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  • Experimental mechanistic studies of the tail-to-tail dimerization of methyl methacrylate catalyzed by N-heterocyclic carbene.

Experimental mechanistic studies of the tail-to-tail dimerization of methyl methacrylate catalyzed by N-heterocyclic carbene.

The Journal of organic chemistry (2013-08-15)
Terumasa Kato, Yoshiya Ota, Shin-ichi Matsuoka, Koji Takagi, Masato Suzuki
ABSTRACT

We and others have previously reported the intermolecular umpolung reactions of Michael acceptors catalyzed by an N-heterocyclic carbene (NHC). The representative tail-to-tail dimerization of methyl methacrylate (MMA) has now been intensively investigated, leading to the following conclusions: (1) The catalysis involves the deoxy-Breslow intermediate, which is quite stable and remains active after the catalysis. (2) Addition of the intermediate to MMA and the final catalyst elimination are the rate-limiting steps. Addition of the NHC to MMA and the proton transfers are relatively very rapid. (3) The two alkenyl protons of the first MMA undergo an intermolecular transfer to C3 and C5 of the dimer. (4) The initial proton transfer is intermolecular. (5) Compared with the benzoin condensation, noticeable differences in the kinetics, reversibility, and stability of the intermediates are observed.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Methyl methacrylate, 99%, stabilized
Pricing and availability is not currently available.
Sigma-Aldrich
Methyl methacrylate, contains ≤30 ppm MEHQ as inhibitor, 99%
Pricing and availability is not currently available.
Supelco
Methyl methacrylate solution, certified reference material, 1000 μg/mL in methanol
Pricing and availability is not currently available.