Gomberg-Bachmann Reactions

Base-promoted radical coupling between an aryl diazonium salt and an arene to form a diaryl compound. 

Lead tetraacetate and periodic acid complement one another in their applicability as reagents for glycol cleavage. The water sensitive lead tetraacetate is used in organic solvents, while periodic acid can be used for cleavage of water-soluble diols in aqueous medium. 

The carbon-carbon double bond of an alkene 8 can be cleaved oxidatively, by a dihydroxylation reaction-glycol cleavage sequence  

This two-step sequence is a valuable alternative to the direct double bond cleavage by ozonolysis. 

Criegee, L. Kraft, B. Rank, Justus Liebigs Ann. Chem. 1933, 507, 159-197. 

Criegee, E. Hoger, G. Huber, P. Kmck, F. Marktscheffel, H. Schellenberger, Justus Liebigs Ann. Chem. 1956, 599, 81-125. 

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 112, Springer-Verlag Berlin Heidelberg 2009 

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 120, Springer International Publishing Switzerland 2014 

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In contrast to the Gomberg-Bachmann reaction, the intramolecular variant, the Pschorr reaction, is carried out in strongly acidic solution, and in the presence of copper powder. Diazonium biphenyl ethers are converted to dibenzofurans, e.g. 8 9 ... 

The Gomberg-Bachmann reaction is usually conducted in a two-phase system, an aqueous alkaline solution, that also contains the arenediazonium salt, and an organic layer containing the other aromatic reactant. Yields can be improved by use of a phase transfer catalyst. Otherwise yields often are below 40%, due to various side reactions taking place. The Pschorr reaction generally gives better yields. 

Dediazoniation refers to all those reactions of diazo and diazonium compounds in which an N2 molecule is one of the products. The designation of the entering group precedes the term dediazoniation, e. g., azido-de-diazoniation for the substitution of the diazonio group by an azido group, or aryl-de-diazoniation for a Gomberg-Bachmann reaction. The IUPAC system says nothing about the mechanism of a reaction (see Sec. 1.2). For example, the first of the two dediazoniations mentioned is a heterolytic substitution, whereas the second is a homolytic substitution. 

The Gomberg-Bachmann reaction is a method for arylation of aromatic compounds and quinones (Gomberg and Bachmann, 1924). Originally this reaction involved adding aqueous sodium hydroxide slowly to an intimate mixture of an aqueous solu-... 

See the two Gomberg-Bachmann reactions reported in Organic Syntheses (Kaslow and Summers, 1963 Gomberg and Bachmann, 1964). 

The homolytic aromatic substitution part of the Gomberg-Bachmann reaction is, in the opinion of the present author, not sufficiently well understood on the basis of positive experimental data. ... 

Gomberg-Bachmann reaction 62, 116, 189, 206, 253ff., 261, 273, 301 Gutmann donor numbers 375... 

The Pschorr reaction can take place by two different mechanisms, depending on conditions (1) attack by an aryl radical (as in the Gomberg-Bachmann reaction) or (2) attack by an aryl cation (similar to the SnI mechanism discussed on p. 853). Under certain conditions the ordinary Gomberg-Bachmann reaction can also involve attack by aryl cations. 

In this section we include the intramolecular arylation of the Pschorr type, the inter-molecular arylation (Gomberg-Bachmann reaction), the arylation of alkenes and alkynes (Meerwein reaction) and related processes. 

It is therefore not astonishing that in the Gomberg-Bachmann reaction, the intermolec-ular counterpart of the Pschorr synthesis, yields are generally low. The homolytic part of the Gomberg-Bachmann reaction is, in the opinion of March142 and of the present author, not sufficiently well understood on the basis of the experimental data. Galli117a does not discuss this problem in his review. 

Gomberg-Bachmann reaction, 2, 6 9, 7 Grundmann synthesis of aldehydes, 8, 5... 

Gomberg-Bachmann Reactions 5.1 Biphenyls New Aryl Radical Sources... 

With many heterocycles as substrates, radical substitutions can be successfully carried out under the conditions of phase-transfer Gomberg-Bachmann reactions [145]. Again, as above, mainly aryl and heteroaryl halides have recently been used as precursors for heterobiaryl compounds. A study including the arylation of a large number of heterocycles in the presence of tributyltin hydride and catalytic benze-neselenol led to the results that mostly biaryl products are obtained from nitrogen-containing heterocycles, whereas furan and thiophene gave partially dearomatized compounds [155]. 

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