Triple bonds heteroatom-carbon

There is only one type of compound in this category, substituted nitriles. It will be useful to divide the data sets for substituent effects at carbon-heteroatom triple bonds into two classes, substituted nitriles and heteroethynylene sets. 

Results of Correlations for Carbon-Heteroatom Triple-Bond Sets... 

Cyclodditions to Carbon-Heteroatom Triple Bonds. Transient electrophilic carbenes are known to react with nitriles to give transient46 or even stable nitrile ylides 30.47 No reaction of transient nucleophilic carbenes with nitriles has been reported. 

Abstract The use of A-heterocyclic carbene (NHC) complexes as homogeneous catalysts in addition reactions across carbon-carbon double and triple bonds and carbon-heteroatom double bonds is described. The discussion is focused on the description of the catalytic systems, their current mechanistic understanding and occasionally the relevant organometallic chemistry. The reaction types covered include hydrogenation, transfer hydrogenation, hydrosilylation, hydroboration and diboration, hydroamination, hydrothiolation, hydration, hydroarylation, allylic substitution, addition, chloroesterification and chloroacylation. 

Chapter 22 continues the study of carbonyl compounds with a detailed look at nucleophilic acyl substitution, a key reaction of carboxylic acids and their derivatives. Substitution at sp hybridized carbon atoms was introduced in Chapter 20 with reactions involving carbon and hydrogen nucleophiles. In Chapter 22, we learn that nucleophilic acyl substitution is a general reaction that occurs with a variety of heteroatomic nucleophiles. This reaction allows the conversion of one carboxylic acid derivative into another. Every reaction in Chapter 22 that begins with a carbonyl compound involves nucleophilic substitution. Chapter 22 also discusses the properties and chemical reactions of nitriles, compounds that contain a carbon-nitrogen triple bond. Nitriles are in the same carbon oxidation state as carboxylic acids, and they undergo reactions that form related products. 

Regiochemistry is ordinarily not a concern in the addition of nucleophiles to structures having carbon-heteroatom multiple bonds that are not conjugated with carbon-carbon double or triple bonds, because only 1,2-addition is expected. If the addition creates a new chiral center, however, then stereoisomeric addition products can be formed. Considerable interest in this area was sparked by a report by Cram that nucleophilic addition to ketones having chiral a carbon atoms gave unequal yields of the possible diastereomeric adducts. For example, addition of ethyllithium to the methyl ketone (+ )-92 gave primarily the erythro product (+ )-93. 

Insertion into Carbon-Heteroatom tr-Bonds. Shirakawa et al. reported the first example of insertion of arynes into a C—N bond. Using ureas as substrates a wide variety of 1-amino-2-(aminocarbonyl)arenes 86, including 1,4-benzodiazepine and 1,5-benzodiazocme derivatives, can be prepared (Scheme 12.45) [76]. Related to this work, Larock et al. developed the intermolecnlar C—N addition of amides across the aryne triple bond, providing access to (6>-anilino)triflnoroaceto-phenones 87. The presence of the CF snbstituent resulted to be crucial for the insotion process, which were limited to secondary snbstrates (Scheme 12.45) [77]. 

Monomers with carbon-carbon or carbon-heteroatom double bonds (e.g. an oxygen as in ketones) or triple bonds between carbon-carbon or carbon-nitrogen, can be polymerized. In this popular method of synthesis, the oldest one, the asymmetric center is in the lateral chain. 

Dipolarophiles utilized in these cycloadditions leading to five-membered heterocycles contain either double or triple bonds between two carbon atoms, a carbon atom and a heteroatom, or two heteroatoms. These are shown in Scheme 9 listed in approximate order of decreasing activity from left to right. Small rings containing a double bond (either C=C or C=N) are also effective dipolarophiles, but these result in six- and seven-membered ring systems. 

Step 1. ICs are defined as any carbons containing no double or triple bonds to heteroatoms. ICs isolate functional groups from each other according to the classical Hammett concept, so that the treatment of complex structures is simple. 

In fact, this heuristic principle (HP-8), which refers to nucleophilic heteroatoms directly attached to sp carbon atoms, may be also applied to nucleophilic heteroatoms directly attached to sp olefinic carbon atoms. In such cases, however, rather than a "disconnection" we would have an "unri-elimination" which will afford the substituted heteroatom as the "nucleofuge" and a triple bond as the "electrofuge". 

Most of the compounds that you have encountered in this text so far have been fairly simple. In addition to any carbon-carbon double or triple bonds, they have contained only one functional group and could be named by using suffixes such as -ynol or -dienone. However, for a compound that contains more than one heteroatom functional group, only one of these functional groups can be designated in the suffix. For example, consider the following compound, which has both alcohol and ketone functional groups ... 

Metal-mediated intramolecular addition of silyl enolates to alkynes is also valuable for the synthesis of cyclic ketones. A stoichiometric amount of HgCl2 or EtAlCl2 effectively promotes the cycloalkenylation via anti-addition to alkynes (Equations (87) and (88)).319 320a The -addition mode can be explained by a metal coordination to the triple bond and subsequent attack of the enolate moiety from the opposite side to the metal. The resultant alkenylmetals can be used for carbon-carbon and carbon-heteroatom bond formation as well as protonation. 

Besides carbon-halogen bonds, Bu3SnH is used routinely for hydrogenolysis of various carbon-heteroatom bonds. The deoxygenation from alcohols has been performed by a Barton-McCombie reaction where the addition of tin hydride to the triple bond is suppressed (Equation (2)).29-31... 

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