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16.9.1.1.3.1.2 Method 2: Cyclization of Diazotized 2-Acylanilines (The Borsche Synthesis)

DOI: 10.1055/sos-SD-016-00313

Haider, N.; Holzer, W.Science of Synthesis, (200416257.

Diazotized 2-acylanilines, for example 2-acetylanilines and 2-(haloacetyl)anilines, cyclize smoothly to give cinnolin-4-ols 19 (Scheme 9). This method is known as the Borsche synthesis[‌84‌] and represents the most versatile and widely employed route to the latter class of compounds. Many cinnolin-4-ols with a wide variety of substitution patterns have been obtained in this way. At room temperature, the cyclization reaction proceeds slowly, although it can be accelerated either by electron-withdrawing groups meta to the acetyl moiety, or by carrying out the reaction at higher temperatures, but in some cases this results in a lower yield.[‌85‌] Examples with R1=SOMe[‌86‌] or SO2X (X=OH, NH2, NHPh, NMe2, Me, Ph)[‌87‌] have also been reported. A more recent variation of the Borsche approach is the cyclization of triphenylphosphoranylidene compounds 20 into cinnolin-4-ones 21, which can be subsequently hydrolyzed to give cinnolin-4-ols 22 (Scheme 9).[‌88‌]

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References


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