Sustainable Approach to Waste-Minimized Sonogashira Cross

Research Article pubs.acs.org/journal/ascecg

Sustainable Approach to Waste-Minimized Sonogashira CrossCoupling Reaction Based on Recoverable/Reusable Heterogeneous Catalytic/Base System and Acetonitrile Azeotrope Vadym Kozell,† Michael McLaughlin,† Giacomo Strappaveccia,† Stefano Santoro,† Lucia Anna Bivona,‡,§ Carmela Aprile,§ Michelangelo Gruttadauria,‡ and Luigi Vaccaro*,† †

Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Via Elce di Sotto, 8, 06123 Perugia, Italia Dipartimento di Scienze e Tecnologie Biologiche, Chimiche e Farmaceutiche (STEBICEF) Sez. di Chimica, Università di Palermo, Viale delle Scienze s/n, Ed. 17, 90128 Palermo, Italy § Laboratory of Applied Material Chemistry (CMA), University of Namur, 61 rue de Bruxelles, 5000 Namur, Belgium ‡

S Supporting Information *

ABSTRACT: In this contribution, we present a chemically efficient and sustainable protocol for the palladium-catalyzed copper-free Sonogashira cross-coupling reaction, based on the use of a heterogeneous catalytic system. This consists in the combination of a palladium catalyst on highly cross-linked thiazolidine network on silica and a polystyrene-supported base. The solid catalyst/base system acts as a palladium scavenger avoiding leaching of the metal and consequent product contamination. The reaction can be conducted in safe and easily recoverable acetonitrile/water azeotrope as reaction medium. This proved to be an efficient greener alternative to the classic toxic aprotic media commonly used in cross-coupling reaction, such as DMF and NMP. Acetonitrile/water azeotrope could be easily recovered and reused allowing the minimization of waste production. Our approach, based on the use of both a supported base and a supported catalyst, has proven to be efficient for the waste reduction, as proved by the low E-factor values achieved. KEYWORDS: Azeotrope media, Green chemistry, Sonogashira reaction, Heterogeneous catalysis, Waste minimization

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INTRODUCTION

Our continuous interest in the development of environmentally friendly procedures for metal-catalyzed transformations led us to study the use of heterogeneous palladium sources in different cross-coupling and C−H activation processes.17−19 In this context, we have been paying attention to the definition of efficient protocols that simplify the isolation of the pure product and also minimize waste production by combining the use of recoverable and safer reaction media and heterogeneous reagents and catalysts. Specific efforts have been devoted to the design of efficient heterogeneous catalytic systems based on silica,20,21 zirconium phosphate22 and polystyrene supports23−28 that under the reaction conditions could be easily recovered and reused preserving the catalytic activity. In the past decade, particular attention has been dedicated to the development of new supported ionic liquid-like phases (SILLPs) with high Pd loading that were successfully applied in different reactions in batch as well as in flow reactors, providing significant waste minimization and low leaching of palladium into the products.20,22,29−32 Recently, we showed that a highly cross-linked thiazoliumbased material can be obtained by radical oligomerization of a bisvinylthiazolium dibromide salt in the presence of 3-

The Sonogashira cross-coupling reaction was developed in 1975 by Sonogashira, Tohda and Hagiara as an improvement of Heck and Cassar protocols for the preparation of alkynes.1−3 Since 1975, the Sonogashira reaction became one of the most representative and widely employed reactions allowing the synthesis of acetylenic compounds as precursors or as target molecule used in various fields.4−10 In a classical Sonogashira reaction, in addition to a main metal catalyst (typically palladium), a copper(I) halide is used as a cocatalyst to increase the reactivity and allow the reaction to proceed in milder conditions. Later, copper-free protocols have been proposed in order to reduce the side issue of alkyne oxidative homocoupling, known as Hay/Glasser reaction, which is observed in the presence of oxygen and of a Cu(I) cocatalyst.11−14 Although a copper-free approach to the Sonogashira reaction is typically less effective, there are obviously significant advantages in terms of product purification and reuse of a single catalyst. The usually lower catalytic activity can be compensated by higher reaction temperatures and the use of more reactive substrates such as aryl iodides,15 or more efficient palladium catalysts.16 © 2016 American Chemical Society

