Greene protocol

Water-based green protocol under conventional heating was used in another publication [112] to carry out three-component treatment between 3-substimted 5-aminopyrazoles, barbituric acids, and several isatines. The reaction gave up required spiroheterocycles 77 in excellent yields and purity (Scheme 33). 

Fig. 4.89 Green protocol for TPAP/NaOCI catalyzed oxidation of ethers.

Tu and co-workers [112, 115] elaborated a green protocol for the synthesis of polysubstituted indeno[ 1,2-6]-quinolines 69 via condensation of an aldehyde, 1,3-indanedione and an enaminone using p-toluene sulfonic acid as the catalyst in water under microwave irradiation. A series of 23 indeno[l,2-6]quinolines 69 was generated in excellent yields. The same authors have also described the microwave-assisted synthesis of these compounds in acetic acid as solvent (Scheme 53). 

Polshettiwar et al. [38] gave a novel, one-pot, solvent free, green protocol for the synthesis of 1,3,4-oxadiazoles (xLii) by the condensation of acid hydrazide and triethyl orthoalkanates (xLi) using solid supported Nafion NR50 and phosphorus pentasulphide in alumina as a catalyst. 

An efficient synthesis of amides by the Ritter reaction of alcohols and nitriles under MW irradiation was developed under solvent-free conditions (Scheme 8.36). This green protocol is catalyzed by solid-supported Nafion NR50 with improved efficiency and reduced waste production." ... 

In 2007, Schreiner applied his thiourea 8 in developing a green protocol for the protection of alcohols with tetrahydropyran (THP) under neat reaction conditions. Utilising the privileged A7,N -his[3,5-bis(tri-fluoromethyl)phenyl]thiourea and a polystyrene-attached analogue, high yields were observed even on a preparative scale. A remarkably broad substrate scope was examined, while high turnover numbers (100 000) and turnover frequencies (up to 5700 h ) were well established (Scheme 19.12). 

Yadav, J. S., Reddy, B. V. S., Sreedhar, R, Reddy, J. S. S., Nagaiah, K., Lingaiah, N. and Saiprasad, P. S. 2004c. Green protocol for the Biginelli three-component reaction Ag3PW,204oas a novel, water-tolerant heteropolyacid for the synthesis of 3,4-dihydro-pyrimidinones. Eur. J. Org. Chem. 2004 552-557. 

D. B. Ramachary, M. Kishor, K. Ramakumar, Tetrahedmn Lett. 2006, 47, 651-656. A novel and green protocol for two-carbon homologation a direct amino acid/KjCO -catalyzed four-component reaction of aldehydes, active methylenes, Hantzsch esters and alkyl halides. 

M. Saha, S. Roy, S. K. Chaudhuri, S. Bhar, Green Chem. Lett. Rev. 2008, 1, 99-102. Microwave-assisted ammonium formate-mediated synthesis of Hantzsch dihydropyiidines under solvent-free conditions—a green protocol. 

We trast that this chapter sufficiently illustrates the utihty of MCRs in aqueous media in the efficient assembly of heterocycles of varied stractural complexity and diversity. Water has proved to be a nseful solvent for a variety of transformations leading to the efficient constraction of ring systems. In some reactions, it was found that the reaction occnrs only in water and in many others higher yields were obtained in water than in organic solvents. In appropriate cases, water plays multiple roles including those of a reactant, a solvent and even a catalyst in the case of on water processes. We hope that the information contained here encourages the readers to make use of these green protocols for the efficient and eco-friendly constraction of novel heterocyclic frameworks. 

Yadav JS, Subba Reddy BV, Shubashree S, Sadashiv K, Krishna Rao DJ (2007) Organic synthesis in water green protocol for the synthesis of 2-aminofiiran derivatives. Mol Catal A Chem 272 128-131... 

Chavan HV, Adsul LK et al (2011) Polyethylene glycol in water a simple, efficient and green protocol for the synthesis of quinoxalines. J Chem Sci 123 477-483... 

Ranu B, Jana R (2005) Catalysis by ionic liquid. A green protocol for the stereoselective de-bromination of viciwaZ-dibromides by [pmImJBF, under microwave irradiation. J Org Chem 70 8621-8624... 

