Hetarynium ions

As noted in Section I.2.C, this review will cover five-membered hetarynium species such as 10 and 11 which are isoelectronic with arynes but in which the dehydro bond is exclusively between a carbon and a heteroatom and not between two carbon atoms. Such species may be cationic (10) or neutral (11) depending on the nature of the heteroatom. Hetarynium ions were first defined,proposed,and, in some cases, rejected as possible reaction intermediates in the six-membered pyridine system (9). The observed chemistry of 9 is that expected for either the a-pyridyl cation structure 9b or, preferably, the cyclic nitrilium ion form 9a. No uniquely arynelike properties have been reported, which accounts for the absence of hetarynium species from Hoffmann s monograph. ... 

The most likely route to five-membered hetarynium ions related to 10 is probably the dediazonization of the diazonium salts 641, a method which represents the single successful path to phenyl cations. With sulfur, oxygen,... 

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