Received: September 9, 2016 Published: September 23, 2016 7209

DOI: 10.1021/acssuschemeng.6b02170 ACS Sustainable Chem. Eng. 2016, 4, 7209−7216

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ACS Sustainable Chemistry & Engineering

organic solvents are then required for the reaction workup, and acetonitrile as a common dipolar aprotic solvent is needed to wash the heterogeneous catalyst. In addition, a column chromatography purification to isolate the pure products is typically necessary. These experimental features are found in most of the reported protocols and well represent how minimal could be the impact on the whole sustainability of the process by simply replacing an organic reaction medium with water or a homogeneous catalyst with its heterogeneous counterpart. A proper and detailed quantification of the sustainability level reached should be always reported to evaluate properly the results achieved.30,44

mercaptopropyl-modified silica SBA-15. This new material is an excellent support for palladium species, which was used as a new catalyst for Suzuki and Heck reactions (Scheme 1).31 Scheme 1. Thiazolidine-Based Heterogeneous Palladium Catalytic System 1

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EXPERIMENTAL SECTION

Materials. Unless otherwise stated, all solvents and reagents were used as obtained from Sigma-Aldrich Co. without further purification. GC analyses were performed by using an Agilent 6850 equipped with a capillary column DB-35MS (30 m, 0.53 mm), a FID detector and hydrogen as gas carrier. GC-EIMS analyses were carried out by using a Hewlett-Packard HP 6890N Network GC system/5975 Mass Selective Detector equipped with an electron impact ionizer at 70 eV. NMR spectra were recorded on a Bruker DRX-ADVANCE 400 MHz (1H at 400 MHz, 13C at 100.6 MHz and 19F at 376.4 MHz) in CDCl3 using TMS as the internal standard. Elemental Analyses were conducted on a Fisons EA1108CHN. Melting points are not corrected, and they were measured on a Büchi 510. Inductive coupled plasma-optical emission spectrometry (ICP-OES 710 Agilent Technology) was used to determine the amount of leached palladium into the reaction products. Catalyst 1 was prepared according to the known procedure.31 Preparation of Polystyrene Supported Piperazine (PSpiperazine, 8). Merrifield resin (4.0 g, 200−400 mesh, 3.5−4.5 mmol/g Cl loading, 1% cross-linked with divinylbenzene) was reacted with piperazine (10.0 g, 0.115 mol, 99% purity) in toluene (40 mL) at 60 °C for 72 h. The resin was washed with a 0.5 M solution of piperazine in toluene, then toluene, water and acetone to remove the excess of amine and finally dried under vacuum. The amine loading (3.37 mmol/g) was determined by elemental analysis. Typical Procedure for the Sonogashira Reaction in CH3CN/ H2O Azeotrope Using Soluble Base (N-Methylpiperazine, 2). The reaction was performed in a screw capped vial with a magnetic stirrer. Catalyst 1 (10 wt % of Pd) (0.1 mol %), CH3CN/H2O azeotrope (1 M with respect to aryl iodide, 84/16 wt %), 1-methylpiperazine (2) (1.13 mmol), aryl iodide 5 (0.94 mmol) and alkyne 6 (1.41 mmol) were consequently added, and the resulting mixture was purged with N2 gas for 5 min under stirring. The resulting mixture was left under stirring at 90 °C. After reaction completion, ethyl acetate was added and the reaction mixture was filtered off and washed with water (3 × 1.5 mL). The organic layer was dried over anhydrous Na2SO4 and the solvent was removed under vacuum. Product 7 was purified by silica gel column chromatography using petroleum ether as eluent. Typical Procedure for the Sonogashira Reaction in CH3CN/ H2O Azeotrope Using Heterogeneous Base (PS-piperazine, 8). The reaction was performed in a screw capped vial with a magnetic stirrer. Catalyst 1 (10% wt. of Pd) (0.1 mol %), CH3CN/H2O azeotrope (1 M with respect to aryl iodide, 84/16 wt %), PS-piperazine (8) (1.13 mmol), aryl iodide 5 (0.94 mmol) and alkyne 6 (1.41 mmol) were consequently added, and the resulting mixture was purged with N2 gas for 5 min under stirring. The resulting mixture was left under stirring at 90 °C. After reaction completion, 1 mL of acetonitrile/water azeotrope was added and the reaction mixture was stirred for 5 min, centrifuged for 2 min (5000 rpm) and the liquid was separated by decantation. Then, 1 mL more of acetonitrile water azeotrope was added to the catalyst−base mixture and stirred for 2 min, centrifuged for 2 min (5000 rpm) and the liquid was separated by decantation. Resulting liquid phases were combined, and the solvent was removed under vacuum to yield the product. For details about the recycling procedure, see the Supporting Information.

