Synthesis of Beta Lactams and Products Obtained From Them: Comparison
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Discovery and synthesis of penicillin and other beta-lactam antibiotics have received sustained attention. The use of β-lactam antibiotics is extensively documented in several thousand of publications. In modern times, microwave-induced reactions are also used extensively for the synthesis and stereochemical studies of diverse β-lactams. In this paper, the author describes a few crucial reactions that are performed toward the synthesis of β-lactams and products obtained from them under classical conditions as well as by domestic or automated microwave oven.

  • Beta Lactam
  • Synthesis
  • Microwave
  • Stereochemistry
  • Environmentally Benign

Introduction

Since the discovery and synthesis of penicillin, numerous β-lactam antibiotics have received attention. The use of β-lactam antibiotics is extensively documented in several books [1]. In modern times, microwave-induced reactions have been used extensively for the synthesis of diverse β-lactams.  In this paper, the author describes some of the notable reactions that are performed toward the synthesis of β-lactams and products obtained from them under classical conditions as well as by domestic or automated microwave oven.

Results

We have been engaged in chemical and medicinal research on β-lactams for the past many years. This endeavor has become successful in the synthesis of diverse molecules. In particular, many of the products are prepared using domestic and automated microwave oven. A few reactions that are developed in our laboratory on β-lactams are mentioned in this perspective. To know these reactions in details, it is advised to go through the original references.

Synthesis of Racemic β-Lactams

Reaction of acid chloride (equivalent) with imine in the presence of a tertiary amine was performed. This method is called Staudinger cycloaddition reaction. A diverse range of acid chlorides and imines were studied for the preparation of β-lactams. In many instances, cycloaddition was successful and high yields of the products with defined stereochemistry were obtained [2].

These reactions were also conducted using chlorobenzene, DMF, dichloroethane or in the absence of any solvents in automated or domestic microwave oven. The temperature of the reaction was 50-900C. In some examples, cis and trans β-lactams were formed [3].

A wide range of acid chlorides or activated acids were used successfully. Acetoxyacetyl chloride, benzyloxyacetyl chloride, phthalimidoacetyl chloride, phenoxyacetyl chloride, crotonyl chloride, phenylthio acetyl chloride, and butyryl chloride were employed for this purpose. The imines (Schiff bases) were prepared from aliphatic and aromatic primary amines by the reaction with carbonyl compounds (aldehydes and ketones) using a dehydrating agent. The stereochemistry of the β-lactams formed depended on many factors. The composition of the imine, acid chloride, conditions of the experiment and irradiation time was the crucial factors in determining the configuration of the β-lactams.  The diastereoselectivity of the β-lactams was altered by changing the conditions of the experiments and adjusting the power of microwave [2][3].

Synthesis of Optically Active β-Lactams

Optically active β-lactams were synthesized following cycloaddition under classical and microwave irradiation method. It was also possible to control the product distribution by adjusting the conditions of the experiments. Some reactions were enantioselective. In some instances, an alteration of the absolute stereochemistry was not possible by changing the conditions of the experiments. The cycloaddition followed kinetically or thermodynamically-controlled pathway depending upon the structures of the starting materials and the conditions of the reaction [4].

Synthesis of Racemic and Optically Active Anticancer β-Lactams

Reaction of polyaromatic imines with acid chlorides produced trans β-lactams as the only products. However, conjugated polyaromatic imines preferred to form cis β-lactams. Microwave-induced reaction produced identical trans β-lactams. Trisubstituted polyaromatic imines produced a mixture of two isomeric products under microwave irradiation.  A few trans β-lactams with angular ring system demonstrated anticancer activities in vitro against numerous cancer cell lines [5][6].

Synthesis of Glycosylated β-Lactams

The 3-hydroxy group of racemic and optically active β-lactams was reacted with a number of glycals in the presence of catalytic amounts of iodine. This reaction proceeded stereospecifically and separable glycosides were obtained. Finally, optically active β-lactams in enantiomeric forms were obtained [7].  Bismuth salts were also effective in catalyzing this process. Some of these methods were also investigated under automated microwave oven.

Synthesis of Amino β-Lactams

The preparation of amino β-lactams was performed by the reaction of phthalimido β-lactams with methyl hydrazine. The same compound was prepared using a domestic or an automated microwave oven. An extremely fast deprotection of the phthalimido group was observed [8]. No ring rupture of the β-lactam system was detected.

