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14.4.10.1.1.4.1.2 Method 2: Base-Catalyzed Cyclization of N,N-Dialkyl-2-phenoxybenzamides

DOI: 10.1055/sos-SD-014-00294

Williams, A. C.; Camp, N.Science of Synthesis, (200314602.

The directed ortho-metalation strategy developed by Snieckus,[‌1039‌] has been successfully applied in the synthesis of 9H-xanthen-9-ones.[‌1040‌] The reaction uses a diphenyl ether containing a 2-diethylamide substituent that acts as a metalation directing group. Treatment of the amide with lithium diisopropylamide gives an anion regiospecifically, ortho to the bridging oxygen that undergoes an intramolecular ring-closing reaction to form the 9H-xanthen-9-ones 684 in good to excellent yield (Scheme 266). These reactions are carried out under mild conditions and tolerate a variety of substituents. In fact, certain substituents such as methoxy and chloro groups act as secondary metalation directing groups and control the regiospecificity of the anion formation and ultimately the structure of the cyclization product.

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