Van Alphen-Hiittel rearrangement

Subsequently, the rearrangement product of 118, formulated earlier as 117, was also shown by two independent groups to be 128, proving 4//-pyrazoIes to be major products from the van Alphen-Hiittel rearrangement. 

Rearrangements of the van Alphen-Hiittel type, involving migrations of carbon-linked substituents around the ring, and characteristic of the 2H-and 3//-pyrroles, the 3H- and 4//-pyrazoles, and the 2i/-imidazoles, are rare among 4//-imidazoles because of lack of suitably substituted examples. A number of other thermal reactions are known, including the extensively studied rearrangements of structure types 2 and 21. 

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