Synthesis of Pyrrole-Substituted β-Lactams

Iodine-catalyzed condensation of β-lactams with 2,5-hexane dione and 2,5-dimethoxytetrahydrofuran under microwave-assisted reaction produced pyrrole-substituted  β-lactams.  Bismuth salts were also used successfully for this reaction. This procedure was performed with racemic and chiral substrates. A microwave-induced reaction of racemic 3-keto β-lactam with optically active hydroxyl proline derivatives in the presence of mild acidic reagents afforded optically active cis and trans pyrrole-substutued β-lactams [9].

Hydrogenolysis and Hydrogenation of β-Lactams

Microwave-induced hydrogenolysis of the 3-benzyloxy group to the hydroxy group was performed by catalytic transfer hydrogenation. A number of hydrogen donors (ammonium formate, sodium formate and hydrazine) in the presence of Pd/C or Raney nickel were able to induce this transformation. The alkene group was hydrogenated smoothly by this condition. In some examples, a cleavage of the N-C4 bond was occurred. Non-cyclic amides were formed through this bond breakage reaction in some examples. The presence of multicyclic aromatic rings inhibited the cleavage of the bond [10].

β-Lactams as Synthons

Microwave-induced reaction of substituted β-lactams was used for molecular rearrangements to heterocyclic compounds [10]. A nucleophilic attack to the ring followed by the rearrangement was responsible for the overall success of this process. The ring rearrangement was the only route due to the strain present in the β-lactam system [10]. A few multicyclic β-lactams were prepared by radical-mediated and azide-alkyne cyclization methods [11].

Advantages of Microwave-Induced Reactions

Heating with a mantle or oil bath heats the walls of the vessels by convection or conduction. The reactants require longer time to be activated. On the other hand, microwave irradiation raises the temperature spontaneously. Our research had identified several advantages of microwave-induced reactions [3].  This includes fast reactions, mild method, useful selectivity, less solvent, high yield of the products and environmentally benign processes.

Conclusions

Synthesis of diverse β-lactams and products derived from them has become extremely useful. The results obtained as described herein by domestic and automated microwave oven remain identical. Microwave-mediate reactions are completed within minutes instead of hours that are required for reactions under conventional methods.

Acknowledgments

Bimal Krishna Banik is grateful to NIH, NCI, Kleberg Foundation, Stevens Institute of Technology, University of Texas M. D. Anderson Cancer Center, University of Texas-Pan American, University of Texas Health Science Center at San Antonio, Community Health System of South Texas and Prince Mohammad Bin Fahd University for their support to his research.

