A highly chemo- and regioselective partially intramolecular rhodium(I)-catalyzed [2+2+2] cycloaddition of allenynes with alkynes is described. A range of diverse polysubstituted benzene derivatives could be synthesized in good to excellent yields, in which the allenynes served as synthetic equivalent to the diynes. A high regioselectivity could be observed when allenynes were treated with unsymmetrical alkynes.

The treatment of benzylallene-substituted internal alkynes with [RhCl(CO)₂]₂ effects a novel cycloisomerization by C(sp²)−H bond activation to produce hexahydrophenanthrene derivatives. The reaction likely proceeds through consecutive formation of a rhodabicyclo[4.3.0] intermediate, σ-bond metathesis between the C(sp²)−H bond on the benzene ring and the C(sp²)−Rh^III bond, and isomerization between three σ-, π-, and σ-allylrhodium(III) species, which was proposed based on experiments with deuterated substrates.

The treatment of benzylallene-substituted internal alkynes with [RhCl(CO)₂]₂ effects a novel cycloisomerization by C(sp²)−H bond activation to produce hexahydrophenanthrene derivatives. The reaction likely proceeds through consecutive formation of a rhodabicyclo[4.3.0] intermediate, σ-bond metathesis between the C(sp²)−H bond on the benzene ring and the C(sp²)−Rh^III bond, and isomerization between three σ-, π-, and σ-allylrhodium(III) species, which was proposed based on experiments with deuterated substrates.

The thermal intermolecular [4+2] cycloadditions of vicinal bis(exo-methylene)cyclooctene with carbon dienophiles efficiently produce the bicyclo[6.4.0] framework. Similar cycloadditions with the one-carbon-homologated cyclononene derivatives result in the formation of the bicyclo[7.4.0] skeleton. Both aza- and oxadieonphiles are suitable for this [4+2] reaction and provide the corresponding hetero-Diels–Alder-type products.

The Rh^I-catalyzed intramolecular [5+2–2]-type cycloisomerization of allene–allenylcyclopropanes was developed. In this reaction, ethylene was liberated from the cyclopropane ring to afford the 1,5,6,7-tetrahydroazulene skeletons.

Treatment of the allene-ene-yne substrates with [{RhCl(CO)₂}₂] effected the intramolecular [2+2+2]-type ring-closing reaction to produce various of tri- and tetracyclic derivatives containing a cyclopropane ring. The reaction is highly stereoselective as well as stereospecific with good to excellent yields.

Treatment of the allene-ene-yne substrates with [{RhCl(CO)₂}₂] effected the intramolecular [2+2+2]-type ring-closing reaction to produce various of tri- and tetracyclic derivatives containing a cyclopropane ring. The reaction is highly stereoselective as well as stereospecific with good to excellent yields.

The efficient Rh^I-catalyzed cycloisomerization of benzylallene-alkynes produced the tricyclo[9.4.0.0^3,8]pentadecapentaene skeleton through a CH bond activation in good yields. A plausible reaction mechanism proceeds via oxidative addition of the acetylenic CH bond to Rh^I, an ene-type cyclization to the vinylidenecarbene–Rh^I intermediate, and an electrophilic aromatic substitution with the vinylidenecarbene species. It was proposed based on deuteration and competition experiments.

The efficient Rh^I-catalyzed cycloisomerization of benzylallene-alkynes produced the tricyclo[9.4.0.0^3,8]pentadecapentaene skeleton through a CH bond activation in good yields. A plausible reaction mechanism proceeds via oxidative addition of the acetylenic CH bond to Rh^I, an ene-type cyclization to the vinylidenecarbene–Rh^I intermediate, and an electrophilic aromatic substitution with the vinylidenecarbene species. It was proposed based on deuteration and competition experiments.

The total syntheses of four fawcettimine-related Lycopodium alkaloids, (±)-fawcettimine, (±)-fawcettidine, (±)-lycoposerramine-Q, and (±)-lycoflexine, were completed in a highly stereoselective manner. The Pauson–Khand reaction of 4-methylidene-6-siloxyoct-1-en-7-yne followed by regio- and stereoselective hydrogenation led to the short-step preparation of the bicyclo[4.3.0]nonenone intermediate bearing a methyl group with the required stereochemistry. The subsequent chemical manipulation of the bicyclic compound afforded the 6-5-9-membered tricyclic dioxo compound, which was then transformed into the four targeted alkaloids in an alternative and more efficient fashion.