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1. Photochemical synthesis of acetals utilizing Schreiner's thiourea as the catalyst

Author:
Kokotos, Christoforos G.,   et al.   ; Spiliopoulou, Nikoleta; Nikitas, Nikolaos F.;     Show all 3 Authors
Source:
Green chemistry 2020 v.22 no.11 pp. 3539-3545
ISSN:
1463-9270
Subject:
aldehydes; catalysts; green chemistry; lamps; organic chemistry; photochemistry; reaction mechanisms; thiourea
Abstract:
... Acetalization of aldehydes is an area of great importance in Organic Chemistry for both synthetic and biological puproses. Herein, we report a mild, inexpensive and green photochemical protocol, where Schreiner's thiourea (N,N′-bis[3,5-bis(trifluoromethyl)-phenyl]-thiourea) is utilized as the catalyst and cheap household lamps as the light source. A variety of aromatic and aliphatic aldehydes were ...
DOI:
10.1039/d0gc01135e

2. Photochemical oxidation of benzylic primary and secondary alcohols utilizing air as the oxidant

Author:
Kokotos, Christoforos G.,   et al.   ; Nikitas, Nikolaos F.; Tzaras, Dimitrios Ioannis; Triandafillidi, Ierasia;     Show all 4 Authors
Source:
Green chemistry 2020 v.22 no.2 pp. 471-477
ISSN:
1463-9270
Subject:
air; alcohols; aldehydes; green chemistry; ketones; lamps; oxidants; oxidation; oxygen; photocatalysts; photochemistry; reaction mechanisms; solar radiation
Abstract:
... A mild and green photochemical protocol for the oxidation of alcohols to aldehydes and ketones was developed. Utilizing thioxanthenone as the photocatalyst, molecular oxygen from air as the oxidant and cheap household lamps or sunlight as the light source, a variety of primary and secondary alcohols were converted into the corresponding aldehydes or ketones in low to excellent yields. The reaction ...
DOI:
10.1039/c9gc03000j

3. Synthesis of γ-Lactones Utilizing Ketoacids and Trimethylsulfoxonium Iodide

Author:
Kokotos, Christoforos G.,   et al.   ; Triandafillidi, Ierasia; Savvidou, Anatoli;     Show all 3 Authors
Source:
Organic letters 2019 v.21 no.14 pp. 5533-5537
ISSN:
1523-7052
Subject:
carbonyl compounds; chemical structure; epoxidation reactions; epoxides; lactones
Abstract:
... The Johnson–Corey–Chaykovsky epoxidation is one of the oldest methods for the synthesis of terminal epoxides from carbonyl compounds. Herein we present a simplified extension of the Johnson–Corey–Chaykovsky epoxidation, where ketoacids are employed as the substrates and commercially available trimethylsulfoxonium iodide is employed as the carbon-atom homologating reagent. A variety of lactones are ...
DOI:
10.1021/acs.orglett.9b01852

4. Photo-organocatalytic synthesis of acetals from aldehydes

Author:
Kokotos, Christoforos G.,   et al.   ; Nikitas, Nikolaos F.; Triandafillidi, Ierasia;     Show all 3 Authors
Source:
Green chemistry 2019 v.21 no.3 pp. 669-674
ISSN:
1463-9270
Subject:
aldehydes; green chemistry; lamps; photocatalysts; reaction mechanisms
Abstract:
... A mild and green photo-organocatalytic protocol for the highly efficient acetalization of aldehydes has been developed. Utilizing thioxanthenone as the photocatalyst and inexpensive household lamps as the light source, a variety of aromatic and aliphatic aldehydes have been converted into acyclic and cyclic acetals in high yields. The reaction mechanism was extensively studied. ...
DOI:
10.1039/c8gc03605e

5. Organocatalytic synthesis of polysubstituted tetrahydrofurans from alkenes

Author:
Kokotos, Christoforos G.,   et al.   ; Theodorou, Alexis;     Show all 2 Author
Source:
Green chemistry 2017 v.19 no.3 pp. 670-674
ISSN:
1463-9270
Subject:
alkenes; catalytic activity; green chemistry; hydrogen peroxide; oxidants; oxidation; tetrahydrofuran
Abstract:
... A novel, organocatalytic and environmentally friendly protocol for the synthesis of polysubstituted tetrahydrofurans from trivial starting materials has been described. By employing 2,2,2-trifluoroacetophenone-mediated oxidation, which utilizes H₂O₂ as a green oxidant, we introduce a sustainable procedure that embraces the principles of green chemistry for the production of substituted tetrahydrof ...
DOI:
10.1039/c6gc02580c