References

  1. For synthetic and biological studies on β-lactams, see: (a) Banik, B. K., Ed. “Heterocyclic Scaffolds I. Top. Heterocycl. Chem., Springer, 2010, 22, 1-376; (b) Banik, B. K., Ed. “β-Lactams: Synthesis and Biological Evaluation”, Top. Heterocycl. Chem., Springer, 2012, 30, 1-226; (c) Banik, I.; Banik, B. K., “Microwave-Induced Chemical Manipulation of β-Lactam”, Springer; 2012, 55, 751-1007; (d) Banik, B. K., Ed. “Beta Lactams: Novel Synthetic Pathways and Applications”, Springer, 2017, 1-416; (e) Parvatkar, P. T.; Parameswaran, P. S.; Banik, B. K., “Solid Phase Synthesis of β-Lactams: Results and Scope in Banik, B. K., Beta Lactams: Novel Synthetic Pathways and Applications, Ed. Spinger, 2017, 253-254; (f) Basu, S.; Banik, B. K., “Beta Lactams as Clinically Active Molecules” in Banik, B. K., Beta Lactams: Novel Synthetic Pathways and Applications, Ed. Springer, 2017, 255-310; (g) Banik, B. K., “Synthesis and Biological Studies of Novel β-Lactams”, CRC Book, 2013, 31-72.
  2. For the synthesis of racemic beta lactams by classical method, see: (a) Bose, A. K.; Banik, B. K.; Newaz, S. N.; Manhas, M. S., “Vinyl β-Lactams: Convenient Elaboration of the Thienamycin Side Chain”, Synlett, 1993, 897-899; (b) Ghatak, A.; Becker, F. F.; Banik, B. K., “Synthesis of 3-Unsubstitiuted Ferrocenyl β-Lactams by Indium Induced Reaction”, Heterocycles 2000, 53, 2769-2773; (c) Banik B. K.; Ghatak A.; Becker, F. F., “Indium-Mediated Synthesis of 3-Unsubstituted β-Lactams”, J. Chem. Soc., Perkin Trans 1, 2000, 2179-2181; (d) Dasguptam S. K.; Banik B. K., “New Entry to N-Unsubstituted β-Lactams Under Solid-Support”, Tetrahedron Lett., 2002, 43, 9445-9447; (e) Banik, I.; Yadav, R. N.; Becker, F. F.; Banik, B. K., “Stereospecifc Beta-Lactam Formation via Staudinger Cycloaddition Derived From Ferrocenyl Imines”, J. Indian Chem. Soc., 2018, 95, 833-836.
  3. For the synthesis of beta lactams by microwave-induced methods, see: (a) Bose, A. K.; Manhas, M. S.; Ghosh, M.; Shah, M.; Raju, V. S.; Bari, S. S.; Newaz, S. N.; Banik, B. K.; Barakat, K. J.; Chaudhury, A. G., “Microwave-Induced Organic Reaction Enhancement Chemistry. 2. Simplified Techniques”; J. Org. Chem., 1991, 56, 6968-6970; (b) Banik, B. K.; Manhas, M. S.; Newaz, S. N.; Bose, A. K., “Facile Preparation of Carbapenem Synthons via Microwave-Induced Rapid Reaction”; Bioorg. & Med. Chem. Lett., 1993, 3, 2363-2368; (c) Banik, B. K.; Manhas, M. S.; Newaz, S. N.; Bose, A. K., “Facile Preparation of Carbapenem Synthons via Microwave-Induced Rapid Reaction”, Bioorg. & Med. Chem. Lett., 1993, 3, 2363-2368; (d) Bose, A. K.; Banik, B. K.; Barakat, K. J.; Manhas, M. S., "Simplified Rapid Hydrogenation Under Microwave Irradiation: Selective Transformations of β-Lactams", Synlet, 1993, 8, 575-576; (e) Bose, A. K.; Manhas, M. S.; Banik, B. K.; Robb, E. W., “Microwave-Induced Organic Reaction Enhancement (MORE) Chemistry: Techniques for Rapid, Safe and Inexpensive Synthesis”; Res. Chem. Interm., 1994, 20, 1-11; (f) Bose, A. K.; Banik, B. K; M. S. Manhas, "Stereocontrol of β-Lactam Formation Using Microwave Irradiation", Tetrahedron Lett., 1995, 36, 213-216; (g) Banik, B. K.; Jayaraman, M.; Srirajan, V.; Manhas, M. S.; Bose, A. K. “Rapid Synthesis