Pseudohalides acyl chloride reactions

The so-called "ene" reaction has not been observed with phosgene, although it occurs readily with the related carbonyl pseudohalide, CO(CN)j [972]. Moreover, no Diels-Alder product is obtained when 1,3-cyclohexadiene is reacted with phosgene. Acyl chlorides are formed at 80 C and very high pressures, but no reaction occurs between 1,3-cyclohexadiene and COCl, at atmospheric pressure [1185]. 

Several reactive pseudohalides are available for catalytic reactions. Diazonium salts 2 derived from anilines, and phenyl triflates 3 and nonaflates (nonafluorobu-tanesulfonates) derived from phenols are highly reactive substrates. In addition, acyl chlorides 4, anhydrides 5, and sulfonyl chlorides 6 are also used. 

Occasionally reactions proceed with phosphine-free Pd(0) catalysts. Some phosphines are more expensive than Pd and more difficult to recover than Pd. Therefore, an ideal catalyst is a phosphine-free Pd(0) catalyst. Reactions of reactive halides and pseudohalides such as aryl iodides, diazonium salts and acyl chlorides proceed under phosphine-free conditions. 

Hexamethyl- and Hexabutylditin. These ditins undergo cross-coupling with a variety of organohalides and pseudohalides (such as aryl halides, vinyl triflates, acyl chlorides, and allyl halides) in this protocol to give the correponding tin compounds. The reaction is particularly useful for preparation of organotins with labile functionalities that are not compatible with other procedures. 

Mesylates are used for Ni-catalysed reactions. Arenediazodium salts 2 are very reactive pseudohalides undergoing facile oxidative addition to Pd(0). They are more easily available than aryl iodides or triflates. Also, acyl (aroyl) halides 4 and aroyl anhydrides 5 behave as pseudohalides after decarbonylation under certain conditions. Sulfonyl chlorides 6 react with evolution of SO2. Allylic halides are reactive, but their reactions via 7t-allyl complexes are treated in Chapter 4. Based on the reactions of those pseudohalides, several benzene derivatives such as aniline, phenol, benzoic acid and benzenesulfonic acid can be used for the reaction, in addition to phenyl halides. In Scheme 3.1, reactions of benzene as a parent ring compound are summarized. Needless to say, the reactions can be extended to various aromatic compounds including heteroaromatic compounds whenever their halides and pseudohalides are available. 

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