Synthesis of chalcones bearing 2-hydroperoxy-3-methyl-3-butenyl or 2-hydroxy-3-methyl-3-butenyl group from prenylated chalcones

Abstract

Chalcones bearing 2-hydroperoxy-3-methyl-3-butenyl or 2-hydroxy-3-methyl-3-butenyl groups, such as xanthoangelol E (1a), xanthoangelol D (2a), psorachalcone A (2?b), xanthohumol D (2c), and related derivatives were first synthesized by using the ene reaction of prenylated chalcones with singlet oxygen.     

Iodocyclization of S-allyl derivatives of 3-mercapto-4-methyl-1,2,4-triazole

It has been established that iodocyclization of 3-(2-methyl-2-propenyl)thio-4-methyl-1,2,4-triazole occurs regioselectively with annelation of the thiazole ring, 3-(3-methyl-2-butenyl)thio-4-methyl-1,2,4-thiazole with annelation of the thiazine ring, and 3-allylthio-4-methyl-1,2,4-triazole with annelation of both rings to form derivatives of [1,3]thiazolo[3,2-b][1,2,4]triazolium and [1,2,4]triazole[5,1-b][1,3]thiazinium iodides.     

The molecular structure of 4a, 5, 8, 8a-tetrahydro-11, 14-dimethoxy-7-methyl-4a-(3-methyl-2-butenyl)-5, 8a-o-benzeno-1, 4-naphthoquinone

A novel natural product, microphyllone, has been isolated from Ehretia microphylla² together with baurenol and ursolic acid. Spectroscopic techniques, derivative formation and finally X-ray diffraction have been utilized in the structure elucidation of microphyllone. The structure appears to be 4a, 5, 8,8a - tetrahydro -11,14- dihydroxy-7-methyl-4a-(3-methyl-2-butenyl)-5, 8a-o-benzeno-1, 4-naphthoquinone.     

Ab initio studies of the allylic hydroxylation: DFT calculation on the reaction of 2-methyl-2-butene with selenium dioxide

The mechanism of the allylic oxidation of 2-methyl-2-butene with selenium dioxide has been investigated by ab initio quantum mechanics. Transition states for two major steps (an ene reaction and a [2,3]-sigmatropic rearrangement) of this reaction have been optimized by the B3LYP/6-311+G(d,p) method. A comparison of the energies of the transition states shows that the anti-endo and syn-endo approaches are the efficient routes in the ene reaction and the methyl (C4) group is sited in a pseudo-equatorial environment in cyclic transition states during the [2,3]-rearrangement. Calculations also show the kind of the terminal alkyl (C4) substituents may control (E)-selectivity in the formation of the allylic alcohols.     

1H n.m.r. spectra of some bicyclic compounds: I—relative configurations of the diastereomeric endo-α-methyl-5-norbornene-2-methanols,the corresponding saturated analogues,and their cyclization ether products

The configurational and conformational relationship at C-2 and C-α in the two racemic diastereomeric endo-α-methyl-5-norbornene-2-methanols and the corresponding saturated endo-α-methyl-2-norbornanemethanols were determined by first-order analysis of the ¹H n.m.r. spectra of these compounds and of their cyclization ether products, i.e. 3-methyl-2-oxatricyclo[4.2.1.0^4,8]nonanes and 5-methyl-4-oxatricyclo[4.3.0.0^3,8]nonanes. In addition, the conformational preference of the hydroxyl group in the unsaturated and saturated alcohols was confirmed by the lanthanide induced shift technique, using Eu(fod)₃ as shift reagent, combined with a computer program involving various conformations of the –CHOHMe group.     

