Azo Coupling Reactions of Aliphatic Diazonium Ions and Related Processes

1 Azo Coupling Reactions of Aliphatic Diazonium Ions and Related Processes 

Diazo Chemistry II Aliphatic, Inorganic and Organometallic Compounds. By Heinrich Zollinger Copyright 1995 VCH Verlagsgesellschaft mbH ISBN 3-527-29222-5 

The first azo coupling products of simple (i. e., not bridgehead) compounds were detected by Nesnow and Shapiro (1969), when they allowed l,2-dihydro-6-hydroxy-pyridin-2-one (6.3) to react with a large excess of diazomethane (1 100) in ether. They isolated l,2,3,6-tetrahydro-l-methyl-2,6-dioxopyridine-3-one methylhydrazone (6.4) in addition to the expected products of N- and O-methylation (6-2). 

An analogous result was reported by Testaferri et al. (1975) for the reaction of diazoethane with the thieno[3,2-Z ]thiophene derivative 6.5, where 011-ethylation and azo coupling in 3-position are observed. 

Nesnow and Shapiro and Testaferri et al. assume that the diazoalkanes are first protonated, in the case of l,2-dihydro-6-hydroxypyridin-2-one by the proton of the hydroxy group, with the thienothiophene derivative due to the tautomerism 6.5 6.6, i.e., by one of the protons of the methylene groups in 3- and 5-position of 6.5 and 6.6, and the formation of an intermediate ion pair of type 6.7. 

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