Yonemitsu-Type Reactions and Tetramolecular Condensations

SCHEME 13.76 One-pot Yonemitsu reaction/aminolysis to 3-substituted 3-indolepropionic amides 345. 

SCHEME 13.77 ProUne-catalyzed Yonemitsu reaction with subsequent nucleophilic substitution of the Meldrum s acid moiety and its proposed mechanism. 

SCHEME 13.78 Base-mediated Yonemitsu-type reaction and its proposed mechanism. 

The thermal Yonemitsu-type reaction of ethyl 2-nitroace-tate with variably substituted indoles and formaldehyde in toluene led to the formation of various tryptophan precursors in moderate to high yields [134]. Molecular sieves supported the Knoevenagel condensation step. A closely related catalyst-free version was published by Jerdme et al. in 2009 [43]. P-Ketoesters represent the CH-acidic component that undergoes a Yonemitsu-type reaction at slightly elevated temperatures to provide the desired products in moderate yields within 6-20 h. 

SCHEME 13.79 Lewis acid-catalyzed Yonemitsu-type reactions [135-137]. 

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