Current Organocatalysis - Volume 10, Issue 2, 2023

Ecofriendly Indium catalyzed synthesis of organic compounds finds various applications in health sectors, electronics, semiconductors, and many more. An efficient co-catalyst and oriented catalyst behavior of Indium has become a choice for many organic transformations. Its compatibility with water, showing nontoxic and nonreactive action, proceeds the reactions with ease. Focus on Indium metal-mediated important organic transformations in water, is visible during the last decades, resulting in diverse organic compounds with excellent yields This present mini-review highlights some important indium metal-mediated reactions in water, for the diverse synthesis of important organic compounds.

The last two decades have witnessed tremendous growth in organocatalysis, especially using proline and related catalysts in a wide range of organic processes. Along with this, the heterogenization of organocatalysts over suitable support systems also emerged as an effective approach for addressing some of the major drawbacks associated with classical organocatalysts. Polymer-immobilized catalysts, in particular, are extremely stable under reaction conditions with excellent recyclability and reusability. Moreover, this approach offers green chemistry standards and is, thereby, supportive of large-scale industrial manufacturing processes. This article summarises the developments using polymer immobilized prolinederived systems as efficient organocatalysts for various asymmetric transformations in Aldol, Michael, Mannich, cyclization reactions, etc.

Background: The present work describes sustainable Knoevenagel condensation reaction of aryl/ heterocyclic aldehyde with various active methylene derivatives such as malononitrile, dimedone, ethyl cyanoacetate, ethyl acetoacetate, barbituric acid, and thiobarbituric acid is reported. The protocol was developed using water extract of mango peel ash (WEMPA), an agrowaste that emerged as a greener solvent media and in combination with microwave irradiation gave high-yield product isolation. The method noticed added advantages for the reaction faster reaction rate, inexpensive extract media, simple work-up, and not required chromatographic purification. The present method synthesized various Knoevenagel condensation derivatives benzylidinemalononitrile, ethyl benzylidenecyanoacetate, ethyl benzylideneacetoacetate, benzalbarbituric acid, benzylidene-2-thiobarbituric acid, and 5,5-dimethylcyclohexane-1,3-diones were characterized by FT-IR, ¹H- & ¹³C-NMR, and mass spectrometry. Further, selected derivatives were investigated for their electrochemical studies using cyclic voltammetry, and showed comparable oxidation and reduction potential properties. Objective: The objective of this work is to develop a green methodology synthesis of various active methylene derivatives via Knoevenagel condensation to give the product of benzylidinemalononitrile, ethyl benzylidenecyanoacetate, ethyl benzylideneacetoacetate, benzalbarbituric acid, benzylidene-2-thiobarbituric acid and 5,5-dimethylcyclohexane-1,3-diones. Methods: We have demonstrated WEMPA as a greener homogenous agro-waste catalytic medium for the economic synthesis of Knoevenagel condensation products. The developed method was found robust, non-toxic and solvent-free with a simple work-up to give the target product. The selected derivatives were investigated for their electrochemical studies using the cyclic voltammetry method. Results: The agro-waste-based catalyst developed avoids the use of the external organic or inorganic base for the Knoevenagel condensation reaction under microwave irradiation. The described method found faster, eco-friendly, simple filtration and recrystallization excellent yield, and purity of the Knoevenagel product. Further, the selected compounds (8a-8d, 9a- 9d, 10a-10d, 11a,-11c, 12a, 12b, and 13a-13c) were subjected to electrochemical behavior studies and showed good oxidation and reduction properties. Conclusion: In summary, we have established an efficient, simple, inexpensive agro-waste based catalytic approach for the synthesis of benzylidinemalononitrile, ethyl benzylidenecyanoacetate, ethyl benzylideneacetoacetate, benzalbarbituric acid, benzylidene-2-thiobarbituric acid and 5,5- dimethylcyclohexane-1,3-diones derivatives under microwave irradiation described. The catalyst is agro-waste derived, which is abundant in nature and recyclable without loss of activity after the four-run of the reaction, thus making the present approach a greener one. The advantages of the approach are inexpensive, chemical base free, requiring no external metal catalyst, short reaction time, and simple work-up isolated excellent yields of the product. For the first time, herein, we reported the electrochemical behavior of the products prepared, and showed good oxidation and reduction properties, and these molecules will emerge as good antioxidant agents.

The stereoselective synthesis of putaminoxin 1, a biologically active natural phototoxic lactone has been synthesized from (R)-2-Propyloxirane and Hex-5-en-1-ol. The synthesis involves Jacobsen’s hydrolytic kinetic resolution and ring-closing metathesis as the key steps.