As a continuation of our previous efforts in the development of sustainable approaches for cross-coupling reactions, we have extended our study to the definition of a waste-minimized protocol for the Sonogashira reaction.33 We have therefore investigated the most efficient reaction conditions for the Sonogashira cross-coupling reaction based on the use of thiazolidine-based heterogeneous palladium catalytic system 1 (Scheme 1). The use of such a kind of heterogeneous Pd-based catalyst has never been reported for the Sonogashira reaction. One of the main issues related to classic cross-coupling protocols concerns the use of harmful dipolar aprotic solvents such as NMP and DMF.34−37 This class of solvents nowadays is under strict regulation because of their toxicity and environmental impact. Their impact in terms of waste production is even higher if we consider that they are often used as aqueous mixtures.38,39 In addition, even when a solid catalyst is used in coupling reactions, amide dipolar aprotic solvents strongly bind to catalytically active metal catalysts, such as palladium, facilitating their dissolution with a consequent significant leaching into the product. Keeping in mind these facts, we focused our attention on the use of a safer reaction media, which could be easily recovered and reused allowing waste minimization. One of the recommended solvents to replace DMF and NMP is acetonitrile.40 In addition, the use of aqueous organic media is often beneficial when both organic and inorganic reagents are required. Therefore, on the basis of our experience on the use of aqueous conditions,41,42 we are proposing the use of acetonitrile/water azeotrope as a greener reaction medium that can be easily removed, distilled and reused.22,32 The use of azeotropes is also an effective approach that allows the recovery of water, a solvent that is usually ideal for safety reasons but that normally requires costly purification procedures if its regeneration is required.38 It is worth mentioning that protocols for the copper-free and phosphine-free Sonogashira reaction using sole water as reaction medium have been reported,15,43 but besides the intrinsic safety of water as reaction medium a clear advantage in terms of global sustainability is yet to be proven. In fact, as in the recent and representative protocol reported by Nasrollahzadeh et al, sole water can be used for running the Sonogashira coupling, but 7210


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RESULTS AND DISCUSSION Catalytic system 1 was prepared following our procedure31 and it has been used in an initial investigation aimed at the identification of the appropriate base able to allow a high chemical efficiency. Attention has been particularly devoted to those bases that could be also easily immobilized on a solid support in a later stage. At this aim, we selected Nmethylpiperazine (2), N-methylpiperidine (3) and triethylamine (TEA) (4) (Scheme 2). These bases can be anchored to a solid support by nucleophilic reaction of the corresponding secondary amines.44−46