6. Green Organocatalytic Synthesis of Isoxazolines via a One-Pot Oxidation of Allyloximes

Author:
Kokotos, Christoforos G.,   et al.   ; Triandafillidi, Ierasia;     Show all 2 Author
Source:
Organic letters 2017 v.19 no.1 pp. 106-109
ISSN:
1523-7052
Subject:
catalytic activity; hydrogen peroxide; moieties; organic compounds; oxidants; oxidation
Abstract:
... A green, sustainable, organocatalytic, and efficient synthesis of isoxazolines from allyloximes was developed. A 2,2,2-trifluoroacetophenone-catalyzed oxidation of allyloximes, utilizing H₂O₂ as the green oxidant, was taken advantage of in order to introduce a cheap and environmentally friendly protocol for the synthesis of substituted isoxazolines. A variety of substitution patterns, both aromati ...
DOI:
10.1021/acs.orglett.6b03380

7. Photocatalytic Synthesis of γ-Lactones from Alkenes: High-Resolution Mass Spectrometry as a Tool To Study Photoredox Reactions

Author:
Kokotos, Christoforos G.,   et al.   ; Triandafillidi, Ierasia; Kokotou, Maroula G.;     Show all 3 Authors
Source:
Organic letters 2018 v.20 no.1 pp. 36-39
ISSN:
1523-7052
Subject:
alkenes; chemical structure; mass spectrometry; monitoring; photocatalysis; photocatalysts; protocols; redox reactions
Abstract:
... A mild photocatalytic manifold for the synthesis of γ-lactones has been developed. Utilizing Ru(bpy)₃Cl₂ as the photocatalyst, a cheap and reproducible synthetic protocol for γ-lactones has been introduced. Mechanistic studies revealed the successful monitoring of photocatalytic reactions and radical intermediates via high-resolution mass spectrometry. ...
DOI:
10.1021/acs.orglett.7b03256

8. Proline dipeptides containing fluorine moieties as oganocatalysts for the asymmetric aldol reaction

Author:
Kokotos, Christoforos G.,   et al.   ; Ahmetlli, Ardiol; Spiliopoulou, Nikoleta; Magi-Oikonomopoulou, Angeliki; Gerokonstantis, Dimitrios-Triantaffylos; Moutevelis-Minakakis, Panagiota;     Show all 6 Authors
Source:
Tetrahedron 2018 v.74 no.40 pp. 5987-5995
ISSN:
0040-4020
Subject:
aldehydes; aniline; chemical reactions; dipeptides; enantioselectivity; fluorine; ketones; moieties; organocatalysts; phenylalanine; proline
Abstract:
... A series of dipeptide analogues consisting of proline, phenylalanine and aniline- or phenol-fluorine derivatives were synthesized. Their catalytic ability was evaluated in the intermolecular asymmetric aldol reaction, both in organic and aqueous media. Aniline-fluorine derivatives proved to be superior and the best results were obtained, when 2-CF3 aniline was employed. A diverse substrate scope c ...
DOI:
10.1016/j.tet.2018.08.038

9. Combining prolinamides with 2-pyrrolidinone: Novel organocatalysts for the asymmetric aldol reaction

Author:
Kokotos, Christoforos G.,   et al.   ; Vlasserou, Ismini; Sfetsa, Maria; Gerokonstantis, Dimitrios-Triantafyllos; Moutevelis-Minakakis, Panagiota;     Show all 5 Authors
Source:
Tetrahedron 2018 v.74 no.19 pp. 2338-2349
ISSN:
0040-4020
Subject:
aldehydes; chemical reactions; chemical structure; enantioselectivity; ketones; peptides; petroleum
Abstract:
... Peptides and especially prolinamides have been identified as excellent organocatalysts for the aldol reaction. The combination of prolinamides with derivatives bearing the 2-pyrrolidinone scaffold, deriving from pyroglutamic acid, led to the identification of novel organocatalysts for the intermolecular asymmetric aldol reaction. The new hybrids were tested both in organic and aqueous media. Among ...
DOI:
10.1016/j.tet.2018.03.054

10. Organocatalytic oxidation of substituted anilines to azoxybenzenes and nitro compounds: mechanistic studies excluding the involvement of a dioxirane intermediate

Author:
Kokotos, Christoforos G.,   et al.   ; Voutyritsa, Errika; Theodorou, Alexis; Kokotou, Maroula G.;     Show all 4 Authors
Source:
Green chemistry 2017 v.19 no.5 pp. 1291-1298
ISSN:
1463-9270
Subject:
acetonitrile; catalysts; catalytic activity; green chemistry; hydrogen peroxide; mass spectrometry; moieties; nitro compounds; oxidation
Abstract:
... An organocatalytic and environmentally friendly approach for the selective oxidation of substituted anilines was developed. Utilizing a 2,2,2-trifluoroacetophenone-mediated oxidation process, substituted anilines can be transformed into azoxybenzenes, while a simple treatment with MeCN and H₂O₂ leads to the corresponding nitro compounds, providing user-friendly protocols that can be easily scaled ...
DOI:
10.1039/c6gc03174a