Thermal decomposition products of methyl 1,5-diphenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2-ene-6-exo-carboxylates

Methyl 1,5-diphenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2-ene-6-exo-carboxylates at 138°C undergo decomposition via elimination of nitrogen molecule with formation in each case of five products. Two products are methyl 1,3-diphenyl(or 1-methyl-3-phenyl)bicyclo[1.1.0]butane-2-endo- and -exo-carboxylates, and the three others are derivatives of buta-1,3-diene, methyl (Z)-2-benzylidene-3-phenyl(or 3-methyl)but-3-enoate and methyl (E)- and (Z)-3,4-diphenyl(or 4-methyl-3-phenyl)penta-2,4-dienoates. The formation of these products may be rationalized assuming intermediacy of substituted allylcarbene which undergoes both intramolecular cycloaddition and rearrangements involving 1,2-hydride and 1,2-vinyl shifts.     

Investigation of the Montmorillonite clay-catalyzed [1,3] shift reaction of 3-methyl-2-butenyl phenyl ether

The [1,3] shift reaction of 3-methyl-2-butenyl phenyl ether was catalyzed more effectively by Montmorillonite K10 clay than Montmorillonite KSF clay, and proceeded with greatest ortho-selectivity in carbon tetrachloride at room temperature.     

Thermally induced opening of the diaziridine ring in 6-aryl-2-methyl-1,5-diazabicyclo[3.1.0]hexanes

Thermally induced opening of the diaziridine ring in 6-aryl-2-methyl-1,5-diazabicyclo[3.1.0]-hexanes at the carbon-nitrogen bond is characterized by low regioselectivity; isomerization of unstable intermediate azomethine imines leads to mixtures of the corresponding 1-arylmethyl-5-methyl-4,5-dihydro-1H-pyrazoles and 1-arylmethyl-3-methyl-4,5-dihydro-1H-pyrazoles at a ratio of ～6:5. Analogous regioselectivity in opening of the three-membered ring is observed in the presence of phenyl isocyanate. In this case, adducts with cis arrangement of the aryl and methyl groups are formed as the major products (cis/trans ratio ～3:1).     

Darstellung,Eigenschaften und Kristallstruktur von [2-(1′-methyl-4-imidazolyl)phenyl-1-C,3′-N]acetylacetonatopalladium(II)

Synthesis, Properties, and Structure of [2-(1′-methyl-4-imidazolyl)phenyl-1-C,3′-N]-palladium(II) Acetylacetonate The reaction of Di-μ-chloro-bis[2-(1′-methyl-4-imidazolyl)phenyl-1-C,3′-N]palladium(II) with Thallium(I) acetylacetonate yields [2-(1′-methyl-4-imidazolyl)phenyl-1-C,3′-N]palladium(II) acetylacetonate. The complex crystallizes monoclinic in the space group P2₁/n with the lattice constants a = 1302.4(3), b = 836.0(2), c = 1341.3(3) pm, β = 93.69(3)°. Pd has a squareplanar coordination by two O atoms of acetylacetonate, the N atom of the imidazole ring, and the C atom of the phenyl group. I.r., n.m.r., and mass spectra are reported.     

Enantioselective synthesis of (R)- and (S)-2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxamides

Enantiomers of 2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxamides bearing different substituents in the aromatic ring are obtained by the cyclization of (R)-monomethyl 2-methyl-2-(2-nitrophenoxy)malonates with the participation of the carboxy and methoxycarbonyl group, respectively.     

Exo- and endo-palladacycles derived from (4R)-phenyl-2-oxazolines

Two novel oxazoline-derived palladacycles bearing an endo- or exo-CN bond were prepared by direct ortho-palladation of (R)-2,4-diphenyl- or (R)-2-methyl-4-phenyl-2-oxazolines, respectively. The structures of the palladacycles' dimeric forms and corresponding mononuclear PPh₃-derivatives were confirmed by IR, ¹H, ¹³C and 2D NMR spectroscopy. An X-ray diffraction study of the μ-chloro-dimeric cyclopalladated derivative of (R)-2,4-diphenyl-2-oxazoline proved the endo structure of the palladacycle.     