purification by column chromatography was required. In addition, we tested two different phenylacetylenes containing a −CF3 group: in the sterically hampered ortho-position (6b) or in para-position (6c). In all the cases, high yields (89−91%) have been achieved without additional purification. To verify the possibility of improving the sustainability of the Sonogashira protocol based on the catalytic system 1, we prepared the polymer-supported counterpart of N-methylpiperazine by immobilizing piperazine on a chloride polystyrene resin (200−400 mesh, 3.5−4.5 mmol/g Cl loading, 1% DVB crosslinked) (see SI), which is known as a useful polymeric support in solid-phase synthesis as well as a support for catalysts, bases and acids.23−28 Loading of PS-piperazine (8) has been measured by elemental analysis. To investigate the efficiency of our completely heterogeneous catalytic system, a variety of aryl iodides 5 and terminal alkynes 6 have been tested (Table 3). In general, the use of immobilized base 8 in combination with catalyst 1 led to the formation of the expected products in good to excellent yields. The differences in reactivity observed for different substrates mostly depends on the substitutions featured by the aryl iodide. Very high reactivity was observed for 4-nitro-1-iodobenzene (5i), which afforded the corresponding clean product in very high yield (91%) after 6 h. Very importantly, thanks to the use of a heterogeneous base, there was no need for column chromatography purification. Aryl iodides with electron withdrawing groups (activated iodides) are more reactive than aryl iodides with electron donating groups or iodobenzene (5a). Only when iodobenzene (5a) or iodotoluene (5e) are used the product yields are significantly lower (77% and 62%, respectively) and formation of byproduct is observed, with the consequent obvious need for column chromatography purification. We also investigated the possibility to reuse the catalyst in 5 catalytic cycles for the Sonogashira coupling on the representative reaction of 4-iodoacetophenone (5d) with phenylacetylene (6a) using soluble (2) or heterogeneous base (8) (Figure 1). When the homogeneous base has been used, at the end of the reaction the mixture was centrifuged for better precipitation of the catalyst and the product was separated by decantation (see the Experimental Section and Supporting Information for further details). The catalyst has been washed twice with a small amount of CH3CN/H2O az., dried and reused for subsequent catalytic cycles. When PS-piperazine (8) was used, both base and catalyst were obviously recovered as a mixture after filtration and the base was regenerated by adding 1.5 equiv, relative to the limiting reagent, of N-methylpiperazine (see Supporting Information for details). The catalytic mixture (PS-piperazine (8) and catalyst 1) has been dried and reused for the next catalytic cycles. When catalyst 1 and supported base 8 were used, the catalytic system could be recycled for five consecutive reaction runs without observing any loss of catalytic activity (TON = 1250). On the other hand, when soluble base 2 was used, the recycling of palladium catalyst 1 was far less efficient, with an observed loss of catalytic activity already in the second cycle. A tentative explanation for this different behaviors can be put forward by considering that the heterogeneous base could also act as a palladium scavenger, avoiding the leaching of palladium into the products and thus preventing the deactivation of the catalytic system. We also analyzed the leaching of palladium in the crude products using inductively coupled plasma, optical emission spectroscopy (ICP-OES) analysis (Table 4). The results reveal a

Scheme 2. Different Organic Bases Selected for Sonogashira Reaction

A preliminary screening (Table 1) proved that catalyst 1 is effective in promoting the representative reaction of iodobenTable 1. Sonogashira Reaction Catalyzed by 1 in CH3CN/ H2O az. Using Soluble Bases*

entry

base

time for total conversion (h)

1 2 3

N-methylpiperazine (2) N-methylpiperidine (3) triethylamine (4)

5 6 8

*

Reaction conditions: iodobenzene (5a) 1 mmol, phenylacetylene (6a) 1.5 equiv, cat. (1) 0.4 mol %, base 1.2 equiv. Reaction medium: CH3CN/H2O az. (1 M), 90 °C.

zene (5a) and phenylacetylene (6a) with complete conversion. N-methylpiperazine (2) proved to be the most suitable base giving complete conversion to 7a in only 5 h. This result is interesting also in view of the immobilization of N-methylpiperazine that in its heterogeneous version is also known in literature as a basic catalyst for Gewald reaction,47 as an efficient catalyst for aldol reactions,48 as well as a deblocking-scavenging agent for an amino-protecting group.49 To explore and confirm a more general efficiency of catalyst 1 in the Sonogashira reaction, the protocol using N-methylpiperazine at 90 °C was extended to a variety of iodo-substrates 5 and different terminal alkynes 6 (Table 2). Under these reaction conditions, activated aryl iodides with electron withdrawing substituents (5b, R1 = NO2; 5c, R1 = COOCH3, 5d, R1 = COCH3) completely reacted without formation of any byproducts, affording the corresponding alkynes in very high yield (95−98%) by simple filtration of the catalyst and extraction of iodide ammonium salt. We extended the protocol also to aryliodides with electron donating substituents (−CH3, −OCH3), still obtaining very satisfactory although slightly lower yields (80−85%). Heterocyclic 2-iodothiophene 5h gave the corresponding product in very good yield (91%), but unfortunately 7211


