Halogen-mediated oxidation

By contrast, a more direct and atomically efficient route for the production of aromatic amines would be to eliminate the need for halogen mediated oxidation of benzene. This can be achieved by a class of reaction known as nucleopWlic aromatic substitution for hydrogen (NASH-Figure 7). While this type of reaction has been known for over 100 years, this chemistry generally proceeds in low yields, give mixtures of ortho and para substitution products, and requires the use of environmentally unfavorable external oxidants.23 This section will focus on two new examples of NASH chemistry applicable to the production of commercially relevant aromatic amines. The... 

The halogen-mediated in-cell oxidation of ketones is a recently commercialized electrosynthesis. 

In order to obtain the desired macrocyclic diaiyl ethers, the effect of halogen substituents is utilized to control the directions of intramolecular cyclization reactions mediated by TTN. As shown in Scheme 166, on TTN-mediated oxidation of a compound... 

The sodium periodate-mediated oxidation of alkali halides is a useful method to accomplish the halogenation of aromatic compounds. Accordingly, NaCl is successfully employed as a chlorine source for the chlorination of various aromatic compounds, although mixtures of regioisomers are sometimes obtained on the other hand, the related sodium periodate-mediated bromina-tion reaction, which uses lithium bromide or sodium bromide as halogen source, affords the expected brominated products in a regioselective fashion (eq 33). ... 

Direct Alkynylation. Ni-catalyzed direct alkynylation on azoles has been achieved without assistance of halogen-mediated activation by using oxygen as oxidant in the catalytic cycle. TIPS-acetylene was added to a variety of nonhalogenated azoles to produce the Sonogashira coupling products (eq 25). ... 

We will focus on reagent-mediated oxidations and will therefore not cover electrochemical oxidations, though significant work has been done on the relevant reactions.This means we will not be covering Yoshida s cation pool method for the electrochemical generation of cations to which nucleophiles may be added,though some of the mechanistic details will overlap. Since a major benefit of CDC reactions is their one-pot nature we will deprioritize stepwise processes, for example Af-halogenations that can be used in Hofmann-Loffler-type cyclizations. ... 

As different research groups have shown, electrochemical reactions can be mediated by metal powders, metal ions, metal oxides, semi-metals, halogens, inter halogens, halogen oxides, organics, or organometallics [123]. 

The electrochemical oxidation of amines to imines and nitriles typically utilize a chemical mediator. The use of both Al-oxyl radicals [12, 13] and halogens has been reported for this process [14]. For example, the conversion of benzyl amine (14a) into nitrile (15a) and aldehyde (16a) has been accomplished using the M-oxyl radical of a decahydroquinoline ring skeleton as the mediator (Scheme 5). The use of acetonitrile as the solvent for the reaction generated the nitrile product. The addition of water to the reaction stopped this process by hydrolyzing the imine generated. A high yield of the aldehyde was obtained. In the case of a secondary amine, the aqueous... 

Indirect electro-oxidation of primary amines to nitriles is achieved using halogen ion as mediator [93]. The reaction is typically carried out in an undivided cell... 

The 14-electron species denoted here as Cp2M (M = Ti, Zr), generated from Group 4 metallocenes, mediate useful oxidative cyclizations of dienes 231 [103,104], enynes 233 [105] and diynes 235 [105,106] via the metallacycles 232, 234 and 236. These metallacycles are useful intermediates, which are hydrogenolysed, carbonylated, halogenated, attacked by electrophiles and converted to functionalized cyclic compounds such as 238 and 239 [107],... 

---