Synthesis and photochromic reactivity of macromolecules incorporating four dithienylethene units

Two macrocycles bearing four dithienylethene units were synthesized. Upon irradiation of the macrocycles 5 and 6 with ultraviolet light, only one or two photo-induced cyclization reaction occurs. Each isomers were isolated and analyzed by ¹H NMR spectrum. The quantum yield of 5 and 6 are 0.58 and 0.64, respectively. The high value is due to the presence of enforced antiparallel conformation in the macrocycles 5 and 6.     

A ring-fission/C–C bond cleavage reaction with an N-alkyl-N-methyl-N-[(5-phenyl-1,2,4-oxadiazol-3-yl)methyl]amine

The reaction of N-(3,4-dichlorophenethyl)-N-methylamine (1) with 3-chloromethyl-5-phenyl-1,2,4-oxadiazole (2) was investigated. Employment of an equimolar amount of 1 and 2 in the presence of potassium carbonate led to the expected tertiary amine 3 (N-[(3,4-dichlorophenyl)ethyl]-N-methyl-N-[(5-phenyl-1,2,4-oxadiazol-3-yl)methyl]amine), whereas an excess of 1 and prolonged reaction time resulted in ring fission of the oxadiazole system in 3 and finally in the formation of N′-benzoyl-N-[(3,4-dichlorophenyl)ethyl]-N-methylguanidine (4) and N,N′-bis[(3,4-dichlorophenyl)ethyl]-N,N′-dimethylmethanediamine (5). The structures of products 3–5 were determined by means of ¹H and ¹³C NMR-spectroscopy, mass spectrometry and IR-spectroscopy, for 3 (as picrate) and 4 also X-ray structure analysis was employed. A possible mechanism of the reaction pathway leading to compounds 4 and 5 is proposed.     

Unprecedented cyclisations of calix[4]arenes under the Mitsunobu protocol. Part 3: Thiacalix[4]crowns versus dimers

Intermolecular couplings versus intramolecular ring closures were observed in the reaction of p-tert-butylthiacalix[4]arene and diethylene glycols affording dimers 2 and/or the inherently chiral 1,2-thiacalix[4]crown-3 derivatives 5 under the Mitsunobu protocol. The enantiomeric separation of 5a was achieved by chiral HPLC. The reaction of thiacalix[4]monocrowns 1 with diethylene glycols failed to give crowned thiacalix-tubes 7, instead biscrowns 8 were formed. Partially alkylated double thiacalix[4]arenes 10, 11 were obtained via the base promoted alkylations of a thiacalixarene dimer 2a containing diethyleneoxy linkers.     

Optically active nitroalkenes—synthesis, addition reactions and transformation into amino acids

Optically active nitroalkenes 4 were synthesized via Henry reaction. Conjugate addition of vinylmagnesium bromide to 4 gave nitroalkane syn-5 while cyclopropanation with sulfur ylides or dibromocarbene afforded nitrocyclopropanes 8, 10 and 11 in a diastereoselective manner. These products were used to synthesize optically active β-amino acids 7 and 16 as well as cyclopropane γ-amino acids 19 and 20 by reduction of the nitro group and oxidative cleavage of the dioxolane substituent.     

Palladium-catalyzed hydrocarbonation of methyleneaziridines with carbon pronucleophiles

The reaction of methyleneaziridine 1 with carbon pronucleophiles (2, H-CR₃) proceeds smoothly in the presence of a palladium catalyst affording the corresponding hydrocarbonation products 5 in good to high yield.     

Synthesis of the hydroazulene portion of guanacastepene A using a [2.3]sigmatropic sulfoxide rearrangement: observations on silyl enol ether electrophilic chemistry for the introduction of the C-13 hydroxyl group

The intermediate 6 can be converted into enone 13 using a [2.3]sigmatropic sulfoxide rearrangement as the key transformation. The C-13 hydroxylation of 13 was studied, and found to give 14 (epimeric to guanacastepene A). Examination of silyl enol ethers of 13 demonstrated the ready isomerization of the kinetic silyl enol ether into the more stable thermodynamic silyl enol ether under mild electrophilic reaction conditions.     

New dense fluoroalkyl-substituted imidazolium ionic liquids

New mono and polyfluoroalkyl-substituted ionic liquids have been synthesized and characterized. The neat reaction of 1-methylimidazole (1a) with 1,1,1-trifluoro-3-iodopropane (2a) at 80°C formed the quaternary salt, 1-methyl-3-trifluoropropylimidazolium iodide (3), in 90% yield. Similarly, sodium imidazole (1b) gave good yields of the quaternary salts, 1,3-bis(trifluoropropyl)imidazolium iodide (3b) with an excess of 2a, and 1,3-bis(monofluoropropyl)imidazolium bromide (3c) with an excess of 1-fluoro-3-bromopropane (2b). In water as solvent, metathesis reactions of 3 with KPF₆, LiN(SO₂CF₃)₂ and KSO₃CF_3, and of 3b and 3c with KPF₆ and LiN(SO₂CF₃)₂ led to 4a–c, 4d,e, and 4f,g, respectively, in good isolated yields. Some of the di(polyfluoroalkyl)imidazolium salts are liquids with densities in excess of 1.8 g/cm³.     