In 2011, Mamaghani et al. reported a convenient one-pot green protocol for the synthesis of 2-imino-l,3-thiazolidin-4-ones 44 [45] by the reaction of amines, isocyanates, aldehydes, and chloroform in the presence of sodium hydroxide under ultrasonic conditions (Scheme 9.23). TZD-based 2-Imino-l,3-thiazolidin-4-ones were synthesized in high yields (75-91%) and shorter reaction times (12-15 min). 

B. M. Choudary, B. Bharathi, C. V. Reddy, M. L. Kantam, and K. V. Raghavan, The first example of catalytic N-oxidation of tertiary amines by tungstate-exchanged Mg-A1 layered double hydroxide in water A green protocol. Chemical Communications (2001), 1736-7. 

In this chapter we will highlight the benefits and the importance of homogeneous gold catalysis in the search for green protocols. The purpose of this chapter is not to provide a comprehensive report on gold-catalysed... 

S. Paul, A.R. Das, An efficient green protocol for the synthesis of coumarin fused highly decorated indenodlhydropyridyl and dihydropyri-dyl derivatives. Tetrahedron Lett. 53 (2012) 2206-2210. 

S. Paul, P. Bhattacharyya, A.R. Das, One-pot synthesis of dihydropyrano[2,3-c]chromenes via a three component coupling of aromatic aldehydes, malononitrile, and 3-hydroxycoumarin catalyzed by nano-structured ZnO in water a green protocol. Tetrahedron Lett. 52 (2011) 4636-4641. 

SCHEME 10 Green protocol on a solid phase. MW, microwave. 

The 1,5-benzothiazepine ring system has seen various applications as pharmaceutical scaffold [85] and thus a number of synthetic approaches have been reported mostly involving condensation of 2-aminothiophenol with a, 3-imsaturated carbonyl compoimds, co-bromoacetophenone, or chalcones xmder some kind of acidic or basic catalysis. Recently, an efficient one-step IL-mediated green protocol for the regioselective synthesis of stereoisomeric 2-aryl-3-hydroxy-l,5-benzothiazepines-4-ones (Scheme 25) from the reaction of 2-aminothiophenol with glycidates has been reported [86]. The cis-isomer 124 was formed as the major product in 76-90% yield in [bbim]Br and 82-95% yield in [bbim]PF6. 

R. Hekmatshoar, S. Sadjadi, S. Shiri, M.M. Heravi, Y.S. Beheshtiha, Green protocol for synthesis of 1,5-benzodiazepines and 1,5-benzothiaz-epines in the presence of nanocrystaUine aluminum oxide, Synth. Commun. 39 (2009) 2549-2559. 

R.S. Jetti, D. Verma, S. Jain, An efficient one-pot green protocol for the synthesis of 5-unsubstituted 3,4-dihydropyrimidin-2(lH)-ones using recyclable amberlyst 15 DRY as a heterogeneous catalyst via three-component BigineUi-like reaction, ISRN Org. Chem. (2012) 1-8. 

T. Kadre, S.R. Jetti, A. Bhatewara, P. Pahwal, S. Jain, Green protocol for the synthesis of 3,4-dihydropyrimidin-2(lH)-ones/thiones using TBAB as a catalyst and solvent free condition under microwave irradiation, Arch. Appl. Sci. Res. 4 (2012) 988-993. 

A practical and high yielding application of DlB-induced oxidative [4+2] annulations of o-phenylenediamines 135 and electron-deficient alkynes 136 was described for the preparation of quinoxaline derivatives 137 (Scheme 30). The oxidative [4+2] annulations between diaminobenzene (4e center) and electron-poor alkynes (2e center) were successfully mediated by 1(111) reagent. Formation of quinoxalines was proposed to involve an initial generation of enamine which was likely to undergo DlB-mediated oxidative [4+2] annulations and aromatization. This metal-free and green protocol is very useful in the synthesis of diverse bioactive quinoxaline scaffolds (Scheme 30) [46]. 

Chavan and Degani [198] reported a green protocol for the synthesis of 4,6-disubstituted-3-cyano-2-pyridones 107 108 from cyanoacetamides and 1,3-dicarbonyl compounds or chalcones using IL xmder solvent-free conditions... 

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