of β-Lactams as Intermediates for Natural Products via Eco-friendly Reactions”, J. Ind. Chem. Soc., 1997, 74, 943-947; (h) Banik, B. K.; Manhas, M. S.; Robb, E. W.; Bose, A. K., "Environmentally Benign Chemistry: Microwave-Induced Stereocontrolled Synthesis of β-lactam Synthons", Heterocycles 1997, 44, 405-415; (i) Manhas, M. S.; Banik, B. K.; Mathur, A.; Vincent, J.; Bose, A. K, “Microwave-Assisted Synthesis of Vinyl β-Lactam: Synthons for Natural Products”, Tetrahedron, 2000, 56, 5587-5601; (j) Ramos, K.; Banik, B. K., “Microwave-Induced Clay-Mediated Preparation of Imines: One-Pot Synthesis of β-Lactams”, Heterocyclic Letters, 2011, 27-30; (k) Banik, I.; Yadav, R. N.; Banik, B. K., “Microwave-Induced Synthesis of Bis β-Lactams from Hydrazides”, 2018, Asian J. Org. & Med. Chem., DOI: https://doi.org/10.14233/ajomc.2018.AJOMC-P83; (l) Banik, I.; Yadav, R. N.; Banik B. K., “Stereoselective Synthesis of Trans Acetoxy -Lactams Under Microwave Irradiation”, J. Ind. Chem. Soc., 2018, 95, 1405-1407; (m) Yadav, R. N.; Chavez, A.; Banik, B. K., “Microwave-Induced Cycloaddition of Imines with Acid Chlorides in the Absence of a Tertiary Amine: Unprecedented Synthesis of -Lactams in Dimethylformamide”, J. Ind. Chem. Soc., 2018, 95, 1365-1367; (n) Yadav, R. N.; Banik, I.; Banik, B. K. “Stereoselective Synthesis of Trans Acetoxy -Lactams Under Microwave Irradiation”, J. Ind. Chem. Soc., 2018, 95, 1405-1407; (o) Yadav, R. N.; Banik, I.; Banik, B. K., “Optically Active 4-Formyl -Lactams: Microwave-Induced Deacetonation-Oxidation”, J. Ind. Chem. Soc., 2018, 95, 1389-1391; (p) Yadav, R. N.; Banik, I.; Banik, B. K., “Microwave-Mediated Synthesis of 3-Unsubstituted β-Lactams with Aqueous Trimethylborane”, J. Ind. Chem. Soc., 2018, 95, 1381-1384; (q) Yadav, R. N.; Banik, I.; Banik, B. K. “Microwave-Induced New Synthesis of Trans and Cis-3-Phenylthio-4-Carboethoxy -Lactams”, J. Ind. Chem. Soc., 2019, 96, 1355-1358; (r) Yadav, R. N.; Banik, I.; Banik, B. K. “Microwave-Induced New Synthesis of Trans 3-Phenylthio-4-Carboethoxy -Lactams”, J. Ind. Chem. Soc., 2019, 96, 1359-1362.
  4. For the synthesis of chiral beta lactams, see: (a) Banik, B. K.; Manhas, M. S.; Kaluza, Z.; Barakat, K. J.; Bose, A. K.; “Microwave-Induced Organic Reaction Enhancement Chemistry. 4 Convenient Synthesis of Enantiopure α-Hydroxy-β-Lactams”, Tetrahedron Lett., 1992, 33, 3603-3606; (b) Banik, I.; Okawa, A.; Banik, B. K.; “Synthesis of Racemic and Optically Active β-Lactams Derived from Allyl and Propargyl Imine”, Heterocyclic Letters 2011, 83-85; (c) Solano Fonseca, R.; Mukherjee, S.; Banik, B. K.; “Asymmetric Synthesis of β-Lactam Using S-Citranellal”, Heterocyclic Lett., 2011, 97-98; (d) Nambiar, A.; Rodriguez, R.; Yadav, R. N.; Banik, B. K. “Synthesis of Novel C-4 Disubstituted β-Lactam that have Pyrrole”, Heterocyclic Lett., 2014, 4, 417-419; (e) Chandra, S.; Yadav, R. N.; Lareeb, L.; Banik, B. K. “Synthesis of 3-Unsubstituted β-Lactams Using Radical Reactions”, Chem. Edu., 2015, 20, 4-5; (f) Banik, I.; Becker, F. F.; Banik, B. K., “Microwave-Induced Synthesis of Enantiopure β-Lactams”, Modern Chem. & Applications, 2017, 5:3. DOI: 10.4172/2329-6798.1000228; (g) Yadav, R. N.; Banik, I.; Banik, B. K.; “Microwave-Induced Synthesis of Enantiopure Beta Lactams form L-Glyceraldehyde”, J. Ind. Chem. Soc., 2018, 95, 1393-1395; (h) A. Shaikh; Yadav, R. N.; Banik, B. K.; “Asymmetric Synthesis of β-Lactams from Natural Carene”, 2020, Rus. J. Chem., in press.
