Carbon-heteroatom bonds oxygenations

Besides the successful development of asymmetric syntheses with carbon-carbon bond formation, methods for carbon-heteroatom bond formation were also investigated intensively. In this context we developed several practical protocols for carbon-nitrogen, carbon-oxygen, and carbon-phosphorus bond formation. 

The palladium catalyzed iminoannulation and carboxyannulation of alkynes and an appropriate aryl/vinyl halide is an efficient tool to construct six membered nitrogen and oxygen heterocycles. The process encompasses the concomitant formation of a carbon-carbon and a carbon-heteroatom bond. 

Examples of the transition metal catalyzed formation of carbon-heteroatom bonds other than carbon-nitrogen are less abundant. In a recent survey of the copper catalyzed carbon-oxygen bond formation between alcohols and organotrifluroborates the coupling of 3-thienyltrifluoroborate and 2-furfuryl alcohol gave the expected thienyl-furfuryl-ether in good yield (6.83.),113... 

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 exchange of a halogen to a classical nitrogen or oxygen nucleophile usually proceeds readily on the purine skeleton, without the necessity of using a transition metal catalyst. There are certain cases, however, where the palladium catalyzed carbon-heteroatom bond formation might take preference over noncatalysed methods. Inosine derivatives, for example,... 

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. 

Substitutions such as alkylation (Chapter 5) and oxygenation (Chapter 9) are fundamental transformations essential to the chemistry of hydrocarbons. Other heterosubstitutions (i.e., formation of carbon-heteroatom bonds), such as halogenation, nitration, or sulfuration (sulfonation), are also widely used reactions. It is outside the aim of our book to discuss comprehensively the wide variety of substitution reactions (for a scope, see, e.g., March s Advanced Organic Chemistry), but it is considered useful to briefly review some of the most typical selected heterosubstitutions of hydrocarbons. 

Chapter 6 (Addition), Chapter 7 (Carbonylation), Chapter 8 (Acylation), and Chapter 10 (Heterosubstitution) deal with derivatization reactions to form carbon-heteroatom bonds. The important broad field of hydrocarbon oxidations is covered in Chapter 9 (Oxidation-oxygenation). Both the chemistry brought about by... 

Finally, cytochromes P-450 catalyze the oxidation of heteroatom-con-taining molecules, leading to products that derive either from the transfer of an oxygen atom to the heteroatom (N-or S-oxygenation) or from the oxidative cleavage of a carbon-heteroatom bond (N- or S-dealkylation) [46],... 

This reaction allows aryl carbon-heteroatom bond formation via an oxidative coupling of arylboronic acids, stannanes or siloxanes with N-H or O-H containing compounds in air. Substrates include phenols, amines, anilines, amides, imides, ureas, carbamates, and sulfonamides. The reaction is induced by a stoichiometric amount of copper(II) or a catalytic amount of copper catalyst which is reoxidized by atmospheric oxygen. 

The surface chemistry of carbon is of relevance to all aspects of catalytic carbon chemistry. The two most important heteroelements are hydrogen and oxygen. Each element can undergo a variety of chemically different coordinations which need to be discriminated in analyses of the chemical function of the carbon-heteroatom bond. In the literature the term surface complex is often used to described a group of chemically different bonds which could not be specified in detail. 

Reactions involving the formation of carbon heteroatom bonds include the industrially best known photochemical reactions. In fact, chlorination, bromination and sulfochlorination are major processes in industrial chemistry, and oxygenation has likewise an important role. Due to the focus on fine chemistry of this chapter, the discussion below is limited to laboratory-scale preparations and in particular to some bromination and oxygenation reactions illustrating the advantage of the photochemical approach, as well as to some alkoxylation, hydroxylation and amination reactions. 

Scheme 192. Reaction of Alkenyl Epoxides and Aziridines Producing Heterocycles via Carbon-Heteroatom Bond Formation by (a) Intramolecular Allylation of Oxygen and Nitrogen Nucleophiles and (b) Intermolecular [3 + 2]-Cycloaddition with Heterocumulenes...

Many flavoenzymes catalyze the oxidation of carbon—heteroatom bonds, where the heteroatom is usually nitrogen or oxygen. In these reactions, amines or alcohols are oxidized by the flavin. When nitrogen is the heteroatom, the resulting imine is hydrolyzed nonenzymatically. When the heteroatom is oxygen, a stable carbonyl is formed. 

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