It has been established that a cationic rhodium(I)/H8 -binap complex catalyzes the [3+2+2] cycloaddition of 1,6-diynes with cyclopropylideneacetamides to produce cycloheptadiene derivatives through cleavage of cyclopropane rings. In contrast, a cationic rhodium(I)/(S)-binap complex catalyzes the enantioselective [2+2+2] cycloaddition of terminal alkynes, acetylenedicarboxylates, and cyclopropylideneacetamides to produce spiro-cyclohexadiene derivatives which retain the cyclopropane rings.

It has been established that a cationic Rh(I)/(S)-Segphos or (S)-DTBM-Segphos complex and benzoic acid catalyze the enantioselective cycloisomerization of 1,6-enynes, possessing carbonyl groups at the enyne linkage, to 2-alkylidenebicyclo[3.1.0]hexanes. The present cycloisomerization may involve site selective γ-hydrogen elimination. The one-pot enantioselective cycloisomerization and lactonization of 1,6-enynes, leading to bicyclic lactones, has also been accomplished.

It has been established that an electron-deficient Cp(E) rhodium(III) complex catalyzes the oxidative [4+2] annulation of substituted arenecarboxylic and acrylic acids with alkynes under ambient conditions (at RT-40 °C, under air) without using excess amounts of substrates to produce the corresponding substituted isocoumarins and α-pyrones in high yields. Minor modification of reaction conditions depending on the coordination ability of alkynes realized the high efficiency.

It has been established that an electron-deficient (η -cyclopentadienyl)rhodium(III) [Cp Rh ] complex is capable of catalyzing the decarboxylative and oxidative [2+2+2] annulation of benzoic acids with alkynes to produce substituted naphthalenes at room temperature. The appropriate choice of the additive and the solvent is crucial for this transformation. This catalyst system allowed use of oxygen as a terminal oxidant and broadened the substrate scope including both aromatic and aliphatic alkynes. In this catalysis, the electron deficient nature of the Cp Rh catalyst would cause the strong rhodium-π interaction, which accelerates the decarboxylation as well as the C-H bond cleavage.

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Scheme 1. Transition-metal-catalyzed asymmetric [2+2+2] cycloadditions involving alkene units.

It has been established that cationic rhodium(I)/axially chiral biaryl bis(phosphine) complexes catalyze the asymmetric [2+2+2] cycloaddition of 1,6-enynes with electron-rich functionalized alkenes, enamides, and vinyl carboxylates, to produce the corresponding protected cyclohexenylamines and cyclohexenols. Interestingly, regioselectivity depends on structures of substrates. The present cycloaddition was successfully applied to the enantioselective total synthesis of (-)-porosadienone by using the amide moiety as a leaving group.

It has been established that a cationic rhodium(I)–BINAP complex catalyzes the enantioselective [2 + 2 + 2] cycloaddition of a tosylamide-linked 5-allenal and 5-allenone with internal alkynes, leading to bicyclic oxygen heterocycles.