  5. Banik, B. K.; Becker, F. F., “Unprecedented Stereoselectivity in the Staudinger Reaction with Polycyclic Aromatic Imines”, Tetrahedron Lett., 2000, 41, 6551; (b) I. Banik, I.; Hackfeld, L.; Banik, B. K., “Cycloaddition of with Naphthalenyl and Anthracenyl Imines: Interesting Aspects of the Staudinger Reaction”, Heterocycles, 2003, 59, 505-508; (c) Banik, B. K.; Aguilar, H., Cordova, D., “Unprecedented Stereocontrol of β-Lactam Formation Derived From N-Cinnamylidenearylamine”, Heterocycles, 2007, 71, 2321-2324; (d) Aguilar, H.; Banik, B. K., “Stereoselctivity of 3,3-Disubstituted β-Lactam Formation Via Staudinger Reaction”, Heterocyclic Communications, 2009, 15, 365-368; (e) Bandyopadhyay, D.; Xavier, M; Banik, B. K., “Highly Stereoselective Beta-Lactam Synthesis via the Staudinger Reaction Using Polyaromatic Imines”, Heterocyclic Communications 2009, 15, 229-232; (f) Bandyopadhyay, D.; Banik, B. K., “Microwave-Induced Stereoselectivity of β-Lactam Formation with Dihydrophenanthrenyl Imines via Staudinger Reaction”, Helv. Chim. Acta., 2010, 93, 298-301; (g) Rodriguez, R.; Banik, B. K., “Unprecedented Stereoselectivity of β-Lactam Formation via Staudinger Reaction with Conjugated Imines Derived from Polyaromatic Systems”, Heterocyclic Lett., 2011, 31-34; (h) Shaikh, A. L.; Esparza, O.; Banik, B. K., “An Efficient Synthesis of Optically Active Trans (3R,4R)-N-(Chrysenyl)-3-Acetoxy-4-Aryl-2-Azatidinones Using Caryene as a Chiral Auxiliary”, Helv. Chim. Acta., 2011, 94, 2188-2193; (i) Banik, I.; Samajdar, S.; Banik, B. K., “Microwave-Induced Stereospecific Synthesis of β-Lactams Derived from Polyaromatic Imines: Influence of Multicyclic Rings at the Nitrogen”, Heterocyclic Lett., 2011, 55-57; (j) Bandyopadhyay, D.; Yanez, M.; Banik, B. K., “Microwave-Induced Stereoselectivity of β-Lactam Formation: Effects of Solvents”, Heterocyclic Lett., 2011, 65-67; (k) Banik, I.; Becker, F. F.; Banik, B. K., “Stereoselective Synthesis of β-Lactams Derived from Chrysenyl Imine”, Heterocyclic Lett., 2011, 79-81; (l) Yadav, R. N.; Banik, I.; Banik, B. K., “Microwave-Assisted Novel Stereoselective Synthesis of Bis-β-Lactams with 2,7-Phenanthrenyl Imines”, J. Ind. Chem. Soc., 2018, 95, 1377-1380; (m) Yadav, R. N; Marquez, J.; Srivastava, A. K.; Singh, A.; Banik, B. K., “Novel Synthesis of Bis β-Lactams With Unsual 2,7-Phenanthrene and 9,10-Dihydrophenanthrene”, Asian J. Org. Med. Chem., 2018, DOI: https://doi.org/10.14233/ajomc.2018.AJOMC-P110.
  6. Banik, I.; Becker, F. F.; Banik, B. K., “Stereoselective Synthesis of β-Lactams with Polyaromaic Imines: Entry to New and Novel Anticancer Agents”, J. Med. Chem. 2003, 46, 12-15; (b) Banik, B. K., Becker, F. F.; Banik, I., “Synthesis of Anticancer β-Lactams: Mechanism of Action”, Bioorg. Med. Chem., 2004, 12, 2523-2528; (c) Banik, B. K.; Banik, I.; Becker, F. F., “Stereocontrolled Synthesis of Anticancer β-Lactams via the Staudinger Reaction”, Bioorg. Med. Chem. 2005, 13, 3611-3622; (d) Banik, B. K.; Lecea, B.; Arrieta, A.; Cozar, A,; Cossio, F. P., “On