Evaluation of TlOH Effect for Pd⁰-Mediated Cross-Coupling of Methyl Iodide and Excess Boronic Acid Ester toward Fabrication of [¹¹C]CH₃-Incorporated PET Tracer

Hiroko Koyama, Hisashi Doi, Masaaki Suzuki

Department of Clinical and Experimental Neuroimaging, Center for Development of Advanced Medicine for Dementia, National Center for Geriatrics and Gerontology, Obu-shi, Japan.
Division of Bio-function Dynamics Imaging, Riken Center for Life Science Technologies (CLST), 6-7-3 Minatojima Minamimachi, Kobe, Japan.
Division of Regeneration and Advanced Medical Science, Gifu University Graduated School of Medicine, Gifu University, Gifu, Japan.

DOI: 10.4236/ijoc.2013.33030                

Abstract

The use of thallium(I) hydroxide (TlOH) as a base is known to extremely accelerate the Suzuki-Miyaura cross-coupling reaction using organoboronic acid or organoboronic acid ester as a substrate. Here, we investigated the effects of TlOH by comparing with other conventional bases such as KOH, K₂CO₃, and CsF for Pd⁰-mediated rapid cross-coupling reactions between CH₃I and organoborane reagents, such as phenyl-, (Z)-4-benzyloxy-2-butenyl-, and benzylboronic acid pinacol esters under the conditions CH₃I/borane/Pd⁰/base (1:40:1:3) in THF/H₂O or DMF/H₂O for 5 min with an aim to fabricate a PET tracer efficiently. Consequently, however, the use of TlOH was much less efficient than the other bases for the acceleration of cross-coupling reactions. Thus, it was reconfirmed that the milder and non-toxic conditions using K₂CO₃ or CsF so far developed by our group were most appropriate for the rapid C-methylations.

Keywords

Synthesis of Short-Lived Positron Emission Tomography Probes; Suzuki-Miyaura-Type Rapid Cross-Coupling; Rapid C-Methylation; TlOH

Conflicts of Interest

The authors declare no conflicts of interest.

References

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