbido cluster (C5Me5)WOs3(mu(4)-C)(mu-H)(CO)(11) (2) in nearly quantitative yield. The reactions of 2 with diisopropyl acetylenedicarboxylate (DPAD) are investigated. If complex 2 is first treated with Me3NO, the incorporation of DPAD at room temperature affords a cluster compound (C5Me5)WOs3(CO)(10)[C3H(CO2Pri)(2)] (3) in moderate yield, in which the allyl group is formed by hydride migration to the carbide. Complex 3 undergoes a facile metathesis to yield an isomer (4) with a different arrangement of the allyl C-3 backbone. Upon thermolysis, complex 4 converts to a eta(6)-tetramethylfulvene complex [C5Me4(CH2)]WOs3(mu-H)[C3H(CO2Pri)(2)](CO)(9) (5) by activation of a ring-methyl in the C5Me5 ligand and a trialkylidyne cluster (C5Me5)WOs3(mu(3)-CH)(mu(3)-CCO2Pri)(2)(CO)(9) (6) by cleavage of two allyl C-C bonds. The possible mechanism of their interconversion is discussed. If the reaction of the Me3NO-activated complex 2 and DPAD is carried out in refluxing toluene, we obtained one more compound (C5Me5)WOs3[CC2(CO2Pri)(2)H](CO)(10) (7) in low yield, which appears to farm through a secondary process involving hydride migration to the DPAD molecule instead.