Coupling reactions, development

Table 5.6 Iron-catalyzed aryl-aryl coupling reaction developed by Knochel s group.

Scheme 5.12 Iron-catalyzed C-N coupling reaction developed by Taillefer et al.

The Kumada Coupling was the first Pd or Ni-catalyzed cross coupling reaction, developed in 1972. 

S. R. Chemler, D. Trauner, S. J. Danishefsky, The R-Alkyl Suzuki-Miayura Cross-Coupling Reaction Development, Mechanistic Study, and Applications in Natural Product Synthesis, Angew. Chem. Int. Ed. Engl. 2001, 40, 4544-4568. 

Chemler, S. R., Trauner, D., Danishefsky, S. J. The B-alkyl Suzuki-Miyaura cross-coupling reaction development, mechanistic study, and applications in natural product synthesis. Angewandte Chemie, International Edition 2001,40,4544-4568. 

The nickel-catalyzed substitution of vinyl sulfides by Grignard reagents forms the basis of a procedure for the stereoselective synthesis of alkenes by sequential cross-coupling reactions developed by Naso and... 

The very large variety of aryl-aryl coupling reactions developed in the last decades exceeds the scope of this article. An excellent review on the formation of biaryls with special attention to the synthesis of biaryl natural products was published by Bringmann et al. [93 a] in 1990, further reviews on the Stille [94,95a], Suzuki [95], and Heck [78,79] coupling reactions appeared more recently. This survey will present some selected examples of aryl-aryl coupling and condensation reactions described in recent years with special attention on... 

The cross-coupling reactions developed over the past 50 years have now been recognized by Nobel prizes to Heck, Suzuki, and Negishi. The relevance of these reactions in synthesis is obvious by the enormous number of publications dealing with the applications for the formation of sp carbon to sp carbon bond formation. Perhaps for this reason, only a few examples will be presented here, as the cycloheptanoid skeleton is basically made up of sp carbon atoms. Certainly, the inherent creativity of the synthetic organic chemist will change this situation very soon. 

Mechanistically, while the reaction pathways of Pd-catalyzed systems have been properly investigated, the reaction pathway of Ni-catalyzed cross-couphng reactions remains relatively unexplored. On the basis of Stille s proposal [145] and the cross-coupling reactions developed by the Fu group, oxidative addition by a radical mechanism seems reasonable, as the stereogenic center is racemized... 

Organoraetallic chemistry has provided several important new methods to carry out carbon-carbon or carbon-heteroaiom bond formation. Such processes, termed coupling reactions, developed from early work by Tsuji and by Trost, now have a central place in organic chemistry and in the pharmaceutical industry. Among the most useful arc shown below. The reaction names are given because research papers often refer to them in this way. 

With benzene and its derivatives, the various types of coupling reactions developed in the last decades open highly reliable routes to a wealth of substitution patterns [46-49]. In most cases, however, the corresponding halogen compounds are needed as starting materials, which does not change the substitution problem. 

Another area of interest to the industrial sector is the development of a more efficient synthesis of biaryl compounds. This has been accompHshed using a Ni(II)-cataly2ed Grignard coupling reaction with an aryl haUde (86—89). 

One of the newer and more fmitful developments in this area is asymmetric hydroboration giving chiral organoboranes, which can be transformed into chiral carbon compounds of high optical purity. Other new directions focus on catalytic hydroboration, asymmetric aHylboration, cross-coupling reactions, and appHcations in biomedical research. This article gives an account of the most important aspects of the hydroboration reaction and transformations of its products. For more detail, monographs and reviews are available (1—13). 

Mechanisms of Coupling. Because the active coupling species is the ioni2ed coupler (35,52), the rate of the coupling reaction and hence its abihty to compete for oxidi2ed developer is dependent on the pH of the process, the piC or acidity of the coupler or less frequentiy the rate of coupler ioni2ation, and the reactivity of the resulting coupler anion with the QDI (40). 

