Coupling reactions palladium

Allyl- and vinylsilane chemistry was one of the first areas of reagent synthesis impacted by CM methodology. Allylsilanes are commonly employed in nucleophilic additions to carbonyl compounds, epoxides, and Michael acceptors (the Sakurai reaction) vinylsilanes are useful reagents for palladium-coupling reactions. As the ubiquitous application of CM to this substrate class has recently been described in several excellent reviews, this topic will not be discussed in detail, with the exception of the use of silane moieties to direct CM stereoselectivity (previously discussed in Section 11.06.3.2). 

The same group developed an interesting intermolecular palladium-catalyzed alienation of aryliodide with N-tosyl o-iodoanilines with nucleophiles in combination with two palladium-coupling reactions [69]. In this reaction, the N-allyl(2-iodopalladium)aniline intermediate 52 underwent an intramolecular Heck reaction followed by a cross-coupling reaction with phenyl boronic acid to give the 3,3-disubstituted indoline 53 in 78% yield (Scheme 8.27). 

Molander has published a series of papers demonstrating the utility of potassium alkyl, alkenyl-, alkynyl-, and aryltrifluoroborates in palladium coupling reactions. The crystallinity and air-stability of these trifluoroborate salts make the use of these an interesting alternative to the use of boronic acids or esters. Good yields have been obtained in several related palladium coupling processes, which are most easily classified as Suzuki couplings. The broad applicability of this process is demonstrated by the production of 58 [40], 59 [41], and 60 [42]. 

Because 3-chloropyridazines were not found to be very reactive in palladium coupling reactions and the bromo and iodo analogues are not readily available, the preparation and use of triflate esters of pyridazines have been developed. The readily prepared triflates undergo coupling with terminal acetylenes in the presence of palladium and copper iodide (Equation (27)). Reactions are rapid, normally complete in 0.5 to 6 hours at room temperature, and yields are high. In a comparative experiment 3-chloro-4-methyl-6-phenylpyridazine with 3,3-dimethyl-3-hydroxy-l-propyne gave only a 33% yield of 3-(3,3-dimethyl-3-hydroxy-l-propynyl)-4-methyl-6-phenylpyridazine after 12... 

Organic synthesis via palladium coupling reactions Pyatt, D. 

The two following syntheses of discodermolide by Smith and by Marshall joined a C9-C14 vinyl iodide with a C15-C21 iodozinc reagent in a palladium coupling reaction. 

Figure 3.6 Structure offerrocenylphosphine-amidine ligand for palladium coupling reaction...

An organobase including guanidine is often used as co-catalyst (or base) in palladium coupling reactions [84]. The 2-methylenepropane-l,3-diol diacetate reacts with 7,8-dihydroquinoline derivative in the presence of palladium acetate [Pd(OAc)2], TMG (1) and triphenylphosphine (PPhs) to give the methylene bridged compound in 92% yield, which can be converted to a diamino analogue of huperzine A, an inhibitor of acetylcholine esterase [84a](Scheme 4.32). 

Thus, traMi-3-alkyl-6-(phthalimido)cyclopentenes were prepared in excellent to modest yields from the corresponding tran -chloroalkene by the palladium coupling reaction [84d]. Inexpensive and efficient Pd-TMG systems, Pd(OAc)2-TMG or PdC -TMG, have been developed for the Heck reaction of an olefin with an aryl halide, in which TMG (1) acts as a ligand [84e]. In the reaction of iodobenzene with butyl acrylate the turnover numbers were up to 1000000. TMG (1) was used as a base for the palladium catalysed asymmetric Wagner-Meerwein shift of nonchiral vinylcyclopropane and cyclobutane derivatives leading to asymmetric synthesis of cyclobutanones, cyclopentenones, y-butyrolactones and 5-valerolactones [85] (Scheme 4.34). Replacement of TMG (1) with an inorganic bases such as lithium or cesium carbonate resulted in little effect. 

As ionic liquids are stiU expensive in comparison with conventional molecular solvents, their efficient recycling is an important issue that addresses the economics of their use, especially in large-scale applications. The most studied examples are the 1,3-dialkylimidazolium-based ionic liquids where the ionic solvent is usually recycled through several cycles of the reaction. Numerous examples describe the immobilization of a transition metal catalyst in the ionic liquid phase of a biphasic system. A variety of palladium coupling reactions, such as the Heck [27], Suzuki... 

RBA values were also measured for ERp and were usually lower. To achieve optimal synthetic yields, the mechanisms of a range of palladium coupling reactions (Sonogashira, Stille) were investigated [139]. 

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