2-甲基-6-(3-甲基-2-丁烯基)对苯二醌的合成

以邻甲基苯酚为原料,与1-氯-2-甲基-2-丁烯反应生成2-甲基-6-(3-甲基-2-丁烯基)苯酚,然后催化氧化得到目标产物2-甲基-6-(3-甲基-2-丁烯基)对苯二醌。该合成路线简单,易于操作,最终收率51%。     

Anti-isohumulone and its derivatives

Three new humulone derivatives have been isolated and identified as: 3,4-dihydroxy-2-(3-methyl-2-butenyl)-4-(4-methyl-3-pentenoyl)-2-cyclopentenone (6);4-ethanoyl-3,4-dihydroxy-2-(3-methyl-2-butenyl)-2-cyclopentenone (7) and 3,4-dihydroxy-2-(3-methyl-2-butenyl)-2-cyclopentenone (8), respectively. They arise by deacylation of anti-isohumulone (3_a), which is formed from humulone (1a) following an isomerization with ring contraction in opposite direction than the usual one producing isohumulones (2a).     

5-Nitroisocoumarins from tandem Castro-Stephens coupling—6-endo-dig cyclisation of 2-iodo-3-nitrobenzoic acid and arylethynes and ring-closure of methyl 2-alkynyl-3-nitrobenzoates with electrophiles

Reaction of 2-iodo-3-nitrobenzoic acid with arylalkynyl copper(I) reagent gave 3-aryl-5-nitroisocoumarins. Castro-Stephens coupling was followed by in situ Cu-catalysed ring-closure. ¹H NMR and X-ray crystallography showed the cyclisations to be 6-endo, contrasting with reports of 5-exo cyclisation of analogous 2-iodobenzoate esters with alkynes. Sonogashira couplings of methyl 2-iodo-3-nitrobenzoate with phenylacetylene and with trimethylsilylacetylene gave the corresponding 2-alkynyl-3-nitrobenzoate esters. With HgSO₄, the phenylalkyne underwent 6-endo cyclisation to give 5-nitro-3-phenylisocoumarin. The disubstituted alkyne esters gave 4-phenylselenylisocoumarins with PhSeCl. 5-Nitro-3-phenyl-4-phenylselenylisocoumarin shows significant sterically-driven distortion of the isocoumarin ring. Reaction of methyl 3-nitro-2-phenylethynylbenzoate with ICl gave the 4-iodoisocoumarin. Thus the nitro group tends to direct these electrophile-driven cyclisations towards the 6-endo mode.     

Stereoselective lithiation and alkylation and aldol reactions of chiral 5-methyl-3-(o-aryl)-oxazolidinones

Alkylation and aldol reactions carried out on axially chiral, diastereoenriched oxazolidinedione derivatives were found to be highly stereoselective with respect to substitution at the 5-position of the oxazolidindione ring. Thus, diastereoenriched 5-methyl-3-(o-iodophenyl)-2-thioxo-4-oxazolidinone and 5-methyl-3-(o-aryl)-2,4-oxazolidinediones were prepared and lithiated at C-5 of the oxazolidine ring and the subsequent electrophilic quench with alkyl halides or benzaldehyde yielded products with the same diastereomer ratios as the starting materials.     

Access to racemic and enantioenriched 3-methyl-4-chromanones: catalysed asymmetric protonation of corresponding enolic species as the key step

Brønsted acids induced the intramolecular cyclisation of 3-aryloxypropanoic esters affording 3-methyl-4-chromanones, which have been transformed into the corresponding racemic benzyl β-oxoesters. These latter esters, in the presence of hydrogen and catalytic amounts of both palladium and (endo, endo) aminoborneol, led to optically active chromanones with up to 75% ee through a deprotection-decarboxylation-protonation cascade reaction.     

Regioselective radical cyclization initiated by the reaction of allylic hydroperoxides with iron(II) sulfate

Treatment of 1-methyl-2-methylene-1-cyclohexyl hydroperoxide with a mixture of FeSO₄/CuCl₂ yielded 1-(1-chlorocyclohexyl)ethanone as the major product consistent with 6-endo-trig cyclization of the intermediate 5-acetylhex-5-enyl radical. This strategy was extended to the ring enlargement of a series of 1-isopropenylcycloalkyl hydroperoxides. Regioselective 7- or 8-endo-trig cyclization reactions could be achieved by treatment of the corresponding cyclopentyl or cyclohexyl hydroperoxides with either a mixture of FeSO₄/CuCl₂ or with FeSO₄ only. The influence of substituents on the efficiency of the 8-endo-trig cyclization process was also explored.     