In addition to its uses in photography and medicine, iodine and its compounds have been much exploited in volumetric analysis (iodometry and iodimetry, p. 864). Organoiodine compounds have also played a notable part in the development of synthetic organic chemistry, being the first compounds used in A. W. von Hofmann s alkylation of amines (1850), A. W. Williamson s synthesis of ethers (1851), A. Wurtz s coupling reactions (1855) and V. Grignard s reagents (1900). 

They have also developed a route to 2-allenylindole derivatives (98T13929). When prop-2-ynyl carbonates (76) are reacted with 73 in the presence of palladium catalyst, a cross-coupling reaction occurs to give 77a (46%) and 77b (45%). Under a pressurized carbon monoxide atmosphere (10 atm), the palladium-catalyzed reaction of 73 with 78 provides 79a (60%) and 79b (60%) (2000H2201). In a similar reaction, when the substrate is changed to aryl halides (80), 2-aryl-1-methoxyindoles such as 81a (70%) and 81b (60%) are prepared (97H2309). 

Due to their successful synthesis of 2-(4 -chlorophenyl)-4-iodoquinoline from the corresponding precursor acetylene, Arcadi et al. (99T13233) developed a one-step synthesis of 2,4-disubstituted quinolines via palladium-catalyzed coupling reactions. An example is the Heck reaction of 4-iodoquinoline (131) with a-acetamidoacrylate (132). This one-pot synthesis yielded adduct 133 in 50% overall yield after purification via flash chromatography. 

Cationic phosphine ligands containing guanidiniumphenyl moieties were originally developed in order to make use of their pronounced solubility in water [72, 73]. They were shown to form active catalytic systems in Pd-mediated C-C coupling reactions between aryl iodides and alkynes (Castro-Stephens-Sonogashira reaction) [72, 74] and Rh-catalyzed hydroformylation of olefins in aqueous two-phase systems [75]. 

The total synthesis of palytoxin (1) is a landmark scientific achievement. It not only extended the frontiers of target-oriented synthesis in terms of the size and complexity of the molecules, but also led to new discoveries and developments in the areas of synthetic methodology and conformational analysis. Among the most useful synthetic developments to emerge from this synthesis include the refinement of the NiCh/CrC -mediated coupling reaction between iodoolefins and aldehydes, the improvements and modifications of Suzuki s palladium-catalyzed diene synthesis, and the synthesis of A-acyl vinylogous ureas. 

Carbon-carbon bond formation reactions and the CH activation of methane are another example where NHC complexes have been used successfully in catalytic applications. Palladium-catalysed reactions include Heck-type reactions, especially the Mizoroki-Heck reaction itself [171-175], and various cross-coupling reactions [176-182]. They have also been found useful for related reactions like the Sonogashira coupling [183-185] or the Buchwald-Hartwig amination [186-189]. The reactions are similar concerning the first step of the catalytic cycle, the oxidative addition of aryl halides to palladium(O) species. This is facilitated by electron-donating substituents and therefore the development of highly active catalysts has focussed on NHC complexes. 

For that reason an intramolecular benzannulation was developed, which incorporates all components for the intramolecular alkoxycarbonylation into the naphthoquinone 105 [65]. Based on that strategy a short and convergent pathway for the synthesis of racemic deoxyfrenolicin 108 was accomplished. Xu et al. replaced the allylacetylene 100 in the reaction sequence for nanaomycin A by alkynoate 106. The benzannulation product 107 was an appropriate precursor for a subsequent tandem oxa-Pictet-Spengler cyclisation/DDQ-induced coupling reaction [66]. Following this strategy the total synthesis of enan-tiomerically pure deoxyfrenolicin could be accomplished (Scheme 48). 

Early development of the homo-coupling reactions of aryl halides involves the use of stoichiometric amounts of air-sensitive Ni(0) complexes.54 The reaction could also be realized with a catalytic amount of Ni(0) complexes formed in situ when a stoichiometric amount of Zn was present. Besides aryl iodides, tosylates,... 

Our group has recently developed an alternative method for alkyl-(hetero)aryl- as well as aryl-heteroaryl cross coupling reactions catalyzed by iron salts.3 4 This methodology was inspired by early reports of Kochi et al.5>6 on iron-catalyzed cross coupling of vinyl halides and is distinguished by several notable advantages. 

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