Aroyl aryl-, various

Recent notable improvements by Knochel and co-workers include iron-catalyzed cross-coupling reactions of various acid chlorides 148 with dialkylzinc reagents (Equation (24))324 as well as the iron-catalyzed arylation of aroyl cyanides 149 with Grignard reagents (Equation (25)).3 5 In the first case Knochel s reaction conditions tolerate ester groups on the organozinc compounds, while in the latter case ester, aryl alkyl ether, cyano, and chloro functionalities on the aromatic moieties are compatibles with the reaction conditions. 

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. 

The reaction of pyrido[2,3-6]pyrazine (1) with various aromatic aldehydes in the presence of cyanide ion affords aryl pyrido[2,3-6]pyrazin-3-yl ketones 13 in low yield. This introduction of aroyl groups actually is not an acylation but rather a benzoin-like condensation with subsequent oxidation of the intermediate a-arylpyrido[2,3-6]pyrazine-3-methanol.78... 

One other feature of the data in Table 9.11 is worthy of further comment. Notice that alkyl (acetyl, propionyl)-substituted acylium ions exhibit a smaller o p ratio than the various aroyl systems. If steric factors were dominating the position selectivity, one would expect the opposite result. A possible explanation for this feature of the data could be that the aryl compounds are reacting via free acylium ions, whereas the alkyl systems may involve the more bulky acid chloride-catalyst complex. 

One other feature of the data in Table 10.10 is worthy of further comment. Notice that alkyl (acetyl, propionyl) substituted acylium ions exhibit a smaller o p ratio than the various aroyl systems. If steric factors were dominating the position selectivity, one would expect the opposite result. A possible explanation for this feature of the data could be that the aryl compounds are reacting via free acylium ions, whereas the alkyl systems may involve more bulky acid chloride-catalyst complexes. Steric factors clearly enter into determining the o p ratio. The hindered 2,4,6-trimethylbenzoyl group is introduced with a 50 1 preference for the para position. Similarly, in the benzoylation of alkylbenzenes by benzoyl chloride-aluminum chloride, the amount of ortho product decreases (10.3%, 6.0%, 3.1%, 0.6%, respectively) as the branching of the alkyl group is increased along the series methyl, ethyl, 2-propyl, t-butyl. ... 

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