Science of Synthesis

Guram, A. S.; Milne, J. E.; Tedrow, J. S.; Walker, S. D., Science of Synthesis: Cross Coupling and Heck-Type Reactions, (2013) 1, 94.

Although aryl- and hetarylphosphonium salts are efficient cross-coupling partners with arylboronic acids, aryl phosphates have proven more challenging. Simple aryl diethyl phosphates can succumb to Suzuki–Miyaura reaction under nickel-catalyzed conditions.[‌150‌] As with other unactivated aryl electrophiles such as pivalates and sulfamates, dichlorobis(tricyclohexylphosphine)nickel(II) and potassium phosphate afford the highest yields of the diaryl products ‌116‌ (‌Table 41‌). Electron-deficient and electron-rich aryl phosphates undergo cross coupling with similar efficiency. Free aniline groups as well as 2-substitution are tolerated as part of the electrophile structure. Cyano groups are not tolerated, presumably due to competitive cross coupling with the nitrile functional group. Electron-rich boronic acids are generally preferred; however, with activated phosphates such as 2-naphthyl, electron-poor boronic acids undergo coupling in high yields.

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