5 years ago

Palladium on Carbon-Catalyzed Benzylic Methoxylation for Synthesis of Mixed Acetals and Orthoesters

Palladium on Carbon-Catalyzed Benzylic Methoxylation for Synthesis of Mixed Acetals and Orthoesters
Hironao Sajiki, Yoshinari Sawama, Naoki Yasukawa, Takafumi Kanie, Marina Kuwata, Yasunari Monguchi
The palladium on carbon (Pd/C)-catalyzed direct methoxylation of the benzylic positions of linear benzyl and cyclic ether substrates proceeded in the presence of i-Pr2NEt under an oxygen atmosphere to give the corresponding mixed acetals. Cyclic acetal derivatives could also be converted into orthoesters. The present direct methoxylation via a carbon-hydrogen (C−H) functionalization can be accomplished using the easily-removed Pd/C and molecular oxygen as a green oxidant. The obtained mixed acetals were transformed into the corresponding ether products by chemoselective substitution of the methoxy group using a silyltriflate, 2,4,6-collidine, and a nucleophile. The orthoester derivative could also be transformed into the cyclic ketal under similar reaction conditions. The direct synthesis of mixed acetals and orthoesters from the corresponding benzylic ethers has been accomplished using a palladium on carbon (Pd/C) catalyst in MeOH under an oxygen atmosphere in the presence of i-Pr2NEt. The present catalytic method using molecular oxygen as a clean oxidant and easily-recovered Pd/C is valuable from the viewpoint of green sustainable chemistry.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201702278

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