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ACS Sustainable Chemistry & Engineering Table 2. Sonogashira Reaction between Aryl Iodides 5 and Terminal Alkynes 6 Using Soluble Base 2*

* Reaction conditions: 1.5 equiv of alkyne (6), 1 equiv of iodide (5), 0.4 mol % of the catalyst, 1.2 equiv of N-methylpiperazine (2). Solvent: CH3CN/H2O az. (1 M), 90 °C. aTime for the complete conversion of 5. bIsolated yield of the pure product. cPure product obtained without column chromatography.

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ACS Sustainable Chemistry & Engineering Table 3. Sonogashira Reaction between Aryl Iodides and Terminal Alkynes Using Heterogeneous Base (8)*

*

Reaction conditions: 1.5 equiv of alkyne, 1 equiv of iodide, 0.4 mol % of the catalyst, 1.2 equiv of PS-piperazine (8). Solvent: CH3CN/H2O az. (1 M), 90 °C. aTime for the complete conversion of 5. bIsolated yield of the pure product. c2.5 equiv of phenylacetylene. dPure product obtained without column chromatography.

Performing the reaction with immobilized base 8 led to the isolation of the desired product with 30 ppm of palladium (see Table 4). Although this value is relatively low, especially when compared to the one obtained from the reaction promoted by base 2 (315 ppm), it should still be considered that homogeneous palladium in extremely small amounts has been shown to be able to act as a catalyst.50 Thus, we decided to test the role of the leached palladium in our process by stopping the reaction between substrates 5d and 6a when 60% conversion was reached and performing both a mercury test and a hot-filtration test (see the Supporting Information for details). Although the addition of elemental mercury completely stopped the reaction, the removal of the solid catalyst significantly slowed down the process. These results suggest that the catalysis is mostly effected by palladium nanoparticles and that small homogeneous palladium species may play only a marginal role in the process. As an additional assessment of the sustainability of the protocols reported, we have also calculated the E-factor values associated with the preparation of 7 based on the use of a homogeneous or heterogeneous base. In the case of PSpiperazine (8) the E-factor values are in the range 8−20, whereas in the case of N-methylpiperazine (2) the range is 50−

Figure 1. Reuse of homogeneous (blue) and heterogeneous base (red).

significantly higher palladium content in the products obtained from the reaction performed with the soluble base (2), in line with our hypothesis that the supported piperazine (8) could act as a palladium scavenger. This aspect is crucial considering that, besides the number of the cycles, the actual durability of a metal catalyst is directly related to the extent of metal-leaching into the products. 7213


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ACS Sustainable Chemistry & Engineering Table 4. Palladium Leaching When Heterogeneous or Soluble Bases Are Used for the Preparation of 7d

leaching of Pd into products, compared to the protocol using a soluble base. In addition, acetonitrile/water azeotrope has been used as an easily recoverable reaction medium to replace highly toxic dipolar aprotic solvents often used in the Sonogashira reaction, such as DMF and NMP. The use of azeotropes represents an interesting and promising approach, because they are recoverable and reusable and thus allow the reduction of waste production. Moreover, the use of both a supported base and a heterogeneous catalyst allowed in general the isolation of the pure products without time-consuming and wasteful workup procedures, with a dramatic impact on the sustainability of the process. This is evidenced by the lower E-factors calculated for this procedure, in the range 8−20, compared to 50−100 of the protocol using a soluble base.

