Reaction of 3‐Amino‐2<i>H</i>‐azirines with 2‐Amino‐4,6‐dinitrophenol (Picramic Acid): Synthesis of Quinazoline‐ and 1,3‐Benzoxazole Derivatives

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<jats:title>Abstract</jats:title><jats:p>The reaction of 3‐(dimethylamino)‐2<jats:italic>H</jats:italic>‐azirines <jats:bold>1a–c</jats:bold> and 2‐amino‐4,6‐dinitrophenol (picramic acid, <jats:bold>2</jats:bold>) in MeCN at 0° to room temperature leads to a mixture of the corresponding 1,2,3,4‐tetrahydroquinazoline‐2‐one <jats:bold>5</jats:bold>, 3‐(dimethylamino)‐1,2‐dihydroquinazoline <jats:bold>6</jats:bold>, 2‐(1‐aminoalkyl)‐1,3‐benzoxazole <jats:bold>7</jats:bold>, and <jats:italic>N</jats:italic>‐[2‐(dimethylamino)phenyl]‐α‐aminocarboxamide <jats:bold>8</jats:bold> (<jats:italic>Scheme 3</jats:italic>). Under the same conditions, 3‐(<jats:italic>N</jats:italic>‐methyl‐<jats:italic>N</jats:italic>‐phenyl‐amino)‐2<jats:italic>H</jats:italic>‐azirines <jats:bold>1d</jats:bold> and <jats:bold>1e</jats:bold> react with <jats:bold>2</jats:bold> to give exclusively the 1,3‐benzoxazole derivative <jats:bold>7</jats:bold>. The structure of the products has been established by X‐ray crystallography. Two different reaction mechanisms for the formation of <jats:bold>7</jats:bold> are discussed in <jats:italic>Scheme 6.</jats:italic> Treatment of <jats:bold>7</jats:bold> with phenyl isocyanate, 4‐nitrobenzoyl chloride, tosyl chloride, and HCl leads to a derivatization of the NH<jats:sub>2</jats:sub>‐group of <jats:bold>7</jats:bold> (<jats:italic>Scheme 4</jats:italic>). With NaOH or NaOMe as well as with morpholine, <jats:bold>7</jats:bold> is transformed into quinazoline derivatives <jats:bold>5</jats:bold>, <jats:bold>14</jats:bold>, and <jats:bold>15</jats:bold>, respectively, via ring expansion (<jats:italic>Scheme 5</jats:italic>). In case of the reaction with morpholine, a second product <jats:bold>16</jats:bold>, corresponding to structure <jats:bold>8</jats:bold>, is isolated. With these results, the reaction of <jats:bold>1</jats:bold> and <jats:bold>2</jats:bold> is interpreted as the primary formation of <jats:bold>7</jats:bold>, which, under the reaction conditions, reacts with Me<jats:sub>2</jats:sub>NH to yield the secondary products <jats:bold>5</jats:bold>, <jats:bold>6</jats:bold>, and <jats:bold>8</jats:bold> (<jats:italic>Scheme 7</jats:italic>).</jats:p>

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