Carbon-nitrogen bond forming reactions cyclization

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

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... 

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 photocyclizations of halogenated A-benzyl-/ -phenethylamines576 are examples of reactions in which two aryl rings are connected by a chain of four atoms, one of which is a nitrogen atom. In the cases reported, one phenyl ring has a bromine atom and the other an iodine atom at the ortho position. As expected, products were formed via initial rupture of the carbon-iodine bond and these products still contained the bromine atom. In addition, however, some unexpected cyclization products were encountered, containing iodine instead of bromine. The formation of these products was ascribed to replacement of bromine by iodine in the intermediate cyclohexadienyl radicals. 

A selective sampling of the photochemical cycloaddition and cyclization chemistry of 2H-azirines has been outlined in this chapter. Some photochemical sequences increase molecular complexity more than others, but each seems to provide complex heterocyclic structures in a very efficient manner. Indeed, many of these photoreactions rapidly construct hetero-polycyclic systems that are difficult to produce in other ways. In contrast to their photochemical behavior, the major thermal reaction of 2H-azirines generally involves C(2)-N bond cleavage to form vinyl nitrenes which further react by either insertion into an adjacent C-H bond or else undergo addition across a neighboring rc-bond. The 27i-electrons of the carbon-nitrogen double bond of 2H-azirines can also participate in thermal symmetry-allowed [4- -2]-cycloadditions with a variety of substrates. It is clear from the above discussion that the chemistry of 2H-azirines is both mechanistically complex and... 

Intramolecular hydroamination/cyclization, the addition of an N-H bond across an intramolecular carbon-carbon unsaturated bond, offers an efficient, atom economical route to nitrogen-containing heterocyclic molecules (Equation 8.37). Numerous organolanthanide complexes were found to be efficient catalysts for this transformation [124, 125]. The real active intermediates are organolanthanide amides, which are formed by the rapid protonolysis reactions of precatalysts with amine substrates. The proposed catalytic cycle of hydroamination/cyclization of aminoalkenes is presented in Figure 8.37 [124]. 

In the coordination unsaturated compounds (which are able to coordinate with one or two ligands) such as the Wilkinson complex, an aldehyde carbonyl, nitrogen group of diazo compound and carbon-carbon unsaturated bond oxidatively add to the compounds, and the cyclization is liable to proceed by reductive elimination [98-102]. For example, 4-pentene-l-al derivative reacts in the presence of the Wilkinson complex to afford prostaglandin derivatives by cyclization [98,101]. When the reaction is performed with a chiral rhodium complex, the cyclization product is obtained in a high ee% yield [102]. The cyclization usually forms five or six-membered ring compounds, the reaction of a diazo compound with acetylenic... 

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