Ring fragmentation, formation

Morozov and co-workers electrochemically demonstrated the pyridazine ring fragmentation induced by electron transfer agents. This reaction proceeded by elimination of chloride ions, cleavage of the pyridazine ring, and the formation of phthalonitrile 202 from 201 <00MC34>. 

Treatment of l,3-thiazolium-4-olates 526 with aliphatic aldehydes yielded a series of highly functionalized azetidin-2-ones 527 (Equation 216) <2003JOC6338>. The formation of this compound has been explained by ring fragmentation of an initial [3+2] cycloadduct. 

The bicyciic radical is expected to quickly add O2 (Reaction 6) to form a bicyciic peroxy radical which subsequently reacts with NO to form a bicyciic oxy radical (Reaction 7). It is the subsequent reaction of the bicyciic oxy radical that leads to the formation of ring fragmentation products (Reaction 8) ... 

Fischer and Zollinger have studied the reaction of p-chlorobenzenediazonium chloride with 2-naphthol-l-sulfonate. A very interesting dependence of the reaction products and reaction rate on the solvent was observed The initiaUy formed complex 102 decomposes under ring fragmentation in aqueous base (see (44) in Sect. 2.2.3) it does not react in water, ethanol or dimethylsulfoxide, reacts very slowly in acetone or glacial acetic acid to give a small amount of azo compound 7dJ, while in dichloromethane, chloroform, benzene or pyridine quantitative, though slow, formation of the azo compoimd is observed. Ba on kinetic measurements an Sisil-type mechanism was postulated for the formation of the azo dye 103 from the CT-complex 102... 

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