The laccase-catalyzed reaction between unsubstituted catechol and 2-thioxopyrimidin-4(1H)-ones using aerial O2 as the oxidant delivers novel pyrimidobenzothiazoles with high yields in an aqueous solvent system under mild reaction conditions. With 4-substituted catechols, catechol thioethers are formed exclusively. The synthetic protocols developed provide a sustainable approach for these compound classes. In addition, the cytotoxicity of the products against HepG2 cell line is reported. Most compounds exhibit antiproliferative activities with IC50 values at the micromolar level. A structure–activity relationship study will facilitate the further development of these compounds as cytotoxic agents.

Substrates bearing both a β-ketoester moiety and a (het)aryl halide structure element were dimerized to 1-naphthols and related products in the presence of catalytic amounts of CuI in isopropanol. The reaction starts with an intermolecular C-arylation, which is followed by an intramolecular condensation. The final aromatization delivers the highly substituted products with yields up to 81%.

The three-component reaction between a nitrobenzene, an aldehyde, and a dienophile in the presence of iron powder as a reductant and montmorillonite K10 as a catalyst in aqueous citric acid delivers the products of an aza-Diels–Alder (Povarov) reaction with high endo-selectivity and yields up to 99%.

The reaction of 5-substituted 2-nitrosophenols with bromomethyl aryl ketones and related compounds employing K2CO3 as a base in refluxing THF and DMF at 80 °C, respectively, delivers 2-aroylbenzoxazoles in a single step with yields up to 85%. The new method involves an intermolecular nucleophilic substitution followed by intramolecular 1,2-addition and elimination. It allows an efficient and practical access to 2-aroylbenzoxazoles under transition-metal-free conditions.

•Development of new temperature sensitive paints (TSPs) based on new Eu complexes.•TSPs have exceptional high T sensitivities and negligible p sensitivities.•TSPs are suitable for luminescence intensity and luminescence lifetime measurements.•TSPs can be used over a wide T range.•Practical application in aerodynamics as well as hydrodynamics.The synthesis of novel Eu complexes with 1,3-di(thienyl)propane-1,3-diones as ligands as well as their luminescence properties in different polymers are reported. The new temperature sensitive paints (TSPs) exhibit not only exceptional high temperature sensitivity over a wide range of temperatures but are also characterized by negligible pressure sensitivity and marked photostability. This is why they are outstandingly suitable for applications, e.g. in aerodynamics and hydrodynamics.

The laccase-catalyzed reaction between catechols and thiols using aerial oxygen as the oxidant delivers the corresponding catechol thioethers with yields up to 96% under mild reaction conditions.

The Cu(I)-catalyzed reaction of 2,3-dibromo-1-propenes with β-ketoesters and 1,3-diketones, respectively, in DMF at 120 °C using Cs2CO3 as a base and hydroquinone as an additive exclusively delivers 2,3,5-trisubstituted furans and related compounds with yields up to 96%. The highly regioselective domino process is based on an intermolecular C-allylation followed by an intramolecular Ullmann type O-vinylation and a double bond isomerization.

A transition-metal-free route for the synthesis of several N-fused heterocycles, including thiazolo[3,2-a]benzimidazoles and imidazo[2,1-b]thiazoles, is reported. The reaction between propargyl tosylates and 2-mercaptobenzimidazoles under basic conditions results in 3-substituted thiazolo[3,2-a]benzimidazoles, in yields up to 92% in a single synthesis step. With 2-mercaptoimidazoles as the substrate, the corresponding imidazo[2,1-b]thiazoles were exclusively obtained. The transformation is considered to proceed as an intermolecular S-propargylation that is followed by 5-exo-dig ring closure and double-bond isomerization.

A new method employing a laccase–mediator system as the catalyst and aerial oxygen as the oxidant has been developed for the oxidative coupling of heterocyclic thiols to the corresponding disulfides with yields up to 95% under mild reaction conditions.

The Lewis acid-catalyzed domino 1,2-addition/1,4-addition/elimination between (Z)-3-hexene-2,5-dione and 1,3-dicarbonyls delivers 3-methyl-6,7-dihydrobenzofuran-4(5H)-ones exclusively with yields up to 82%. The combination of this new process with the laccase-catalyzed formation of (Z)-3-hexene-2,5-dione by oxidative cleavage of 2,5-dimethylfuran allows for the synthesis of 6,7-dihydrobenzofuran-4(5H)-ones starting directly from 2,5-dimethylfuran.

