Unusual Orthogonality in the Cleavage Process of Closely Related Chelating Protecting Groups for Carboxylic Acids by Using Different Metal Ions

Abstract

Three structurally related relay protecting groups for carboxylic acids that are based on chelating amines have been developed. These protecting groups can easily be introduced by coupling the carboxylic acid and the corresponding amine in the presence of 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU). In addition to being stable to a whole array of reaction conditions, these protecting groups are also stable under acidic and basic conditions, allowing them to be used in combination with the ester protection of carboxylic acids. The cleavage of these protecting groups is activated by the chelation of metal ions, involving an unusual coordination of the amide nitrogen. Despite their similarity, cleavage of these protecting groups is possible in both a stepwise and an orthogonal fashion by applying different metal salts.

Unusual metal complexes of N,N-bis(2-picolyl)amides – A comparative study of structure and reactivity

“…[15][16][17][18][19][20][21] In addition, the cleavage can proceed in an intramolecular fashion and give γ-, δ-and ε-lactones in moderate to high yields. [22] Figure 1: Parameters for the quantitative description of the (non-)/planarity of amides; a) twist angle τ, b) Winkler-Dunitzparameter χ N .…”

Modulation of Olefin Metathesis Reactions by Chelation

“…The obtained values with the different salts are a reflection of the stability of the chelation as already observed in earlier studies concerning methanolysis of chelating amides with different metal salts. [8][9][10] These data also revealed that the bpa unit forms more-stable complexes with copper salts. Hence, we surmised that there would be a stronger activation when the complexes with CuCl, CuCl 2 , or Cu(OTf) 2 were applied.…”

“…For this purpose, we have synthesized new Hoveyda-Grubbs-type metathesis catalysts bearing chelating units [bpa (10) or dmepa (11)] in their vicinity. By the individual complexation of the latter with different metal salts (Fe 3+ , Zn 2+ , Ag + , Cu + , and Cu 2+ ) we could induce an electron-withdrawing effect that resulted in higher activity of the catalyst.…”

“…The reaction rate was highly dependent on the strength of the formed individual complex and the resulting electron-withdrawing effect thereof. [10] Our present aim was to investigate if these electronic effects caused by the complexation of metal ions can also have an influence on the activity of catalytic systems.…”

Oxidative activation of dihydropyridine amides to reactive acyl donors

“…The product was isolated as a white solid (55.5 mg, 86%). 13 C-NMR major rotamer: 13 (14). 43 The general procedure A was followed with a total reaction time of 1 hour (including 30 min oxidation with DDQ).…”