[RhCp*Cl₂]₂-Catalyzed Directed N-Boc Amidation of Arenes “on Water”

Abstract

Rhodium(III) catalysis "on water" is effective for directed C-H amidation of arenes. The catalytic process is promoted by OH groups present on the hydrophobic water surface and is inefficient in all (most) common organic solvents investigated so far. In the presence of easily prepared tert-butyl 2,4-dinitrophenoxycarbamate, a new and stable nitrene source, the "on water" reaction can efficiently provide the desired N-Boc-aminated products with good functional group tolerance.

A comprehensive overview of directing groups applied in metal-catalysed C–H functionalisation chemistry

“…Concerning the formation of C–heteroatom bonds in 6-aryl-9 H -purines, three amidation methods were reported using electrophilic N -Boc O -acyl hydroxylamines or dioxazolones ( Scheme 156E–G ). 747 , 748 , 753 This last procedure, in particular, furnished high yields, and offers the possibility of thiophene functionalisation ( Scheme 156G ). Finally, trifluoromethylthiolation 727 and halogenation 962 were reported by Matsunaga/Yoshino and Pawar, both under Co catalysis ( Scheme 156H and I ).…”

“… 745 , 746 A reaction with the electrophilic nitrogen source N -Boc- O -2,4-dinitrophenylhydroxylamine in water under Rh catalysis was developed by Lu ( Scheme 124C ). 747 Notable features of this procedure are: the use of water as solvent, the good FG tolerance, and the possibility of functionalisation of purine-based nucleosides. Chang used a similar hydroxylamine reactant, N -Boc- O -acetylhydroxylamine, in the Co-catalysed amidation of arenes: in this case a variety of carbamates (other than N -Boc) could be employed in the reaction, and purines could be used as DG ( Scheme 124D ).…”

Directing‐Group‐Assisted Transition‐Metal‐Catalyzed Direct Intermolecular C−H Amidation and Amination of Arenes

“…A series of useful N ‐carbamate protecting groups, including Cbz, Moz, Ac, Boc, and even Fmoc, were successfully installed. Very recently, Lu's group reported a novel C−H amidation “on water” with a [RhCp*Cl 2 ] 2 catalyst activated by dangling OH groups present on hydrophobic water surfaces. tert ‐Butyl‐2,4‐dinitrophenoxycarbamate was introduced as a new, easily accessible and bench stable N ‐Boc amine source.…”

Rhodium(I)-catalyzed Decarbonylative Direct Olefination of 6-Arylpurines with Vinyl Carboxylic Acids Directed by the Purinyl N1 Atom

“…With assistance from the N1 atom, cobalt‐catalyzed C−H cyanation of 6‐arylpurines was reported by the same group . More recently, Lu and co‐workers described the N1‐directed C−H bond amidation of 6‐arylpurines “on water” under the catalysis of [RhCp*Cl 2 ] 2 . Given the importance of 6‐arylpurines in medicinal applications, it would be very attractive to install more functional groups in them through selective direct functionalization of C–H bonds.…”