Hydrocarbons Ritter reaction

This procedure constitutes the first example of one-step conversion of a /-alkane to the corresponding /-alkyfamine. Other hydrocarbons in this class, such as isobutane, have also been aminated with good results.7 Only a very limited number of convenient routes, e.g., the Ritter reaction, are available for the preparation of /-carbinamines. The present preparation illustrates a simple method that utilizes a novel substrate. 

By analogy with their behavior in mass spectrometry, branched hydrocarbons are cleaved when oxidized in CH3 CN/TEABF4 at —45 °C. The resulting acetamides of the fragments (Table 6) are formed by cleavage of the initial radical cation at the C,C bond between the secondary and tertiary C atom, to afford after a second electron transfer, carbocations, which react in a Ritter reaction with acetonitrile [29]. 

The physical technique with the greatest potential for synthetic applications of Ritter-type reactions is electrochemistry. A selection only of examples is discussed here. Synthetic chemists unfamiliar with this technique will find the review by Eberson and Nyberg an informative and entertaining introduction to this area. Electrochemical Ritter reactions may be performed through anodic substitution of a hydrogen by the nitrile, followed by hydrolysis of the nitrilium ion intermediate, as shown in Scheme 42. The majority of reactions investigated have been anodic acetamidations using hydrocarbons, alkyl halides, esters or ketones as the substrate. In some cases, such as reaction of the adamantane derivatives (83), the yields of amide product are excellent (Scheme 43). 

The electro-oxidation of an aromatic hydrocarbon containing a benzylic hydrogen, using solutions of perchlorates, tetrafluoroborates, or hexafluorophosphates in acetonitrile as the electrolyte, results in the formation of an acetamido derivative. This is essentially the electrochemical analog of the Ritter reaction. Again direct oxidation of the aromatic molecule has been regarded as the initial step in the overall reaction, e.g., in the reaction with toluene (II) (Scheme 2). Increasing amounts of the nucleophile, water. 

The hydride abstraction reaction of NO+ has been employed in a modified Ritter-type reaction51 1 (Scheme 5.50, routea) as well as in ionic fluorination512 of bridgehead hydrocarbons (Scheme 5.50, route b). 

It was also found recently that direct selective substitution of aliphatic hydrocarbons via a supposedly electrophilic mechanism can be achieved by use of F-TEDA-BF4 [202]. Depending on the exact reaction conditions, either alkyl fluorides or Ritter-type products are obtained (Scheme 2.91). Relatively short reaction times favor the formation of the fluorides, longer heating with F-TEDA-BF4 in acetonitrile favors the formation of acetamides, especially in the presence of additional BF3 OEt2 as Lewis acid catalyst [203]. 

Several other reactions involving C-N bond formation have been reported. A Ritter-type reaction of alkylbenzenes with nitriles has been achieved. Thus, the treatment of ethylbenzene with CAN in the presence of a catal3dic amount of N-hydroxy-phthalimide (NHPI) in EtCN produces the corresponding amide in good selectivity (eq 23). The reaction is also applicable to a number of unactivated hydrocarbons. As a comparison, the photolysis of admantane with CAN gives a mixture of products. In another case, the oxidation of monoterpenes such as pinene with CAN in acetonitrile affords the corresponding bisamides in good yields (eq 24). ... 

---