Isatogens synthesis

Pfitzinger synthesis, 2, 446 six-membered heterocycles from, 2, 92 synthesis, 4, 150 Isatogens... 

Whereas the condensation of o-iodonitrobenzene with copper acetylides is accompanied by cyclization into isatogens, neither 4-iodo-3-nitro- nor 5-iodo-4-nitro-l,3-dimethylpyrazole gives cyclized products in conditions of acetylide synthesis. Moreover, nitropyrazolylphenylacetylene, as compared with o-nitrotolane, does not undergo thermal, catalytic, or photochemical isomerization to give the fused five-membered rings. 

The intramolecular cyclization of a nitro group with a triple bond has been extended to the synthesis of six- and seven-membered ring compounds analogous to isatogens. Thus, the reaction of the acetylene group with the nitro group in 39 yields 2-phenyl-3-oxobenzo[prepared from the corresponding biphenyl derivative.19... 

The 1-hydroxyindoles (78 R = Ph, 2-pyridyl, C02Me) are rapidly oxidized by 4-nitroperbenzoic acid to the corresponding isatogens (79).18,47 The exploitation of this synthesis awaits the development of efficient general syntheses of 78. Recently an electrochemical method has been described.51 52... 

Preparations of cinnolines by expansion of five-membered heterocycle rings include the oxidation of A-aminooxindoles 232 (Scheme 132) <1988JHC847>, the treatment of isatogens 233 with ammonia (Scheme 133), and the base-catalyzed conversion of 1-aminodioxindoles 234 into cinnolin-3-ones 235 (Scheme 134) <1960JA4634>. Additional examples of the synthesis of cinnolines by transformation of another ring are available in CHEC-III . 

A further extension of this strategy has been employed as a route to carbazoles, as illustrated by the synthesis of the system 116 from the 2-nitrobiphenyl derivative 117 (Equation 30) <20040L533>. A substituted 2-nitrobiphenyl derivative has been cyclized to a carbazole using P(OEt)3 en route to the pyridocarbazole alkaloid ellipticine <2006HCA111>. It should also be mentioned that annulation of o-(alkynyl)nitrobenzene precursors with TBAF or pyridine gave access to indol-3-one-l-oxides (isatogens) <2003T2497>. 

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