11. One-Pot Amide Bond Formation from Aldehydes and Amines via a Photoorganocatalytic Activation of Aldehydes

Author:
Kokotos, Christoforos G.,   et al.   ; Papadopoulos, Giorgos N.;     Show all 2 Author
Source:
Journal of organic chemistry 2016 v.81 no.16 pp. 7023-7028
ISSN:
1520-6904
Subject:
aldehydes; ambient temperature; amides; amines; anxiety; chemistry; drugs
Abstract:
... A mild, one-pot, and environmentally friendly synthesis of amides from aldehydes and amines is described. Initially, a photoorganocatalytic reaction of aldehydes with di-isopropyl azodicarboxylate leads to an intermediate carbonyl imide, which can react with a variety of amines to afford the desired amides. The initial visible light-mediated activation of a variety of monosubstituted or disubstitu ...
DOI:
10.1021/acs.joc.6b00488

12. An Asymmetric Michael Addition of α,α-Disubstituted Aldehydes to Maleimides Leading to a One-Pot Enantioselective Synthesis of Lactones Catalyzed by Amino Acids

Author:
Kokotos, Christoforos G.
Source:
Organic letters 2013 v.15 no.10 pp. 2406-2409
ISSN:
1523-7052
Subject:
aldehydes; aspartic acid; catalysts; chemical reactions; enantiomers; enantioselective synthesis; lactones; phenylalanine
Abstract:
... A cheap and fast construction of both enantiomers of substituted succinimides is reported. α- or β-amino acids, such as β-phenylalanine and α-tert-butyl aspartate, were found to be efficient organocatalysts for the reaction between α,α-disubstituted aldehydes and maleimides. Products containing contiguous quaternary-tertiary stereogenic centers are obtained in high to quantitative yields and excel ...
DOI:
10.1021/ol4008662

13. One-Pot Synthesis of Ureas from Boc-Protected Amines

Author:
Kokotos, Christoforos G.,   et al.   ; Spyropoulos, Constantinos;     Show all 2 Author
Source:
Journal of organic chemistry 2014 v.79 no.10 pp. 4477-4483
ISSN:
1520-6904
Subject:
amines; chemical reactions; chemical structure; organic chemistry; synthesis
Abstract:
... A practical one-pot synthesis of ureas is described. Boc-protected amines can be transformed into nonsymmetrical and symmetrical disubstituted and trisubstituted ureas utilizing 2-chloropyridine and trifluoromethanesulfonyl anhydride for the in situ generation of an isocyanate, which reacts with an amine. A variety of amines can be employed successfully, leading to high yields of isolated ureas. ...
DOI:
10.1021/jo500492x

14. 2,2,2-Trifluoroacetophenone: An Organocatalyst for an Environmentally Friendly Epoxidation of Alkenes

Author:
Kokotos, Christoforos G.,   et al.   ; Limnios, Dimitris;     Show all 2 Author
Source:
Journal of organic chemistry 2014 v.79 no.10 pp. 4270-4276
ISSN:
1520-6904
Subject:
alkenes; catalysts; chemical structure; epoxidation reactions; epoxides; hydrogen peroxide; ketones; organic chemistry; oxidants; oxidation
Abstract:
... A cheap, mild, fast, and environmentally friendly oxidation of olefins to the corresponding epoxides is reported using polyfluoroalkyl ketones as efficient organocatalysts. Namely, 2,2,2-trifluoroacetophenone was identified as an improved organocatalyst for the epoxidation of alkenes. Various olefins, mono-, di-, and trisubstituted, are epoxidized chemoselectively in high to quantitative yields ut ...
DOI:
10.1021/jo5003938

15. Enantioselective Organocatalytic Synthesis of 2-Oxopiperazines from Aldehydes: Identification of the Elusive Epoxy Lactone Intermediate

Author:
Kokotos, Christoforos G.,   et al.   ; Kaplaneris, Nikolaos; Spyropoulos, Constantinos; Kokotou, Maroula G.;     Show all 4 Authors
Source:
Organic letters 2016 v.18 no.22 pp. 5800-5803
ISSN:
1523-7052
Subject:
aldehydes; catalytic activity; chemical structure; chlorination; enantioselectivity; epoxides; oxidation; reaction mechanisms
Abstract:
... An organocatalytic linchpin catalysis approach was envisaged to convert simple aldehydes into enantioenriched 2-oxopiperazines. A four-step reaction sequence (chlorination, oxidation, substitution, and cyclization) was developed and led to different substitution patterns in high yields and selectivities. The reaction mechanism was studied, and the previously elusive epoxy lactone intermediate was ...
DOI:
10.1021/acs.orglett.6b02699