106 (see the Supporting Information for details). Clearly, the use of a heterogeneous catalyst/base system is more effective in terms of overall efficiency and waste minimization, allowing also the isolation of the pure products with a lower palladium content. As a representative example to evaluate the influence of the different contributions to the waste production, we report here the details for the E-factor calculation for the preparation of 7c, which did not require purification by column chromatography. Using a homogeneous base: E-factor = [769 mg {reaction solvent} + 114 mg {2} + 254 mg {5c} + 147 mg {6a} + 818 mg {azeotrope for washing} + 4485 mg {EtOAc} + 4500 mg {H2O} + 1500 mg {Na2SO4} − 218 mg {product 7c})/218 mg (product 7c)] = 57. While using a heterogeneous base: E-factor = [(254 mg {5c} + 147 mg {6a} + 143 mg {2, used for the regeneration of 8} + 120 mg {5% of azeotrope not recovered by distillation} + 1636 mg {azeotrope for washing} − 207 mg {product 7c})/207 mg (product 7c)] = 10. By considering the different contributions to E-factor calculations, it is evident that the very low waste production associated with our protocol using a heterogeneous base is mainly due to the efficient recovery and reuse of the azeotropic reaction medium. This medium combines the advantage of an aqueous organic solvent with the possibility of being easily recoverable. The overall waste is reduced by ca. 82% compared to our protocol making use of a homogeneous base. At this point, we have also tentatively approached the calculation of representative E-factor values for reported procedures making use of heterogeneous catalytic systems and/or safer reaction media as water.43 A major issue is related to the lack of data available in the literature for such processes. In a representative case where water has been used as a safer/cleaner medium,43 after process completion polymer-supported catalyst was isolated by filtration and it was washed with not quantified H2O and MeCN, the solvent was removed under vacuum, and then a typical column chromatography was needed to afford the pure product. Quantity of the solvents can only be guessed, but certainly E-factor values in the range of thousands are easily reached even by assuming minimal quantities.17,24,30

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b02170.

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Typical procedures, characterization data for all the compounds and E-factor calculations (PDF)

AUTHOR INFORMATION

Corresponding Author

*Luigi Vaccaro. Fax: +39 075 5855560; Tel: +39 075 5855541; E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the Università degli Studi di Perugia and di Palermo for financial support. The authors acknowledge FNRS for supporting the project (EQ funding). We also thank the Fondazione Cassa di Risparmio di Terni e Narni for financial support. Mr. Adrien Comès (Erasmus visiting student from the University of Namur) is gratefully acknowledged for preliminary experiments. This work was also supported by the REU program of the National Science Foundation under award number DMR1262908.

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CONCLUSIONS In conclusion, in this study we have reported the advantages of the use of a thiazolidine-supported Pd catalyst (10 wt %) and polystyrene-supported piperazine in the Sonogashira crosscoupling reaction. Our reaction conditions allow to reduce the 7214