Synthesis of arylglycines via the Dötz benzannulation reaction

Arylglycines are biologically active -amino acids. Our approach toward the synthesis of arylglycines features the Dötz benzannulation reaction between a variety of Fischer chromium carbene complexes 3 and alkyne 4. This leads to the formation of protected arylglycinols 5, which can be transformed to the corresponding N-protected arylglycines.     

Novel transformation of 2-substituted alkyl 1-indanone-2-acetates to 6-substituted 3,4-benzotropolones through sequential reduction and oxidation processes using Sm(II) and Ce(IV) salts

When 2-substituted alkyl 1-indanone-2-acetates 1 were treated with samarium diiodide, 3-substituted 2-hydroxy-2,3-methano-1-oxo-1,2,3,4-tetrahydronaphthalenes 4 were obtained. The reaction is proposed to proceed through a rearrangement initiated by intramolecular ketone–ester coupling. Oxidation of these products 4 or their silyl ethers 13 by ceric(IV) ammonium nitrate involving regioselective bond cleavage of their bicyclo[4.1.0]-rings produced the corresponding benzotropolone derivatives 10.     

Site-recognition of one of the two alkoxy carbonyl groups present in the dienophile for Diels–Alder reaction

Recognition of one alkoxy carbonyl group from the two in a molecule by a Lewis acid was investigated using 1a–e in the Diels–Alder reaction with diene 6. Combination of 1a and BF₃·OEt₂ provided the highest efficiency to afford 7a, thus showing evidence for the site-selective coordination of BF₃·OEt₂ to the MOM-oxy carbonyl group in 1a. Furthermore, the generality and high reactivity of this combination were confirmed with dienes 11–14.     

Synthesis and properties of 2-azidodeoxyadenosine and its incorporation into oligodeoxynucleotides

2-Azidodeoxyadenosine (7) was conveniently synthesized from deoxyguanosine (2) by use of a combined reagent of TMSN₃–BuONO. The structure of the tautomer of the azido derivative was determined by ¹H NMR. Reaction of 7 with iPr₂NP(OEt)₂ gave an intermediate 10 of the Staudinger reaction. Incorporation of 7 into a DNA 13mer resulted in a significant decrease of the T_m value of the DNA duplex upon hybridization with the complementary strand. The thermal stability was discussed based on the hydrogen bond energy and electrostatic repulsion.     

Asymmetric synthesis of (2-carbamoyloxy-1-alkenyl)cyclopropanes by intramolecular cycloalkylation

Enantioenriched, diastereomerically pure (2-carbamoyloxy-1-alkenyl)cyclopropanes 22 are easily prepared via deprotonation of different allyl carbamates with n-butyllithium and (−)-sparteine (4). The mechanism of the cyclization reaction was determined and several substituted (S)-configured vinylcyclopropanes 32 were synthesized by two different methods. The configurational stability of the intermediate lithiated allyl carbamates and the half-time of epimerization were investigated in a series of silylation experiments, achieving up to 90% ee in the kinetically controlled enantiotopos-differentiating deprotonation.     

Thermal rearrangements of bis-allenyl thiosulfonates. Synthesis of novel thienothiophene and thieno-oxathiine derivatives

The synthesis and thermal rearrangement of bis-allenyl thiosulfonates are described. Bis-γ,γ-disubstituted allenyl thiosulfonates have been prepared by disproportionation of the corresponding allenesulfinic acids. On heating, these compounds unexpectedly rearrange to a mixture of 1H,3H-thieno[3,4-d][1,2]oxathiine-3-oxide 8, 1H,3H-thieno[3,4-c]thiophene-2,2-dioxide 9, and 3-alkyl-4-alkenylthiophene 10. A tentative reaction mechanism involving sequential sigmatropic rearrangements and cyclizations is suggested.     

A concise total synthesis of (−)-dehydroclausenamide utilizing the novel formation of cis-epoxide as the key step

The asymmetric total synthesis of (−)-dehydroclausenamide 1 was accomplished through a concise and efficient synthetic route employing as the key step the novel formation of cis-epoxy amide 7, which was resulted from the reaction of starting material 4 bearing an optically pure erythro vicinal diol unit with 5H-3-oxa-octafluoro pentanesulfonyl fluoride (HCF₂CF₂OCF₂CF₂SO₂F) in the presence of 1,8-diazabicyclo[5.4.0]-7-undecene (DBU).     

