Current Organocatalysis - Volume 5, Issue 3, 2018

In recent times, organocatalysis has received considerable attention of the chemical community due to its multifaceted benefits in organic synthesis, and is regarded as one of the hot research topics in advanced organic chemistry. Organocatalysts offer an alternative platform to the conventional transition metal catalysis, thereby satisfying several green chemistry aspects. Organocatalytic reactions have already emerged as powerful tools in the construction of simple to complex molecular scaffolds, and this research field of topical interest is developing fast with newer concepts. During the recent past, camphor-10-sulfonic acid, commonly known as CSA, has served as a promising organocatalyst in performing a huge array of organic transformations. CSA is relatively safe, commercially available, and cheap. The present review, for the first-time, offers an up-to-date literature on the developments of CSA-catalyzed organic transformations.

Background: Alkali metal S-alkylthiosulfates and S-aryl thiosulfates are known as Bunte salts following its discovery as sodium S-ethylthiosulfate by Hans Bunte in 1874. Since then, various derivatives including selenium-containing Bunte salts have been prepared and used as a sulfursurrogates in different organic transformations. Additionally, they exhibit diverse biological activities as well as are used in self-assembled monolayers (SAM) on gold and other metals. Methods: New methods for the preparation of Bunte salts have been developed over the last two decades along with diverse procedures for organic transformations. Results: This review article has focused primarily on newer preparative methods of Bunte salts, diverse applications in various organic reactions establishing them as suitable and potential sulfur surrogates. Other applications such as their biological activities, use in making self-assembled monolayers on gold and other metals have also been discussed. Conclusion: Recent literatures on Bunte salts are presented to illuminate their importance in various fields. It is clearly evident that the Bunte salts and its congeners could be synthesized easily by different simple procedures as well as they can be suitably used to synthesize many important S-containing organic compounds. Other miscellaneous uses are also discussed in this article.

Background: Carbonyl groups are important functional groups and they play a key role in organic chemistry. This group needs to be protected in multistep synthesis against various reagents for a counter-reaction. The effort towards developing an efficient methodology for the protection of carbonyl functional group is always a demanding reaction. The protection of carbonyl compounds for inhibiting their chemical reactivity is an important operation in chemistry. In this paper, camphor sulfonic acid-catalysed protection of various carbonyl compounds is developed. This method is simple, environmentally friendly and yields products in high yields. Method: Commercially available camphor sulfonic acid is used as organo-catalyst for the protection of carbonyl functionality. This catalyst is also employed for the protection of carbonyl functionality as thioacetal/mixed ketal in excellent yield. The newly synthesize compounds are characterized using 1HNMR, 13C NMR and IR spectroscopy. Result: A diverse carbonyl functional group is protected in excellent yield under mild reaction conditions. Conclusion: We have developed an efficient organocatalysed protection method of carbonyl functionality applicable to wide range of substrates.

Background: Michael addition reaction is one of the most important and widely used reactions for making carbon-carbon or carbon-hetero bonds in organic synthesis. The reaction involves a facile attack of nucleophile to enone in a conjugated manner across a carbon-carbon double bond. We herein report an expeditious camphor sulfonic acid-catalyzed Michael reaction for the synthesis of different 3-substituted indole derivatives at room temperature. This method is convenient, environmentally friendly and produces products in high yields. Method: Commercially available camphor sulfonic acid is used as organo-catalyst to activate the reaction. The newly synthesized compounds are characterized by using 1HNMR, 13C NMR and IR spectroscopy. Result: A highly substituted 3-indoyle carbonyl compounds has been synthesized in excellent yield under very mild reaction conditions. Conclusion: We developed an environmentally benign synthetic method to access novel synthesis of substituted indoles under remarkably simple and high yielding reaction.

Methyl-2-formyl benzoate is known as a bioactive precursor in organic synthesis of compounds due to its variety of pharmacological activities namely antifungal, antihypertensive anticancer, antiulcer, antipsychotic and antiviral properties. As an active scaffold, methyl-2-formyl benzoate can be considered as a significant structure and an excellent precursor for the search of new bioactive molecules. Methyl-2-formyl benzoate is synthetically a versatile substrate, which can be used as a raw material for the preparation of medical products. Due to its significant in organic synthesis, the objective of this review is to discuss on the various synthetic routes for the preparation of methyl- 2-formyl benzoate (via two-step and one-step methodologies) and its importance as precursor for the preparation of compounds with pharmaceutical applications. This review is of importance in synthetic fields and pharmaceutical industry.

