Cross-coupling reactions Negishi couplings

A cross-coupling reaction (Negishi coupling) between A -SEM-pyrrol-2-yl-zinc chloride 618 and the appropriate dibromo derivative catalyzed by a Ni catalyst leads to 2-[4-(l//-pyrrol-2-yl)phenyl]-l//-pyrroles 619 (Scheme 125) <1997CM2876>. The SEM-protecting group can be easily removed by reaction with BU4NF. 

The cross-coupling via Negishi coupling was enabled through a number of palladium catalysts, some of which are shown in Figure 5-12. In particular, the commercial available POPd2 system by Li is stable and can be used for a number of other cross-coupling reactions (Scheme 5-102). 

Despite being activated by the nitrogen atom, 2-chloroquinoline (25) is still a poor substrate for the Stille cross-coupling reactions, though yields are usually improved under Negishi conditions. For instance, the coupling of... 

Knochel et al. described Pd-catalyzed Negishi cross-coupling reactions between zinc organometallics and aryl iodides in [BMMlM][Bp4]. Scheme 5.2-20 illustrates the reaction for the formation of a 3-substituted cyclohexenone from 3-iodo-2-cyclo-hexen-l-one [82]. 

Negishi E, Tan Z (2005) Diastereoselective, Enantioselective, and Regioselective Carbo-alumination Reactions Catalyzed by Zirconocene Derivatives. 8 139-176 Netherton M, Fu GC (2005)Pa]ladium-catalyzed Cross-Coupling Reactions of Unactivated Alkyl Electrophiles with Organometallic Compounds. 14 85-108 Nicolaou KC, King NP, He Y (1998) Ring-Closing Metathesis in the Synthesis of EpothUones and Polyether Natmal Products. 1 73-104 Nishiyama H (2004) Cyclopropanation with Ruthenium Catalysts. 11 81-92 Noels A, Demonceau A, Delaude L (2004) Ruthenium Promoted Catalysed Radical Processes toward Fine Chemistry. 11 155-171... 

Cross-coupling reactions with Zn acetylenides are the most convenient and selective routes to terminal acetylenes. In this reaction Zn is markedy superior to other metals, including Sn (24).116 The higher reactivity of Zn acetylides allowed assembly of hexaethynylbenezenes in two steps, with the last three groups introduced at the second stage by the Negishi reaction (25).117... 

Scheme 6.40 Negishi and Kumada cross-coupling reactions.

Scheme 6.42 Synthesis of enantiopure 2,2 -diarylated 1,1 -binaphthyls utilizing stereoconservative Negishi cross-coupling reactions.

E.-i. Negishi, in Metal-Catalyzed Cross-Coupling Reactions (Eds. F. Diederich,... 

Negishi, E.-L Liu, F. In Metal-Catalyzed Cross-Coupling Reactions 1998, Diederich, F. Slang, P. J. eds. Wiley-VCH Weinheim, Germany, pp 1-47. (Review). 

When the metallic additive to the intermediate 374 was zinc dihalide (or another Lewis acid, such as aluminum trichloride, iron trichloride or boron trifluoride), a conjugate addition to electrophilic olefins affords 381 . In the case of the lithium-zinc transmetallation, a palladium-catalyzed Negishi cross-coupling reaction with aryl bromides or iodides allowed the preparation of arylated componnds 384 ° in 26-77% yield. In addition, a Sn2 allylation of the mentioned zinc intermediates with reagents of type R CH=CHCH(R )X (X = chlorine, bromine) gave the corresponding compounds 385 in 52-68% yield. ... 

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