Nucleophilic displacement chemoselectivity

Convertible isocyanide reagent 66 allows a mild and chemoselective in situ post-Ugi activation of the isonitrile bom amide with simultaneous deprotection of the nucleophilic amine, that is, liberation and activation of two Ugi-reactive groups, if desired also under subsequent lactam formation [33]. Another recently introduced convertible isocyanide, l-isocyano-2-(2,2-dimethoxyethyl)-benzene 73, was shown effective by Rhoden et al. In the course of this short sequence, a hydrolytically labile W-acylindole 78 is formed, which is displaced intramolecularly by the amine portion of the former Boc-protected amino acid 75 (Scheme 13). 

Displacement of the C7-F of 106 (Scheme 4.20) proceeded via chemoselective attack by the more nucleophilic pyrrolidine nitrogen rather than the piperidine nitrogen to afford the intermediate C7-octahydropyrrolopyridine. Hydrolysis of the ethyl ester with hydrochloric acid ultimately furnished moxifloxacin (2). 

KHMDS was shown to be as effective as LHMDS in the boron-assisted displacement of secondary chloride which led to the corresponding protected amine with inversion of configuration (eq 26). The chemoselective displacement of the chloride is greatly facilitated by the a-boro substituent, which is known to cause a rate acceleration on the attack of nucleophiles of approximately two orders of magnitude relative to the primary halide. ... 

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