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(21) For an example from another research group, see: Modak, A.; Mondal, J.; Bhaumik, A. Pd-grafted periodic mesoporous organosilica: an efficient heterogeneous catalyst for Hiyama and Sonogashira couplings, and cyanation reactions. Green Chem. 2012, 14, 2840−2855. (22) Petrucci, C.; Cappelletti, M.; Piermatti, O.; Nocchetti, M.; Pica, M.; Pizzo, F.; Vaccaro, L. Immobilized palladium nanoparticles on potassium zirconium phosphate as an efficient recoverable heterogeneous catalyst for a clean Heck reaction in flow. J. Mol. Catal. A: Chem. 2015, 401, 27−34. (23) Alonzi, M.; Bracciale, M. P.; Broggi, A.; Lanari, D.; Marrocchi, A.; Santarelli, M. L.; Vaccaro, L. Synthesis and characterization of novel polystyrene-supported TBD catalysts and their use in the Michael addition for the synthesis of Warfarin and its analogues. J. Catal. 2014, 309, 260−267. (24) Bonollo, S.; Lanari, D.; Longo, J. M.; Vaccaro, L. E-factor minimized protocols for the polystyryl-BEMP catalyzed conjugate additions of various nucleophiles to α,β-unsaturated carbonyl compounds. Green Chem. 2012, 14, 164−169. (25) Bonollo, S.; Lanari, D.; Angelini, T.; Pizzo, F.; Marrocchi, A.; Vaccaro, L. J. Catal. Rasta resin as support for TBD in base-catalyzed organic processes. J. Catal. 2012, 285, 216−222. (26) Marrocchi, A.; Adriaensens, P.; Bartollini, E.; Barkakaty, B.; Carleer, R.; Chen, J.; Hensley, D. K.; Petrucci, C.; Tassi, M.; Vaccaro, L. Novel cross-linked polystyrenes with large space network as tailor-made catalyst supports for sustainable media. Eur. Polym. J. 2015, 73, 391− 401. (27) Zvagulis, A.; Bonollo, S.; Lanari, D.; Pizzo, F.; Vaccaro, L. 2-tertButylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2- diazaphosphorine Supported on Polystyrene (PS-BEMP) as an Efficient Recoverable and Reusable Catalyst for the Phenolysis of Epoxides under Solvent-Free Conditions. Adv. Synth. Catal. 2010, 352, 2489− 2496. (28) Castrica, L.; Fringuelli, F.; Gregoli, L.; Pizzo, F.; Vaccaro, L. Amberlite IRA900N3 as a New Catalyst for the Azidation of α,βUnsaturated Ketones under Solvent-Free Conditions. J. Org. Chem. 2006, 71, 9536−9539. (29) Gruttadauria, M.; Liotta, L. F.; Salvo, A. M. P.; Giacalone, F.; La Parola, V.; Aprile, C.; Noto, R. Multi-Layered, Covalently Supported Ionic Liquid Phase (mlc-SILP) as Highly Cross-Linked Support for Recyclable Palladium Catalysts for the Suzuki Reaction in Aqueous Medium. Adv. Synth. Catal. 2011, 353, 2119−2130. (30) Pavia, C.; Ballerini, E.; Bivona, L. A.; Giacalone, F.; Aprile, C.; Vaccaro, L.; Gruttadauria, M. Palladium Supported on Cross-Linked Imidazolium Network on Silica as Highly Sustainable Catalysts for the Suzuki Reaction under Flow Conditions. Adv. Synth. Catal. 2013, 355, 2007−2018. (31) Bivona, L. A.; Giacalone, F.; Vaccaro, L.; Aprile, C.; Gruttadauria, M. Cross-Linked Thiazolidine Network as Support for Palladium: A New Catalyst for Suzuki and Heck Reactions. ChemCatChem 2015, 7, 2526−2533. (32) Petrucci, C.; Strappaveccia, G.; Giacalone, F.; Gruttadauria, M.; Pizzo, F.; Vaccaro, L. An E-factor minimized protocol for a sustainable and efficient Heck reaction in flow. ACS Sustainable Chem. Eng. 2014, 2, 2813−2819. (33) Strappaveccia, G.; Luciani, L.; Bartollini, E.; Marrocchi, A.; Pizzo, F.; Vaccaro, L. γ-Valerolactone as an alternative biomass-derived medium for the Sonogashira reaction. Green Chem. 2015, 17, 1071− 1076. (34) Verma, A. K.; Jha, R. R.; Chaudhary, R.; Tiwari, R. K.; Danodia, A. K. 2-(1-Benzotriazolyl)pyridine: A Robust Bidentate Ligand for the Palladium-Catalyzed C-C (Suzuki, Heck, Fujiwara−Moritani, Sonogashira), C-N and C-S Coupling Reactions. Adv. Synth. Catal. 2013, 355, 421−438. (35) Allouch, F.; Vologdin, N. V.; Cattey, H.; Pirio, N.; Naoufal, D.; Kanj, A.; Smaliy, R. V.; Savateev, A.; Marchenko, A.; Hurieva, A.; Koidan, H.; Kostyuk, A. N.; Hierso, J.-C. Ferrocenyl (P,N)diphosphines incorporating pyrrolyl, imidazolyl or benzazaphospholyl moieties: Synthesis, coordination to group 10 metals and performances

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Sustainable Approach to Waste-Minimized Sonogashira Cross

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