The laccase-catalyzed oxidation of (5-alkylfuran-2-yl)carbinols using aerial oxygen as an oxidant selectively affords 6-hydroxy-(2H)-pyran-3(6H)-ones with yields up to 90%. With suitable substituted furan-2-yl carbinols as substrates the procedure allows the efficient preparation of (2H)-pyran-2,5(6H)-diones in a single step.

The reaction of 2-(bromomethyl)benzaldehydes with arylhydrazines employing K2CO3 as a base and FeCl3 as a catalyst in CH3CN at 100 °C delivers 2-aryl-1,2-dihydrophthalazines with yields ranging from 60 to 91%. The transformation is considered to proceed as an intermolecular condensation/intramolecular nucleophilic substitution.

Reactions between 1-nitroso-2-naphthols and α-functionalized ketones such as α-bromo-, α-chloro-, α-mesyloxy-, α-tosyloxy-, and α-hydroxy ketones under basic conditions delivered 2-substituted naphtho[1,2-d][1,3]oxazoles in a single synthetic operation. The product formation was accompanied by the unexpected loss of the C═O group from the α-functionalized ketones. With aryl bromides, allyl bromides, α-bromo diketones, α-bromo cyanides, α-bromoesters, and α-bromo ketoesters as substrates the formation of naphtho[1,2-d][1,3]oxazoles was also observed. The transformations were performed in 1,2-dichloroethane or acetonitrile under reflux and gave the corresponding naphthoxazoles with yields ranging between 52% and 85%.

The laccase-catalyzed domino reaction between catechols and 6-substituted 1,2,3,4-tetrahydro-4-oxo-2-thioxo-5-pyrimidinecarbonitriles using aerial O2 as the oxidant delivers new pyrimidobenzothiazole derivatives. The complete structure elucidation of the ring-proton deficient heterocyclic products and the unambiguous determination of the regioselectivity of the reactions have been achieved by extended NMR spectroscopic methods including HSQMBC, super long-range HMBC, and 15N measurements.

The laccase-catalyzed oxidative phenolic coupling of vanillidene derivatives using aerial oxygen as the oxidant has been developed. Depending on the substitution pattern of the vanillidene double bond of the substrate, either dilactones, dihydrobenzo[b]furans or biphenyls are formed.

The laccase-catalyzed oxidation of 1,4-dihydropyridines to pyridines using aerial O2 as the oxidant exclusively delivers pyridines with yields up to 95% under mild reaction conditions. Combination of the Hantzsch 1,4-dihydropyridine synthesis with the newly developed laccase-catalyzed oxidation forms the basis of a facile and environmentally benign method for the synthesis of pyridines in one pot.

Cu(I)-catalyzed reaction of o-bromobenzaldehydes with β-ketoesters using Cs2CO3 as a base and 2-picolinic acid as an additive proceeds under mild conditions and gives access to substituted naphthalenes in a single step with yields ranging from 71 to 86%. The new annulation process relies on a domino Knoevenagel condensation/C-arylation/1,2-addition/carboxylic acid cleavage. The annulation can also be achieved with o-iodobenzaldehyde.

The laccase-catalyzed oxidative coupling of sesamol, a naturally occurring phenolic antioxidant, with O2 as the oxidant proceeds with high selectivity and delivers a previously unknown trimer in 61% yield. Further experiments demonstrate that the outcome of the sesamol oxidation strongly depends on the catalyst and the oxidant employed.

As little as 0.5 mol % CuCl is sufficient to catalyze the intramolecular O-arylation of easily accessible 2-(2-bromobenzyl)cyclohexane-1,3-diones to provide the corresponding 2,3,4,9-tetrahydro-1H-xanthen-1-ones with yields ranging from 83% to 99%.

