Synthesis of 2-hydroxy-3-(2-methyl-propenyl)-1,4-naphthoquinone and related oxime derivatives

• Main Authors: Patricia S. Oliveira, Celso A Camara
• Format: Article
• Language: English
• Published: Universidade Federal de Mato Grosso do Sul 2012-06-01
• Series: Orbital: The Electronic Journal of Chemistry
• Subjects: norlapachol; lapachol; lapachones; oxime
• Online Access: http://orbital.ufms.br/index.php/Chemistry/article/view/368

<div class="WordSection1"><p><em>The condensation reaction</em><em> of commercial 2-hydroxy-1 ,4-naphthoquinone <strong>1 </strong>(lawsone) with isobutyraldehyde <strong>2</strong> furnishs norlapachol <strong>3 </strong>(2-hydroxy-3-(2-methyl-propenyl) -1,4-naphthoquinone) with yields ranging from 66 to 93% depending on the different conditions tested, and a reaction temperature factor determinant for the formation of the desired product. It was treated with hydroxylamine hydrochloride in alkaline (NaOH) to provide the oxime <strong>4</strong> from regioselective modification of the carbonyl C-1 with 91% yield.</em><strong> </strong><em>The</em><em> regioselectivity of the reaction can be explained by analyzing the </em><em></em><em></em><em>different</em><em> resonance structures which can be seen that the carbonyl C-4 is less electrophilic than C-1. In this work was also obtained the oxime <strong>5</strong>, <strong>6</strong> and <strong>7</strong> from lapachol, αlpha and β-lapachone, respectively, in yields of 64-85%. The oximes of αlpha and β-norlapachone, <strong>8</strong> and <strong>9</strong> are in obtention. </em><em>All the products were analyzed by IR and NMR, and were observed that oximes of lapachol and norlapachol are isolated as E/Z mixtures. Two-dimensional NOE-type experiments of the corresponding acylated derivative will be made to help identify the proportion of the mixture.</em></p></div>