Carbon-heteroatom bond forming

The chiral naphthyloxazoline substrates can also be employed in asymmetric carbon-heteroatom bond-forming reactions with lithium amides, which provide unusual... 

Eormation in saturated 0-heterocycles via carbon-heteroatom bond-forming reductive elimination 98ACR852. 

Recently, interest in copper-catalyzed carbon-heteroatom bond-forming reactions has shifted to the use of boronic acids as reactive coupling partners [133], One example of carbon-sulfur bond formation is displayed in Scheme 6.65. Lengar and Kappe have reported that, in contrast to the palladium(0)/copper(l)-mediated process described in Scheme 6.55, which leads to carbon-carbon bond formation, reaction of the same starting materials in the presence of 1 equivalent of copper(II) acetate and 2 equivalents of phenanthroline ligand furnishes the corresponding carbon-sulfur cross-coupled product [113]. Whereas the reaction at room temperature needed 4 days to reach completion, microwave irradiation at 85 °C for 45 min in 1,2-dichloroethane provided a 72% isolated yield of the product. 

Miscellaneous Carbon-Heteroatom Bond-Forming Reactions... 

Scheme 3 shows the conceivable reaction sites of alkenylbismuthonium salts, alkynylbismuthonium salts, bismuth ylides, and bismuth imides in carbon-carbon and carbon-heteroatom bond forming reactions. In the initial step, nucleophiles (Nu) attack the positively charged bismuth(V) center, a-proton or (3-carbon (Scheme 3a, b) whereas electrophiles (El) attack the negatively charged a-carbon or a-nitrogen (Scheme 3c, d). Usually, the resulting bismuth(V) intermediates... 

OVERVIEW OF CARBON-CARBON AND CARBON-HETEROATOM BOND FORMING REACTIONS... 

In spite of their relatively young age palladium and nickel catalyzed carbon-heteroatom bond forming reactions, also known as the Buchwald-Hartwig reaction, have gained significant importance amongst synthetic... 

A significant part of the examples of transition metal catalyzed formation of five membered heterocycles utilizes a carbon-heteroatom bond forming reaction as the concluding step. The palladium or copper promoted addition of amines or alcohols onto unsaturated bonds (acetylene, olefin, allene or allyl moieties) is a prime example. This chapter summarises all those catalytic transformations, where the five membered ring is formed in the intramolecular connection of a carbon atom and a heteroatom, except for annulation reactions, involving the formation of a carbon-heteroatom bond, which are discussed in Chapter 3.4. 

The introduction of nucleophiles onto five membered heterocycles through non-catalyzed aromatic nucleophilic substitution is of little synthetic value, since the comparatively high electron density of the aromatic ring makes the nucleophilic attack unfavourable. The introduction of transition metal catalyzed carbon-heteroatom bond forming reactions overcame this difficulty and led to a rapid increase in the number of such transformations. 

Carbon-heteroatom bond forming reactions are also efficient in introducing amines onto other five membered heterocycles. 2-, and 3-bromothiophene were both coupled with diphenylamine using the highly active palladium-PlBih catalyst system. The reactions furnished the desired products in both cases, although the yield varied significantly with the substitution pattern (6.75.),106... 

The copper catalyzed carbon-heteroatom bond forming reactions are also efficient in the introduction of oxygen and phosphorous based substitutents onto the aromatic ring. 3-Iodopyridine was reacted with -butanol in the presence of 10 mol% copper(I) iodide and 20 mol% 1,10-phenantroline... 

The last example focuses not on the functionalization of heterocycles by a transition metal mediated carbon-heteroatom bond forming reaction, but the palladium catalyzed conversion of primary amines, including amino-heterocycles, into urea derivatives. A representative example, shown in 8.38., includes the reaction of an amino-carbazole derivative with morpholine, carbon monoxide and oxygen in the presence of catalytic amounts of palladium(II) iodide. The formation of the urea moiety proceeds with great selectivity and in high yield.49 The reaction works equally well for primary aliphatic and aromatic amines. 

Synthesis of Heterocycles via Carbon-Heteroatom Bond Forming... 

With the aid of transition-metal catalysis, heterocycle formations can be achieved not only by carbon-heteroatom bond forming cydizations of an acyclic molecule with a terminal group such as alcohols and amines, but also by intramolecular carbon-carbon bond forming reactions of an acyclic precursor containing one or more heteroatoms in its tether moiety. This section will briefly survey heterocycle synthesis via carbon-carbon bond formations. For details of ruthenium-catalyzed C-C bond formations, see other chapters of this book. 

BiX3-mediated carbon-heteroatom bond-forming reactions 440... 

Carbon-heteroatom bond-forming reactions using bismuthonium salts 449... 

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