Pentavalent Organoantimony Compounds as Mild N-Arylating Agents for Amines: Cu-Mediated Ullmann-Type N-Arylation with Tetraarylantimony(V) Acetates

Abstract

Simple and mild Cu-mediated arylation of various amines by use of tetraarylantimony acetate (Ar 4 SbOAc) is described. The Ullmann-type condensation of Ar 4 SbOAc with aliphatic and electron rich aromatic amines proceeded efficiently in the presence of copper(II) acetate. The arylation can be carried out under aerobic conditions without care of exogenous oxygen. This simple procedure exceeds the conventional Ullmann condensation which often requires harsh reaction conditions. Key words tetraarylantimony(V) acetate; N-arylation; Ullmann condensation; copper(II) acetate; aerobic reactionThe aryl-nitrogen bond can be found in a wide range of biologically active compounds such as bradykinin (BK) receptor antagonist martinellic acid 1) and opioid receptor agonist CJ-15161.2) Thus, it is desirable to develop simple and efficient methods for aryl-nitrogen bond formation. Among them, research on transition metal-catalyzed C-N bond formation has flourished recently. For example, remarkable progress in bulky and electron rich phosphine ligands has enabled Pd-and Ni-catalyzed cross-couplings of amines and alcohols with aryl halides and sulfonates.3,4) These transition metal-catalyzed reactions have been recognized as one of the most reliable methods for C-N bond formation.5-8) Direct C-H functionalization to form C-N bonds has also been another convenient entry for C-N cross-coupling using transition metal catalysts.9,10) However, these elaborated catalysts and phosphine ligands often tend to be sensitive to air oxidation and hydrolysis by moisture. These problems make the traditional Ullmann condensation attractive in large and industrial scale applications employing low price, non-toxic, and air-stable Cu reagents. [11][12][13][14] Because traditional Cu-mediated Ullmann condensation has been conducted and limited by harsh reaction conditions, 15) many improvements in Ullmann-type C-N bond formation have recently been made. For example, aryl halides employed as aryl donors in the traditional Ullmann condensation were replaced with highly reactive transmetallating agents such as organo-boron, 13,14,[16][17][18][19] -silicon, 20) -stannane, 19,21) -lead, 14,22) and -bismuth compounds.14, [23][24][25] In the course of our studies on organoantimony (Sb) compounds as synthetic reagents, we have recently demonstrated that Sb(III) compounds were efficient transmetallating agents for transition metal-catalyzed cross-coupling reactions. 26,27) We also reported that Sb(V) compounds work as useful pseudo-halides in Pd-catalyzed cross-coupling reactions. 28)These results stimulated us to employ them in Cu-mediated arylation of amines.As for Sb-mediated N-and O-arylation of amines and alcohols, triphenylantimony ortho-phenylenedioxides and triphenylstibane have been reported to function as aryl donors. 29,30) However, the reactions are not so efficient, in that they must be carried out using amines or alcohols as solvents at high temperature. Thus, we focused on highly reactive Sb(V) compounds as Cu-mediated N-arylating agents. 31,32...

The Complementary Competitors: Palladium and Copper in C–N Cross-Coupling Reactions

“…In addition to the best known representatives of this type, the derivatives of hypervalent iodine (iodonium salts), the main-group metals (Tl(III), Pb(IV), Bi(V)) are known to be capable of such transformations (Sb(V) was recently added). The derivatives of these three metals are known as mild arylating agents for a number of nucleophiles, in this respect resembling the hypervalent iodine compounds.…”

Copper-promoted S-arylation reactions with triarylbismuths for the synthesis of diaryl sulfides

“…Notably, sterically hindered substrates could be converted without any difficulty in the protocol, including 2-methyl, 2,4-dimethyl, 2-methoxy, and 1-naphthyl substituted compounds (3b, 3e, 3f and 3q). In view of hypervalent organoantimony compounds previously used as aryl donors in some coupling reactions, 22,23 we explored the feasibility of Ar 3 Sb in the current reaction. Fortunately, it is notable that Ar 3 Sb could act as an efficient arylating partner for the C-S crossing coupling as well, affording the desired products in 93-99% yields under the optimal reaction conditions (3a, 3c and 3l).…”

Synthesis, Structure and Applications of Hypervalent Organoantimony Compounds Having Intramolecular E→Sb (E = N, O, S) Coordinations

“…[2-(Me 2 NCH 2 )C 6 H 4 ] n R 3-n Sb [n = 1, R = Ph (5), Mes (6); n = 2, R = Ph (7), Mes (8), CH 2 SiMe 3 (9)] and [2-(Me 2 NCH 2 )C 6 H 4 ]PhMesSb (10) [50,51]. Compounds 5-10 exhibit chirality and crystallize as racemic mixtures.…”

“…However, triethylantimony is spontaneously flammable in air, and it is not until 1882 that the development of organoantimony chemistry began when air-stable triphenylantimony was synthesized by Michaelis and Reese [2]. Since then, a large number of organoantimony compounds of trivalent and pentavalent states were synthesized, and used in areas such as medicine [3], catalysis [4][5][6], organic synthesis [7][8][9][10] and ligand chemistry [11][12][13]. However, wide application is restricted due to the unstable nature of the compounds, a result of being air-sensitive and/or ligand scrambling.…”