Regioselective Dimerization of Methylcyclopentadiene inside Cucurbit[7]uril

Area of Science:

• Supramolecular chemistry
• Organic catalysis
• Reaction mechanism

Background:

• Macrocyclic receptors can induce catalytic activity and control reaction selectivity.
• The dimerization of methylcyclopentadiene (MCPD) isomers is a model reaction for studying selectivity.
• Cucurbit[n]uril (CB7) is a rigid macrocycle known for its host-guest chemistry.

Purpose of the Study:

• To investigate the effect of CB7 on the dimerization of MCPD isomers in aqueous solution.
• To determine the regioselectivity and diastereoselectivity of the MCPD dimerization in the presence of CB7.
• To elucidate the mechanism by which CB7 influences the reaction pathway.

Main Methods:

• Dimerization of MCPD isomers in aqueous solution at pH 3.
• Use of cucurbit[7]uril (CB7) as a supramolecular catalyst.
• Analysis of reaction products using spectroscopic and chromatographic techniques.
• Quantum-chemical calculations to support mechanistic interpretations.

Main Results:

• CB7 significantly accelerates the dimerization rate of MCPD.
• A striking regioselectivity was observed, favoring the endo-3,7-dimethyl-3a,4,7,7a-tetrahydro-1H-4,7-methanoindene adduct.
• This specific adduct is a minor product in the absence of CB7.
• The selectivity arises from the formation of a heteroternary complex within CB7, dictating reactant orientation.

Conclusions:

• CB7 acts as an effective supramolecular catalyst for MCPD dimerization.
• Molecular confinement within CB7 precisely controls the regioselectivity of the reaction.
• The observed selectivity is attributed to the specific arrangement of MCPD isomers within the CB7 cavity, guided by their methyl groups.