New Greener Alternative for Biocondensation of Aldehydes and Indoles Using Lemon Juice: Formation of Bis-, Tris-, and Tetraindoles

Abstract

<p class="MsoNormal"> <span style="font-family:Verdana;">This work presents a new greener alternative for biocondensation of aldehydes and indoles for the synthesis of bis- and tris(indolyl)methanes catalyzed by lemon juice (</span><i><span style="font-family:Verdana;">Citrus limon)</span></i><span style="font-family:Verdana;"> in good yields under ultrasound irradiation in aqueous ethanol. Various substituted aldehydes with indoles under this reaction condition are elucidated. Also, tetraindolyl compounds were prepared using terephthaldialdehyde by following the same protocol. This method is an environmentally benign, efficient reaction, which requires shorter reaction time and simple experimental and work-up procedures.</span> </p

Visible light induced Knoevenagel condensation: A clean and efficient protocol using aqueous fruit extract of tamarindus indica as catalyst

“…In connection with our enduring interest concerning the investigation of new natural catalyst and development of new methodologies [55][56][57]63] we report herein a highly efficient and economic Knoevenagel condensation using a cooperative effect of visible light and aqueous tamarind juice. The strategy was applied for the condensation of different aldehydes and malononitrile (Scheme 1).…”

“…In literature, a number of organic reactions using natural catalysts such as clay [43][44][45][46], natural phosphates [47][48][49], animal bone [50], and various fruit juices are reported. Due to acidic nature aqueous fruit juice like lemon [51][52][53][54][55][56][57], pineapple [58], [59], coconut [60], Acacia concinna [61], Sapindus trifolistus [62] and Tamarindus indica [63] fruit has been found to be a suitable replacement for various homogeneous acid catalysts. Tamarind (Tamarindus indica) is grown extensively in Africa, South Asia, Northern Australia, South East Asia, Taiwan and China.…”

Visible Light Induced Knoevenagel Condensation Catalyzed by Starfruit Juice of &lt;i&gt;Averrhoa carambola&lt;/i&gt;

“…A number of organic reactions using natural catalysts such as clay [50]- [53], natural phosphate [54] [56], animal bone [57], and also various fruit juice's are reported in literature. Due to acidic nature, aqueous fruit juice like lemon [58]- [64], pineapple [65] [66], coconut [67], Acacia concinna [68], Sapindus trifolistus [69] and Tamarindus indica [70] [71] fruit has been found to be a suitable replacement for various homogeneous acid catalysis. In accordance with this, we report the Knoevenagel condensation of aromatic aldehydes with malononitrile in presence of aqueous starfruit juice, a natural, green and biocatalyst system stimulated by visible light.…”