the Stereodivergent Behavior Observed in the Staudinger Reaction Between Methoxyketene and (E)-N-Arylbenzylidenearyl Amines”, Angew. Chem. Int. Ed., 2007, 46, 3028-3032; (e) Banik, B. K.; Aguilar, H.; Cordova, D.; “Unprecedented Stereocontrol of β-Lactam Formation Derived From N-Cinnamylidene Arylamine”, Heterocycles, 2008, 11, 2321-2329; (f) Banik, I.; Becker, F. F.; Banik, B. K., “Selective Anticancer Activity of β-Lactams Derived From Polyaromatic Compounds”, Molecular Medicine Reports, 2010, 3, 315-316; (g) Banik, B. K.; Samajdar, S.; Becker, F. F., “Asymmetric Synthesis of Anticancer β-Lactams Via Staudinger Reaction”, Molecular Medicine Reports, 2010, 3, 319-321; (h) Banik, I. Banik; Becker, F. F.; Banik, B. K., “Asymmetric Synthesis of Anticancer β-Lactams via Staudinger Reaction: Utilization of Chiral Ketene from Carbohydrate”, Eur. J. Med. Chem., 2010, 45, 846-848; (i) H. Mohamed, H.; Banik, B. K., “Synthesis of Vinyl β-Lactams: Insights on the Mechanism of Their Formation”, Heterocyclic Lett., 2011, 23-26; (j) Banik, I.; Becker, F. F.; Banik, B. K.; Microwave-Induced Stereospecific Synthesis of β-Lactams Derived from Polyaromatic Imines: Influence of Multicyclic Rings at the Nitrogen, Heterocyclic Lett., 2011, 55-57; (k) Bandyopadhyay, D.; Yanez, M. A.; Banik, B. K.; Microwave-Induced Stereoselectivity of β-Lactam Formation, Effects of Solvents; Heterocyclic Lett., 2011, 65-67; (l) Banik, B. K. “Anticancer β-Lactams and Related Investigations: Synthesis and Biological Evaluation”, J. Ind. Chem. Soc., 2014, 91, 1837-1860.
  7. Banik, B. K.; Manhas, M. S.; A. K. Bose, "Stereospecific Glycosylation via Ferrier Rearrangement for Optical Resolution", J. Org. Chem., 1994, 59, 4714-4716; (b) Banik, B. K.; Manhas, M. S.; Bose, A. K., "Enantiopure Hydroxy β-Lactams via Glycosylation", Tetrahedron Lett., 1997, 38, 5077-5080; (c) Banik, B. K.; Zegrocka, O.; Manhas, M. S.; Bose, A. K., “Enantiomerically Pure β-Lactams with the Thienamycin Side Chain via Glycosylation”, Heterocycles, 1997, 46, 173-176; (d) Banik, B. K.; Zegrocka, O.; Manhas, M. S.; Bose, A. K., “A Facile Iodine-Catalyzed Stereospecific Glycosylation: Enantiomerically Pure β-Lactams with the Thienamycin Side Chain”, Heterocycles, 2009, 78, 2443-2454; (e) Banik, B. K.; Manhas, M. S., “Iodine-Catalyzed Stereospecific Glycosylation of Alcohols: Enantiopure β-Lactams”, Tetrahedron 2012, 68, 10769-10779; (f) Banik, I.; Becker, F. F.; Banik, B. K., “Microwave-Mediated Chiral Synthesis of O-Glycosides of β-Lactams”, Asian J. Org. & Med. Chem., 2018, i DOI: https://doi.org/10.14233/ajomc.2018.AJOMC-P81; (g) Banik, I.; Yadav, R. N; Becker, F. F.; Banik, B. K., “Bismuth Nitrate-Induced Microwave-Mediated Deglycosylation of O-Glycosides: Synthesis of Enantiopure 3-Hydroxy β-Lactams”, J. Ind. Chem. Soc., 2018, 95, 1373-1376.
