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DOI: 10.1055/sos-SD-031-01513

Rück-Braun, K.; Priewisch, B.Science of Synthesis, (2007311321.

Activated (electron-rich) arenes undergo electrophilic displacement of hydrogen by nitrosating reagents. Substitution normally occurs para to an activating group, such as amino, alkoxy, or hydroxy, but when there is no activation nitrosation is usually difficult and, in the heteroaromatic series, only electron-rich hetarenes are nitrosated.[‌1‌] The most commonly employed nitrosating reagent is nitrous acid, derived from the action of an acid upon sodium nitrite. Depending on the conditions employed, the main electrophilic species are the nitrosonium ion (NO+) or the nitrous acidium ion (H2ONO+). Nitrosations with nitrous acid are 1014 times less effective than the corresponding nitrations.[‌5‌] This is commonly attributed to the poorer electrophilicity of the nitrosonium ion versus the nitronium ion (NO2+). However, studies of kinetic deuterium isotope effects suggest deprotonation of the Wheland intermediate (also known as a σ-complex) to be the rate-determining step (Scheme 2).[‌6‌,‌7‌]

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