The Cu(I)-catalyzed reaction of 1-bromo-2-iodobenzenes and other 1,2-dihalobenzenes with 1,3-cyclohexanediones in DMF at 130 °C using Cs2CO3 as a base and pivalic acid as an additive selectively delivers 3,4-dihydrodibenzo[b,d]furan-1(2H)-ones with yields ranging from 47 to 83%. The highly regioselective domino process is based on an intermolecular Ullmann-type C-arylation followed by an intramolecular Ullmann-type O-arylation. Substituted products are accessible by employing substituted 1-bromo-2-iodobenzenes and substituted 1,3-cyclohexanediones as substrates. Reaction with an acyclic 1,3-diketone yields the corresponding benzo[b]furan.

Highly substituted p-benzoquinones were obtained in yields ranging from 39% to 98% by laccase-catalyzed domino reactions between hydroquinones and cyclic 1,3-dicarbonyls using aerial oxygen as the oxidant. In almost all reactions bis-adducts with two adjacent 1,3-dicarbonyl substituents on the quinone moiety were formed selectively. The transformations can be regarded as domino oxidation/1,4-addition/oxidation/1,4-addition/oxidation processes. With unsubstituted hydroquinone as the substrate 2,3-disubstituted p-benzoquinones were isolated. Bis-adducts were also formed exclusively upon reaction with monosubstituted hydroquinones. In almost all cases the 2,3,5-trisubstituted p-benzoquinones were obtained. When 2,3-disubstituted hydroquinones were employed as starting materials the 2,3,5,6-tetrasubstitutedp-benzoquinones were isolated. The unambiguous structure elucidation of all products has been achieved by NMR spectroscopic methods including spin pattern analysis of the long-range coupled C═O carbons and 13C satellites analysis in 1H NMR spectra.

The oxidative dimerization of 2-propenylsesamol to carpanone with O2 as the oxidant, which probably proceeds as a domino phenol oxidation/anti-β,β-radical coupling/intramolecular hetero Diels–Alder reaction, can be efficiently catalyzed by laccases. Experiments with laccases and other catalysts like a Co(salen) type catalyst and PdCl2 clearly demonstrate that the diastereoselectivity of the carpanone formation does not depend on the catalyst but on the double-bond geometry of the substrate. With (E)-2-propenylsesamol as the substrate, carpanone and a so far unknown carpanone diastereoisomer are formed in a 9:1 ratio. When (Z)-2-propenylsesamol is used as starting material, carpanone is accompanied by two carpanone diastereoisomers unknown so far in a 5:1:4 ratio. All three carpanone diastereoisomers have been separated by HPLC, and their structures have been elucidated unambiguously by NMR spectroscopy, DFT calculations, and spin work analysis. When the oxidation of 2-propenylsesamol with O2 is performed in the absence of any catalyst two diastereoisomeric benzopyrans are formed, probably as the result of a domino oxidation/intermolecular hetero Diels–Alder reaction. Under these conditions, carpanone is formed in trace amounts only.

The laccase-catalyzed ring opening of 2,5-dimethylfuran using air as an oxidant stereoselectively yields (Z)- or (E)-3-hexene-2,5-dione depending on the mediator employed: with TEMPO the (Z)-3-hexene-2,5-dione is formed, while a combination of TEMPO and violuric acid gives (E)-3-hexene-2,5-dione. The (Z)-selective ring cleavage was extended to a variety of symmetrical and unsymmetrical 2,5-dialkylfurans.

Depending on the ratio of the substrates and the reaction conditions, the Cu(I)-catalyzed domino reaction between bromobenzyl bromides and β-ketoesters exclusively yields either 4H-chromenes or naphthalenes.

The laccase-catalyzed domino reaction of o-phenylenediamine and benzaldehydes with aerial oxygen as the oxidant exclusively yields 2-aryl-1H-benzimidazoles in good to very good yields. It is easy to perform under very mild reaction conditions.

The enzymes tyrosinase and laccase from a crude extract of the button mushroom (Agaricus bisporus) can be employed to catalyze the domino reaction between phenol and various cyclic 1,3-dicarbonyls using atmospheric oxygen as the oxidizing agent and yielding annulated benzofuranes in a highly efficient and sustainable manner.

The efficient Cu(I)-catalyzed oxidative homocoupling of terminal alkynes in the presence of a base using an amine as a ligand and oxygen as an oxidant yields the symmetrical 1,3-diynes with yields of up to 99%. The outcome of the couplings critically depends on the proper choice of base and ligand as well as reaction conditions. Best results were observed with 2.0 mol % CuCl, 1.5 mol % TMEDA or DBEDA, and DBU or DABCO in acetonitrile.

