Carbon-nitrogen bonds cyclizations

A few stoichiometric reactions that formed aromatic carbon nitrogen bonds in the presence of stoichiometric amounts of Pd(PPh3)4 had been reported by Boger and co-workers (Equation (3)).24-26 In the absence of base, the palladium(0) was apparently not regenerated. Pd(PPh3)4 failed to catalyze these reactions when used in a 1 mol.% quantity, but it did induce cyclization in good yield when it was used in stoichiometric amounts 24-26... 

The cyclizahon of amino alcohols should be an attractive method for the synthesis of N-heterocyclic compounds, mainly because they can be obtained in a single step and without the generation of wasteful byproducts. Carbon-nitrogen bond formation catalyzed by Cp lr complexes has been extended to the synthesis of N-hetero-cyclic compounds by the cyclization of amino alcohols. 

The electrochemical cyclization reaction is less successful with the N-(3-phenylallyl)acetanilide 60 which has two potential bond cleavage sites from the radical-anion [173]. Carbon-nitrogen bond cleavage with loss of a 3-phenylallyl radical, leaving an amide nitrogen anion, is favoured over carbon-chlorine bond cleavage. 

Most cyclizations described in this chapter involve a carbon-nitrogen bond as the final step. However, the A -amino compound 17 offers an example of a carbon-carbon bond formation to complete ring formation. Treatment of 17 with MeCOCH2COMe gives a mixture of products 18 and 19 (Equation 6) <2003CHE953>, with 19 obtained in very small amounts. 

Copper was also effective in the creation of carbon-nitrogen bonds. N-(o-halophenyl)-guanidines gave 2-aminobenzimidazoles in the presence of a copper-1,10-phenantroline catalyst system. While the iodo and bromo derivatives in the presence of the copper catalyst gave the cyclized product in 83% and 96% yields respectively, the analogous palladium catalysed transformation showed similar efficiency in both cases, resulting in 88% and 86% yields.52... 

Not only acetylene derivatives do undergo palladium catalysed intarmolecular carbon-nitrogen bond formation with amines. The similar reaction of olefins in a Wacker-type process also leads to ring closure. (0-Aminopentenes bearing a suitable leaving group in the 4-position were converted to pyrroles in a cyclization-isomerisation-elimination sequence (3.65.),82... 

The imino nitrogen atom is sufficiently nucleophilic to attack the carbon atom of the seleniranium intermediate. An interesting example of these reactions is the conversion of imidates into y-lactams reported by Toshimitsu and Uemura [88-90] and by other authors [91,92] which is illustrated in Scheme 24. The cyclization of 155 occurs through the formation of a carbon-nitrogen bond with the generation of the iminium salt 156. The success of this reaction is due to the use of PhSeBr as the selenenylating agent. In this way, in fact, the bromine... 

Intramolecular carbon-nitrogen bond formation can be used to assemble a range of nitrogen-containing aromatic heterocycles (e.g., indoles, benzimidazoles, pyrro-zoles, quinolines, etc.). An early example of the application of this chemistry to indoles vas reported by Watanabe, in the intramolecular cyclization of hydrazones with ortho-chloroarenes (Scheme 6.36) [46]. This reaction can be considered to... 

In addition to simply mediating the formation of carbon-nitrogen bonds, palladium catalysis can be used to construct these precursors in concert with cyclization. One example of this was demonstrated by Barluenga, where palladium catalysis is employed to form two separate bonds first the carbon-carbon bond via the arylation of the azaallylic anion of imine 19, followed by catalytic carbon-nitrogen bond formation (Scheme 6.38) [50]. 

Palladium-catalyzed carbon-nitrogen bond forming reactions also provide an efficient route to generation of these precursors for Heck cyclization. Jorgensen... 

In Chap. 4, the author describes a direct access to indole-fused tetracyclic compounds containing a 1,4-diazepine framework by copper-catalyzed domino three-component coupling, cyclization, and A -arylation, which involve the formation of one carbon-carbon bond and three carbon-nitrogen bonds. 

In conclusion, the author has developed a novel route to isoquinoline-fused polycyclic compounds by a four-component coupling and cascade cyclization strategy. In this reaction, the cyclization/oxidation step can be accelerated by use of an oxygen atmosphere, giving rise to improved yields of the cyclized products in many cases. Because this four-component reaction catalytically forms one carbon-carbon and four carbon-nitrogen bonds producing only H2O and H2 as the... 

In the year 2010, the group of Danishefsky reported the first asymmetric total synthesis of (-)-phalarine by using a Mannich reaction/Wagner-Meerwein rearrange-ment/cyclization cascade sequence (Scheme 13.9) [10], In this reaction cascade, one carbon-nitrogen bond, one carbon-carbon bond, one carbon-oxygen bond, and two new rings were formed. 

The key step of the acridone synthesis introduced by Coppola is the condensation of a A methylisatoic anhydride with the lithium enolate of a 2-cyclohexen-l-one. The formed diketo intermediate spontaneously cyclizes into a dihydroacridone, easily aromatized to the corresponding acridone. The versatility of this method, which enables carbon-carbon and carbon-nitrogen bond formation under very mild conditions, is illustrated by the efficient syntheses of the demethoxy analogues of natural fliro and pyranoacridones 319, 320), as well as by those of several naturally occurring alkaloids, including 10-methylacridone (30),... 

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