Amidrazones 11. Rearrangement of 1-allyl-substituted-4,5-dihydro-1-methyl-1H-pyrazolium bromides

1-Methyl-2-(2-propenyl)-3-pyrazolidinimine ( 5 ) was obtained by treatment of 3-amino-4,5-dihydro-1-methyl- 1-(2-propenyl)-1H-pyrazolium bromide ( 4 ) with ethanolic sodium ethoxide. Similar treatment of the analogous 2-(2-butenyl) and 2-(3-phenyl-2-propenyl)-substituted salts 12 and 15 gave 1-methyl-2-(1-methyl-2-propenyl)-3- pyrazolidinimine ( 13 ) and 1-methyl-2-(1-phenyl-1-propenyl)-3-pyrazolidinimine ( 16 ) respectively.     

Nitropyrazoles 17. Synthesis of 1-(3,5-dinitrophenyl)-4-methyl-3,5-dinitropyrazole and the study of its chemical transformations

A new one-step method for the synthesis of 4-methyl-3(5)-nitropyrazole by nitration of 4-methylpyrazole is developed. Arylation of 4-methyl-3(5)-nitropyrazole with 1,3,5-trinitrobenzene gives 1-(3,5-dinitrophenyl)-4-methyl-3-nitropyrazole, nitration of which leads to 1-(3,5-dinitrophenyl)-4-methyl-3,5-dinitropyrazole. The action of 1 equiv. of an O- or S-nucleophile (phenolate, p-chlorobenzenethiolate and ethoxide ions; anions of glycolanilide and thioglycolanilide) on 1-(3,5-dinitrophenyl)-4-methyl-3,5-dinitropyrazole led to the substitution of the 5-NO₂ group of the pyrazole ring; under the action of one more equivalent of a nucleophile the NO₂ group of the benzene ring was substituted. The substitution product of the anion of thioglycolanilide for the 5-NO₂ group undergoes the intramolecular cyclization — oxidative nucleophilic hydrogen substitution in the benzene ring under the action of K₂CO₃.     

Tautomerism of Aza heterocycles: V. Structure of the spontaneous transformation products of 5-methyl-2-phenyl-3,3a,4,5,6,7-hexahydro-2H-pyrazolo-[4,3-c]pyridin-3-one in crystal and solution

5-Methyl-2-phenyl-3,3a,4,5,6,7-hexahydro-2H-pyrazolo[4,3-c]pyridin-3-one exists as zwitterion with a proton localized on the nitrogen atom of the piperidine ring and negative charge delocalized over the pyrazololate fragment. The compound is stable in crystal but ustable in solution. Its chromatographic purification and attempts to recrystallize or synthesize by condensation of phenylhydrazine with alkyl 1-methyl-4-oxopiperidin-3-carboxylate on heating in alcohols or benzene lead to the formation of a complex mixture of products. Among these products, we isolated and identified 3a,3a′-methylenebis(5-methyl-2-phenyl-3,3a,4,5,6,7-hexahydro-2H-pyrazolo[4,3-c]pyridin-3-one), 1-methyl-3-(2-phenylhydrazinylidene)pyrrolidin-2-one, and 5-methyl-2-phenyl-3,5,6,7-tetrahydro-2H-pyrazolo[4,3-c]pyridine. The structure of methyl 3-(2-phenylhydrazinylidene)-4,5-dihydro-3H-pyrrole-2-carboxylate and 3a,5-dimethyl-2-phenyl-3,3a,4,5,6,7-hexahydro-2H-pyrazolo[4,3-c]pyridin-3-one was proved by NMR spectroscopy. 3a,5-Dimethyl-2-phenyl-3,3a,4,5,6,7-hexahydro-2H-pyrazolo[4,3-c]pyridin-3-one was isolated as hydrochloride hydrate whose structure was determined by X-ray analysis.