Substituted 7-methyl-2H,5H-pyrano[4,3-b]pyran-5-ones and related heterocycles 3 were synthesized through an efficient domino Knoevenagel condensation/6π-electron electrocyclization. In vitro antiproliferative/cytotoxic activity evaluation was performed with human SH-SY5Y neuroblastoma cells and revealed IC50 values ranging from 6.7 to >200 μM. The compound that was most cytotoxic to the neuroblastoma cells, that is, 2-isobutyl-3-isopropyl-7-methyl-2H,5H-pyrano[4,3-b]pyran-5-one (3a), also exhibited necrotic effects on the human IPC melanoma cells.The title compounds were synthesized efficiently. Their in vitro antiproliferative/cytotoxic activity was evaluated with human SH-SY5Y neuroblastoma cells. IC50 values are ranging from 6.7 to >200 μM.

5-Hydroxy-3-oxopent-4-enoic acid esters can be efficiently transformed into the stable bis-potassium salts of the corresponding 5-hydroxy-3-oxopent-4-enoic acids, from which the sensitive acids are released in situ, the latter being converted into substituted 4-hydroxy-2H-pyran-2-ones, pyrazoles and isoxazoles under mild conditions; the efficiency of this method is demonstrated by the first synthesis of two naturally occurring pyrones.

The vitamin E family consists of 4 tocopherol and 4 tocotrienol compounds. During recent years, tocotrienols have gained increased interest due to their biological activities that are beyond the vitamin E activity. Here we report the engineering of plasmid-free Escherichia coli strains for an efficient synthesis of 2-methyl-6-geranylgeranyl-benzoquinol (MGGBQ), the central precursor for all four natural tocotrienol compounds.Heterologous genes needed for the in vivo synthesis of MGGBQ in E. coli (crtE, hpd, and hpt) were individually integrated into the chromosome of E. coli. The yield of MGGBQ after cultivation of the plasmid-free recombinant E. coli strain was significantly higher (604 μg/g cdw) compared to an E. coli strain that carries these biosynthesis genes on a multi-copy expression plasmid (325 μg/g cdw). Further chromosomal integration of an additional copy of the isopentenyl-diphosphate isomerase gene (idi) and a subsequent increase in expression level of the deoxy-xylulose synthase gene (dxs) increased the MGGBQ yield by 80% (1110 μg/g cdw) and 135% (1425 μg/g cdw), respectively. MGGBQ which accumulated in the membrane fraction of the recombinant E. coli cells was isolated and its structure was completely elucidated by 1D and 2D NMR and MS measurements. The engineered, plasmid-free E. coli strain is a promising host for the heterologous in vivo production of tocotrienol and its derivatives.Highlights► Construction of a plasmid-free E. coli strain for the synthesis of MGGBQ. ► Chromosomal integration led to higher production of MGGBQ than multi-copy plasmid. ► Formation of MGGBQ increased by enhanced expression of isoprenoid synthesis genes. ► Isolation and structural elucidation of the heterologously produced MGGBQ. ► The system has potential applications for the efficient formation of tocotrienols.

Cu(I)-catalyzed reaction of o-bromobenzaldehydes with β-ketoesters using Cs2CO3 as a base and 2-picolinic acid as an additive proceeds under mild conditions and gives access to substituted naphthalenes in a single step with yields ranging from 71 to 86%. The new annulation process relies on a domino Knoevenagel condensation/C-arylation/1,2-addition/carboxylic acid cleavage. The annulation can also be achieved with o-iodobenzaldehyde.

The Lewis acid-catalyzed domino 1,2-addition/1,4-addition/elimination between (Z)-3-hexene-2,5-dione and 1,3-dicarbonyls delivers 3-methyl-6,7-dihydrobenzofuran-4(5H)-ones exclusively with yields up to 82%. The combination of this new process with the laccase-catalyzed formation of (Z)-3-hexene-2,5-dione by oxidative cleavage of 2,5-dimethylfuran allows for the synthesis of 6,7-dihydrobenzofuran-4(5H)-ones starting directly from 2,5-dimethylfuran.