Carbon-heteroatom bond

Figure 10.3-40. The rating for the disconnection strategy carbon-heteroatom bonds is illustrated, Please focus on the nitrogen atom of the tertiary amino group. It is surrounded by three strategic bonds with different values. The low value of 9 for one ofthese bonds arises because this bond leads to a chiral center. Since its formation requires a stereospecific reaction the strategic weight of this bond has been devalued. In contrast to that, the value of the bond connecting the exocyclic rest has been increased to 85, which may be compared with its basic value as an amine bond.

The disconnection strategy Carbon-Heteroatom Bonds gives only one strategic bond, which is rated with a value of 100. 

You have already seen that a carbon-heteroatom bond is easy to make, since we used such bonds as natural places for disconnections (frames 234 ft). It is good strategy therefore to make a carbon-heteroatom bond and then to transform it into a carbon-earbon bond. The Claisen rearrangement is one way to do this an ortho allyl phenol (B) made from an allyl ether (A) ... 

The isomerization of vinyl- or ethynyl-oxiranes provides a frequently exploited source of dihydrofurans or furans, but analogous conversions of vinylaziridines have not been applied so often. While most of the examples in Scheme 87 entail cleavage of the carbon-heteroatom bond of the original heterocycle, the last two cases exemplify a growing number of such rearrangements in which initial carbon-carbon bond cleavage occurs. 

The advantage of starting with a ring of -1 members lies in the nature of the rearrangements, which proceed through cyclic transition states, so that the system never becomes open-chain — the carbon-carbon bond is broken only while the carbon-heteroatom bond is being made. 

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. 

Functionalization of pyridines via formation of carbon-heteroatom bond with elements of groups IV, V, and VI 99KGS437. 

Cyclic systems have frequently been used in studies of chemical bonding and reactivity, reaction mechanisms and a variety of other problems of interest to chemists3. Their utility depends on the changes in the carbon-carbon and the carbon-heteroatom bonds as well as on steric and electronic effects that result from the introduction of heteroatoms into the system. Indeed, the carbon-heteroatom bond length in small rings shows an effective increase with increasing heteroatom electronegativity4, in line with a... 

Transition-Metal-Based Carbon-Carbon and Carbon-Heteroatom Bond Formation for the Synthesis and Decoration of Heterocycles... 

Maes BUW (2006) Transition-Metal-Based Carbon-Carbon and Carbon-Heteroatom Bond Formation for the Synthesis and Decoration of Heterocycles. 1 155-211 Maiti M, Kumar GS (2007) Protoberberine Alkaloids Physicochemical and Nucleic Acid Binding Properties. lO. 155-210... 

Benzyl and Allyl Carbon Atoms Hydrogenolysis of a carbon-heteroatom bond is extremely fast if the heteroatom is connected to allylic or benzylic carbon atoms. The benzylic compounds are used very frequently in organic chemistry as protecting groups. Because of its great importance the benzylic compounds are discussed separately in the next section. 

Hydrogenolysis of the C-C bond takes place on different metal catalysts but the rupture of the nonpolarized C-C bond is more difficult than cleavage of the more polarized carbon-heteroatom bonds.482-486... 

Cross-coupling to form carbon heteroatom bonds occurs by oxidative addition of an organic halide, generation of an aryl- or vinylpalladium amido, alkoxo, tholato, phosphido, silyl, stannyl, germyl, or boryl complex, and reductive elimination (Scheme 2). The relative rates and thermodynamics of the individual steps and the precise structure of the intermediates depend on the substrate and catalyst. A full discussion of the mechanism for each type of substrate and each catalyst is beyond the scope of this review. However, a series of reviews and primary literature has begun to provide information on the overall catalytic process.18,19,22,23,77,186... 

During the cross-couplings to form C—N, C—O, C—S, and C—P bonds, the arylpalladium halide complexes are converted to arylpalladium amide, alkoxide, thiolate, and phosphide complexes. Examples of each type of complex have now been isolated, and the reductive elimination of the organic products has been studied. Although the reductive elimination to form carbon-hydrogen and carbon-carbon bonds is common, reductive elimination to form carbon-heteroatom bonds has been studied only recently. This reductive elimination chemistry has been reviewed.23... 

Among these reactions, the cycioadditions play a central role because of their general application, and for the unequalled property of the possible introduction of two new carbon-carbon or carbon-heteroatom bonds in the same step or process. 

Transition Metal-Catalyzed Carbon-Heteroatom Bond Formations... 

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... 

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