Catalysis of ring expansion of 1-methylcyclopropylmethanol to 1-methylcyclobutanol by rhodium(I)

Abstract

Stoichiometric reaction between [Rh2(μ-Cl)2(CO)4] and CH2CH2CHCMe2OPNB, OPNB = 4-nitrobenzoate, gave [Rh2(μ-OPNB)2(CO)4] and Me2C=CHCH2CH2Cl. The complex [Rh2(μ-Cl)2(CO)4] in acetone solution catalyzes the ring expansion of CH2CH2CMeCH2OH to give CH2CH2CH2CMeOH, and experiments with labelled derivatives indicate that the rhodium complex acts as a Lewis acid. The reaction is zero order in cyclopropyl derivative but second order in catalyst concentration. The equilibrium constant for the reaction is 21 at 40 °C and a mechanism is proposed.