Cu,Ni, andPdMediated Homocoupling Reactions in Biaryl Syntheses: TheUllmann Reaction

Abstract

The traditional Ullman reaction is the homocoupling of aromatic halides mediated by copper at elevated temperatures. Ullman first reported this reaction in 1901. Although the coupling conditions first reported are still widely used, a host of modifications have been made to these reactions. Some of these modifications include the use of activated and alternative metals, often resulting in much lower coupling temperatures. Nickel and palladium are the most utilized source of alternative metals, Periodic reviews have been published. This chapter covers the literature on copper, nickel, and palladium mediated homocoupling reactions in biaryl synthesis from 1901 to 2000. The focus of this chapter is the scope and limitation of these processes, preparation of the activated metal, and mechanism of the homocoupling process

The halogen bond with isocyano carbon reduces isocyanide odor

“…On the other hand, once working with the isocyanide adducts, the side reactions including iodoperfluoroarenes should be taken into account. Their most common transformation include, for instance, nucleophilic substitution of fluorine or/and iodine atoms [67][68][69] , metal-catalyzed C-C coupling 70 , reduction 71 , as well as metal-halogen exchange 72,73 . In addition, XB with isocyanides should electrophilically activate the isocyano group what could possibly promote the nucleophilic addition to the isocyano carbon, which is a typical reaction for some of metal-activated isocyanides 21 .…”

Stereospecific Approach to the Synthesis of Ring-A Oxygenated Sarpagine Indole Alkaloids. Total Synthesis of the Dimeric Indole Alkaloid P-(+)-Dispegatrine and Six Other Monomeric Indole Alkaloids

“…Within the area of intermolecular biaryl synthesis, the two most common approaches employed are: (1) oxidative coupling 52c and (2) reductive coupling such as Ullmann, 52,54 Suzuki, 52,55 Stille 52,56 or C- H activation 52,57 etc. Oxidative phenolic coupling is a powerful and economical method for the synthesis of biaryl compounds and is especially suited to natural product synthesis since many of the biosynthetic routes to biaryls involve such a coupling.…”

“…With the appropriate aromatic halides 36a and 37a in hand, the Ullmann reductive coupling 54 to form the C7-C7′ bond was first investigated. Similar to other reductive coupling processes, various protocols of the Ullmann-type coupling procedures have been developed; however, very few are suitable for atropselective synthesis of biaryls mainly due to the harsh conditions (multi-hour reactions at temperatures >100 °C) required to obtain high yields of the desired biaryl.…”

Recent advancement of Ullmann-type coupling reactions in the formation of C–C bond

“…The role of TBAB is very crucial for this process because it behaves simultaneously as the base, ligand and reaction medium. Moreover, the efficiency of Pd-catalysts has also been investigated in Ullmann coupling of bromopyridine and iodopyridine in presence of coreductants [15,16]. Here it is important to note that, Cai et al developed Pd(OAc) 2 catalyzed Ullmann reaction in microemulsion without other reducing agent [17].…”