Homo- Versus Hetero- [2+2+2] Rhodium-Catalyzed Cycloaddition: Effect of a Self-Assembled Capsule on the Catalytic Outcome.

The cationic chloro-P-{[4-(diphenylphosphanyl)phenyl]-N,N-dimethylmethanammonio(norbornadiene)rhodium(I) complex was encapsulated inside a self-assembled hexameric capsule. This capsule was obtained through a reaction involving 2,8,14,20-tetra-undecyl-resorcin[4]arene and water in chloroform. The formation of an inclusion complex was deduced from a combination of spectral measurements (UV-visible spectroscopy, 1H, 31P{1H} NMR and DOSY). The rhodium complex was evaluated in the [2+2+2] cycloaddition between N,N-dipropargyl-p-toluenesulfonamide and arylacetylene derivatives. In the presence of two equivalents of arylacetylenes in water-saturated chloroform at 60 °C for 24 h, the 4-methyl-N-(prop-2-yn-1-yl)-N-((2-tosylisoindolin-5-yl)methyl)benzenesulfonamide, the homocycloaddition product of 1,6-diyne is predominantly formed. In the presence of the supramolecular capsule, a selectivity inversion in favor of 5-aryl-2-tosylisoindoline is observed, with heterocycloaddition products formed in proportions between 53 and 69%.