16. Photoorganocatalytic synthesis of lactones via a selective C–H activation–alkylation of alcohols

Author:
Kokotos, Christoforos G.,   et al.   ; Kaplaneris, Nikolaos; Bisticha, Aikaterini; Papadopoulos, Giorgos N.; Limnios, Dimitris;     Show all 5 Authors
Source:
Green chemistry 2017 v.19 no.18 pp. 4451-4456
ISSN:
1463-9270
Subject:
lactones; photocatalysis; carbon-hydrogen bond activation; organic chemistry; cyclization reactions; green chemistry; photocatalysts
Abstract:
... Selective C–H activation is an area of growing importance in modern organic chemistry. Herein, we report our efforts in combining organocatalysis and photocatalysis for the development of a highly efficient and selective visible-light mediated protocol for the C–H activation and addition of various alcohols to a plethora of Michael acceptors, followed by a cyclization reaction leading to lactones, ...
DOI:
10.1039/c7gc01903c

17. Visible-Light-Mediated Catalytic Hydroacylation of Dialkyl Azodicarboxylates by Graphite Flakes

Author:
Kokotos, Christoforos G.,   et al.   ; Koutoulogenis, Giorgos S.; Kokotou, Maroula G.; Voutyritsa, Errika; Limnios, Dimitris;     Show all 5 Authors
Source:
Organic letters 2017 v.19 no.7 pp. 1760-1763
ISSN:
1523-7052
Subject:
aldehydes; catalysts; catalytic activity; chemical reactions; graphene; moieties
Abstract:
... A novel and efficient metal-free catalyzed hydroacylation of dialkyl azodicarboxylates is reported. Graphite flakes were found to be the most efficient catalyst among other carbon-based materials to promote this reaction. This unprecedented catalytic activity can be expanded into a wide substrate scope of aliphatic aldehydes bearing various functional groups, leading to the corresponding products ...
DOI:
10.1021/acs.orglett.7b00519

18. Construction of Tertiary Alcohols Bearing Perfluoroalkyl Chains Catalyzed by Prolinamide-Thioureas

Author:
Kokotos, Christoforos G.
Source:
Journal of organic chemistry 2012 v.77 no.2 pp. 1131-1135
ISSN:
1520-6904
Subject:
acetone; alcohols; aspartic acid; catalysts; organic chemistry
Abstract:
... A systematic study to evaluate the ability of various organocatalysts to catalyze the aldol reaction between acetone and 2,2,2-trifluoromethyl-1-phenylethanone was undertaken. Benchmark organocatalysts failed to catalyzethis reaction. However, a prolinamide-thiourea consisting of (S)-prolinamide, (1S,2S)-diphenylethylenediamine, and (S)-di-tert butyl aspartate proved to be an efficient catalyst, p ...
DOI:
10.1021/jo2020104

19. Microwave-assisted organocatalytic cross-aldol condensation of aldehydes

Author:
Kokotos, Christoforos G.,   et al.   ; Limnios, Dimitris;     Show all 2 Author
Source:
RSC advances 2013 v.3 no.14 pp. 4496-4499
ISSN:
2046-2069
Subject:
Cyclamen; aldehydes; catalysts; catalytic activity; condensation reactions; microwave radiation; microwave treatment; solvents
Abstract:
... An environmentally benign organocatalytic cross-aldol condensation of aldehydes under microwave irradiation in the absence of solvent is described. Using pyrrolidine as a catalyst, an efficient and sustainable atom economic method was developed for the cross-aldol condensation of various aldehydes with excellent results. Among the products, jasmine aldehyde, α-hexyl cinnamaldehyde and cyclamen ald ...
DOI:
10.1039/c3ra00114h

20. 4-Fluoro and 4-Hydroxy Pyrrolidine-thioxotetrahydropyrimidinones: Organocatalysts for Green Asymmetric Transformations in Brine

Author:
Kokotos, Christoforos G.,   et al.   ; Kaplaneris, Nikolaos; Koutoulogenis, Giorgos; Raftopoulou, Marianna;     Show all 4 Authors
Source:
Journal of organic chemistry 2015 v.80 no.11 pp. 5464-5473
ISSN:
1520-6904
Subject:
catalysts; chromatography; fluorine; organic chemistry; solvents
Abstract:
... The synthesis of both trans- and cis-diastereomers of pyrrolidinine-thioxotetrahydropyrimidinone bearing either a fluorine or a hydroxyl group was accomplished. The new compounds were tested for their catalytic properties in a variety of asymmetric organic transformations and compared with the first generation catalyst. It was found that the new catalysts could efficiently catalyze the reactions i ...
DOI:
10.1021/acs.joc.5b00283