  8. Bandyopadhyay, D.; Sanchez Rivera, G.; Salinas, I.; Aguilar, H.; Banik, B. K., “Remarkable Iodine-Catalyzed Synthesis of Novel Pyrrole-Bearing N-Polyaromatic β-Lactams”, Molecules, 2010, 15, 1082-1088; (b) Bandyopadhyay, D.; Mukherjee, S.; Banik, B. K., “An Expeditious Synthesis of N-Substituted Pyrroles by Microwave-induced Iodine-Catalyzed Reactions Under Solventless Conditions”, Molecules, 2010, 15, 2520-2525; (c) Shaikh, A.; Banik, B. K., “A Novel Asymmetric Synthesis of 3-Pyrrole Substituted β-Lactams Via Bismuth Nitrate-Catalyzed Reaction”, Helv. Chim. Acta., 2012, 95, 839-844; (d) Bandyopadhyay, D.; Cruz, J.; Banik, B. K., Microwave-Induced Synthesis of 3-Pyrrole Substituted β-Lactams Via Bismuth Nitrate-Catalyzed Reaction, Tetrahedron Symposium-in-Print, 2012, 68, 10686-10695; (e) Bandyopadhyay, D.; Cruz, J.; Yadav, R. N.; Banik, B. K., “An Expeditious Iodine-Catalyzed Synthesis of 3-Pyrrole Substituted 2-Azetidinones”, Molecules, 2012, 17, 11570-11584; (f ) Shaikh, A.; Banik, B. K., “Novel Asymmetric Synthesis of 3-Pyrrole-Substituted β-Lactams Through Bismuth Nitrate-Catalyzed Reaction”, SOAJ Org. Biomol. Chem., 01, ID 010301, 2013; (g) Bandyopadhyay, D.; Rhodes, E.; Banik, B. K., “A Green, Chemoselective, and Practical Approach Toward N-(2-azetidinonyl)-2,5-disubstituted Pyrroles”, Royal Society Advance, 2013, 3, 16756-16764.
  9. (a) Paniagua, A.; Yadav, R. N.; Chandra, S.; Banik, B. K., “Synthesis of 3-Amino Beta Lactams Through Facile Deprotection of 3-Phthalimido Group”, Heterocycles Lett., 2018, 8, 287-295; (b) I. Banik, I.; Yadav, R. N.; Bose, A. K.; Banik, B. K., “Acetylation of the Amino Group in β-Lactams Under Aqueous Conditions: Effects of Ring Sizes”, J. Ind. Chem. Soc., 2019, 96, 1343-1346; (c) Yadav, R. N.; Srivastava, A.; Banik, B. K., “Microwave-Induced Bismuth Nitrate-Catalyzed Michael Reaction of 3-Amino Beta-Lactams with Enones”, Asian J. Chem., 2020, 32, 233-236.
  10. (a) Banik, B. K.; Manhas, M. S.; Bose, A. K., "Versatile β-Lactam Synthons: Enantiospecific Synthesis of (-)-Polyoxamic acid", J. Org. Chem.,1993, 58, 307-309; (b) Bose, A. K.; Banik, B. K.; Mathur, C.; Wagle, D. R.; Manhas, M. S., "Polyhydroxy Amino Acid derivatives via β-Lactams Using Enantiospecific Approaches and Microwave Techniques”, Tetrahedron, 2000, 56, 5603-5619; (c) Banik, B. K.; Barakat, K.; Wagle, D. R.; Manhas, M. S.; Bose, A. K., “Microwave Assisted Rapid and Simplified Hydrogenation”, J. Org. Chem., 1999, 64, 5746-5753; (d) Banik, B. K.; Samajdar, S.; Banik, I., “Indium-Induced Facile Rearrangement of β-Lactams to Oxazines”, Tetrahedron Lett., 2003, 44, 1699-1701; (e) Yadav, R. N.; Newaz, S. N.; Bose, A. K.; Banik, B. K., “Studies on Substituted Beta Lactams Towards Ring Opening: Elimination Versus Rearrangement”, Modern Chemistry & Applications, 2018, 6:2; DOI: 10.4172/2329-6798.1000254; (f) Yadav, R. N.; Banik, I.; Banik, B. K., “Synthesis of Optically Active Lactones Through Ring Opening of Beta Lactams Under Microwave Conditions”, J. Ind. Chem. Soc., 2018, 1401-1403.
  11. (a) Banik, B. K.; Subbaraju, G. V.; Manhasm M. S.; Bose, A. K., "Fused Tricyclic β-Lactams via Intramolecular Aryl Radical Cyclization", Tetrahedron Lett., 1996, 37, 1363-1366; (b) Ng, S.; Banik, I.; Okawa, A.; Becker, F. F.; Banik, B. K., “Synthesis of Tricyclic β-Lactams via Palladium Acetate Mediated Heck Reaction”, J. Chem. Res., 2001, 118-119; (c) Yadav, R. N.; Chandra, S.; Banik, B. K., “Metal-Free Azide-Alkyne Cycloaddition: Synthesis of Polycyclic -Lactams”, Aust. J. Chem., 2020, in press.
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