Background: Phosphorus ylides have less nucleophilic and are more stable than arsenic ylides. Due to less interactions of p-carbon orbital with d-arsenic orbital, arsenic ylides react more than phosphorus ylides in the same reactions. Kinetics and a mechanistic investigation of many reactions with TPP have been reported earlier. Herein, we have reported the kinetic results obtained by UV-vis spectrophotometry technique from the reactions between dialkyl acetylenedicarboxylate (DMAD, DEAD and DTAD), triphenylarsine (TPA) as a catalyst and N-H heterocyclic compounds. Methods: A kinetic study was followed for the present reaction using the UV-vis spectrophotometry method. 0.3 mL aliquot of 10-2 M solution of reactants 1 and 3 were pipetted into a quartz spectrophotometer cell, then 0.3 mL aliquot of 50-2 M solution of reactant 2 was added to the mixture according to the stoichiometry of each reactant in the overall reaction. During the whole reaction time, the reaction was supervised by recording scans of the entire spectra at 25°C. The wavelength of 290 nm was chosen to follow the kinetics studies. Results: The reaction followed second-order kinetics and the partial order with respect to dialkyl acethylenedicarboxylates 1 and N-H heterocycle 3 compounds was one and one. . The fourth step (k4) of the proposed mechanism was recognized as the rate-determining step. This is logical, because in step4 (k4), a tiny protic solvent such as methanol is able to rapid the rate of proton-transfer through a hard non- linear arrangement of TS4 from C1 towards C2. Both steric and inductive effects of different alkyl groups within the structure of dialkyl acetylenedicarboxylates (which participate in the first step1 (k1) of the reaction mechanism) had a significant role on the reduction of the reaction rate, because kobs depends on (k1). Conclusion: An electron withdrawing substituent group on the second ring of 5-chloro-2- benzoxazolinione speeds up the rate of reaction, opposite the way of 2-benzoxazolinione alone. The magnitude of ΔH#130; is larger than TΔS#130;, so the reactions are enthalpy- controlled. The large and very positive values of ΔS#130; imply that all reactions have dissociative process. In the case of triphenylarsine (TPA), kinetics and reaction mechanism was different from triphenylphosphine (TPP) in a similar reactions.

Background: The pyridinium based p-toluenesulfonic acid functionalized [Py(CH2)4 SO3H][CH3PhSO3] ionic liquid has been employed as eco128;friendly solvent cum promoter for the multicomponent domino heterocyclization of substituted 2-aminobenzothiazoles with 4-hydroxy-6- methyl-2-pyrone / 4-hydroxycoumarin and aryl aldehydes to produce benzothiazolo[2,3-b]pyrano [3,4-e]pyrimidin-4-ones and benzothiazole [2,3-b]chromeno[3,4-e]pyrimidin-6-one in excellent yields. Methods and results: Three-component synthesis of structurally diverse benzothiazolopyrano/ chromenopyrimidines, incorporating the privileged heterocyclic scaffolds of medicinal relevance has been carried out by the reaction of substituted 2-aminobenzothiazoles with 4-hydroxy-6-methyl-2- pyrone / 4-hydroxycoumarin and aryl aldehydes in pyridinium based p-toluenesulfonic acid functionalized ionic liquid. The Brønsted acidic ionic liquid could be reused five-times without a significant loss of catalytic activity. Conclusion: The protocol proves to be efficient and facile in terms of high yields, operational simplicity, reduced reaction time and ease of recovery of the reaction medium.

Background: A highly efficient eco-friendly route for the synthesis of pyrazole derivatives from readily available chalcones/1, 3-diketones and hydrazines in glycerol using sarcosine as a novel organopromoter has been developed. To the best of our knowledge this is the first report on the use of sarcosine as an organocatalyst in organic transformations. Results and Methods: This method manifests several attributes of green chemistry like atomeconomy, reusability of catalyst, short reaction time and an eco-friendly medium. Conclusion: The present protocol can serve as a valuable green alternative to the existing methods for the synthesis of targeted molecules.

Background: Herein we disclosed a clean and sustainable, one pot, multicomponent protocol for the synthesis of Benzopyrimido[4,5-b]quinoline in glycerol in the presence of malic acid. Methods: The reported strategy eliminates the use of hazardous transition metal catalysts, acid, base and volatile organic solvents, which negatively affect the environment. In addition present methodology has advantages of mild reaction conditions, wide substrate scope, operational simplicity, easy workup, cost effectiveness and high yields of desired products. Conclusion: We have presented an efficient malic acid promoted, environmentally benign synthetic route to highly functionalized benzo[f]pyrimido[4,5-b]quinoline derivatives.