Studies on the syntheses of heterocycles from 3-arylsydnone-4-carbohydroximic acid chlorides with N-arylmaleimides, [1,4]naphthoquinone and aromatic amines

3-Arylsydnone-4-carbohydroximic acid chlorides (1) could react with N-arylmaleimides (3a–b) or 2-methyl-N-phenylmale-imide (3c) to give 3-(3-arylsydnon-4-yl)-5-aryl-3a,6a-dihydro-pyrrolo[3,4-d]isoxazole-4,6-diones (4a–h) or 6a-methyl-3-(3-arylsydnon-4-yl)-5-phenyl-3a,6a-dihydro-pyrrolo[3,4-d]isoxazole-4,6-diones (4i–l), respectively. However, 3-(arylsydnon-4-yl)-naphtho[2,3-d]isoxazole-4,9-diones (6a–d) were obtained in good yield by the reaction of carbohydroximic acid chlorides 1 with [1,4]naphthoquinone. Furthermore, 2-(3-arylsydnon-4-yl)benzoxazoles (9a–d) and 2-(3-arylsydnon-4-yl)benzothiazoles (9e–h) were obtained via the reaction of carbohydroximic acid chlorides 1 with ortho-substituted aromatic amines 7a and b.     

Synthesis of a simplified sarcodictyin analogue which retains microtubule stabilising properties

A strategy featuring ring-closing metathesis as key reaction is applied to the synthesis of the sarcodictyin analogue 15. The precursor diene is accessed via a brief and efficient protocol, employing multiple stereoselective allylations. Simplified analogue 15 retains microtubule stabilising properties.     

Highly efficient and mild synthesis of variously 5-substituted-4-carbaldehyde-1,2,3-triazole derivatives

Synthesis of variously 5-substituted-4-carbaldehyde-1,2,3-triazole derivatives 2 was accomplished by reacting sodium azide with ,β-acetylenic aldehydes 1 in DMSO at room temperature. Therefore, the reaction remains basic avoiding the generation of the hazardous explosive HN₃, resulting in a safe process. This mild and general reaction was instantaneous and was essentially quantitative.     

Asymmetric Diels–Alder reactions in supercritical carbon dioxide catalyzed by rare earth complexes

The rare earth(III) salt catalysed asymmetric Diels–Alder reaction of cyclopentadiene with a chiral dienophile in supercritical carbon dioxide (scCO₂) proceeded rapidly to give the adduct with a higher diastereoselectivity than that in dichloromethane; Yb(ClO₄)₃ gave the endo adduct with value up to 77% de at 40°C, 8 MPa. The chiral rare earth diketonate catalyzed hetero Diels–Alder reaction of the Danishefsky's diene with benzaldehyde gave a higher yield and an enantioselectivity in scCO₂ than that in dichloromethane. Scandium/pybox 8a complex catalysed asymmetric Diels–Alder reaction of 3-crotonoyl-2-oxazolidinone with cyclopentadiene in the presence of MS4A proceeded smoothly in scCO₂ to give the endo adduct 10 in a good yield with up to 88% ee.     

Synthesis and characterization of low generation halogenated linear poly(arylpropargyl)ether (PAPE) branches via selective palladium catalyzed coupling reactions

A rapid convergent synthesis of first- and second-generation halogenated linear poly(arylpropargyl ether) branches 7 and 10 is described. The key step of the sequence studied involves a selective Sonogashira–Linstrumelle (S–L) cross-coupling reaction of aryl iodides with alkynes bearing an sp²-carbon–iodine bond. Application to the synthesis of functionalized first-generation poly(arylpropargylether) stars having a benzene-1,3,5-tricarboxylic acid core has been realized.     

Lower rim substituted tert-butylcalix[4]arenes. Part 8: Calix[4]arenes with dialkoxyphosphoryl functions. Synthesis and complexing properties

New compounds: 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diisopropoxyphosphorylpropoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-methoxyethoxyphosphorylpropoxy)calix[4]arene (2) were synthesized and their ionophoric properties in ion-selective membrane electrodes were studied in comparison with already described by us 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diethoxyphophorylpropoxy)calix[4]arene (3). Complexes of 1 with calcium(II), lanthanum(III), europium(III) and gadolinium(III) nitrates were prepared in direct reaction of the ligand and appropriate metal salts. They were characterized by spectral data (IR, UV/Vis, luminescence, NMR, ESI-MS) and elemental analysis. The similarity in complexing behavior of the (dialkoxyphosphoryl)propoxy-calix[4]arenes toward calcium and some lanthanides was observed.