It has been established that ac ationic rhodium(I)/ binap complex catalyzest he cross-cyclotrimerization of two molecules of am onosubstituted allene with one molecule of af unctionalized alkyne to give 3,6-dialkylidenecyclohex-1-enes.I nc ontrast, the reactions involving di-or trisubstituted allenes and/or unfunctionalized alkynes afforded cross-dimerization products,substituted dendralenes,through b-hydrogen elimination from the corresponding rhodacycles.Transition-metal-catalyzed intermolecular cross-cyclotrimerization and cross-dimerization reactions of alkynes with alkenes are efficient and atom-economical methods for the synthesis of substituted six-membered carbocycles and dienes, respectively.[1] In contrast, similar transformations using allenes in place of alkenes have been reported in al imited number of examples.[2] As examples of the cross-cyclotrimerization of alkynes with allenes, [3][4][5] the nickel-catalyzed reactions of one molecule of am onosubstituted allene with two molecules of an electron-deficient internal alkyne followed by aromatization through olefin isomerization, which affords the corresponding pentasubstituted benzenes, has been reported (Scheme 1a).[3a] However,t he usable alkynes are limited to electron-deficient alkynoates,a nd electron-rich alkynes cannot be employed.[3a] Furthermore, as elective and general method for the cross-cyclotrimerization of two molecules of an allene and one molecule of an alkyne has not been reported to date. [5] As examples of the cross-dimerization of allenes with alkynes,t hermal reactions giving substituted dendralenes have been reported (Scheme 1b). [6][7][8] However,t he usable alkynes are limited to electron-deficient dimethyl acetylenedicarboxylate and (trifluoromethyl)acetylene.[6] Herein, we disclose the crosscyclotrimerization of two molecules of am onosubstituted allene with functionalized alkynes,a nd cross-dimerization of di-or trisubstituted allenes with both functionalized and unfunctionalized alkynes.Recently,o ur research group reported the rhodiumcatalyzed enantioselective [2+ +2+ +2] cycloaddition of tosylamide-linked 5-allenals and 5-allenones with internal alkynes. [9] In this study,w ef ound that the reaction of the tosylamide-linked 5-allenone with di-tert-butylacetylenedicarboxylate in the presence of ac ationic rhodium(I)/binap catalyst does not afford the expected [2+ +2+ +2] cycloaddition product, but instead delivers an unexpected cross-cyclotrimerization product, 3,6-dialkylidenecyclohex-1-ene derivative, in good yield (Scheme 2).Thus,w ee xamined the reaction of the monosubstituted allene 1a with di-tert-butylacetylenedicarboxylate (2a)inthe presence of the same rhodium catalyst (Table 1). Pleasingly, the cross-cyclotrimerization proceeded at room temperature to give the corresponding 3,6-dialkylidenecyclohex-1-ene 3aa,a lthough the regioisomer 4aa was generated as aminor product (entry 1). Theeffect of biaryl bis(phosphine) ligands was then examined (entries 1-5). Increasing the dihedral angle of ligands impro...