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.     

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.     

Novel sesquiterpenes and a lactone from the Jamaican sponge Myrmekioderma styx

Two novel sesquiterpenes, styxone A (1) and styxone B (2), and a novel lactone, styxlactone (3), were isolated from the Jamaican sponge Myrmekioderma styx. Their structures were elucidated by detailed ¹H, ¹³C and 2D NMR data and the absolute stereochemistry of styxone A and B was determined by CD spectra. Styxone A represents a novel sesquiterpene skeleton. (S)-(+)-Curcuphenol (4), (S)-(+)-curcudiol (5), and abolene (6) were also isolated. An activity enhancement by cyanthiwigin B (7) to curcuphenol was observed in the antimicrobial assays when the two compounds were administered together.     

5-Aminocyclopentadienes by intramolecular addition of enolether to aminoallene functionalities

3-(1-Alkoxyvinyl)-1-aminoallenes 6 were generated by conjugate addition of acyclic and cyclic (1-alkoxyvinyl)cuprates with the semicyclic propyne iminium salt 4. They isomerized smoothly into spiroannellated cyclopentadienes 7 through a 1,5-cyclization that in some cases occurred already at ≤20°C. (1-Methoxyallenyl)cuprates reacted with salt 4 in a 2:1 ratio to give the 5,5-dimethoxy-4-methylenepentalene-1-spiro-2′-dihydroindole derivative 10. The thermal isomerization of morpholinoallene 12 into cyclopentadiene 13 indicates that the novel 1,5-cyclization can be extended to other 3-(1-alkoxyvinyl)-1-aminoallenes as well.     

Synthesis of N-Fmoc 3-(4-(di-(tert-butyl)phosphonomethyl)phenyl)pipecolic acid as a conformationally constrained phosphotyrosyl mimetic suitably protected for peptide synthesis

Phosphonomethylphenylalanine (Pmp, 2) has shown wide utility as a hydrolytically stable phosphtyrosyl (pTyr, 1) mimetic, particularly in Src homology 2 (SH2) domain-binding peptides. (2S,3R)-3-(4-(phosphonomethyl)phenyl)pipecolic acid (3) represents a variant of Pmp having φ and χ₁ torsion angles constrained through incorporation into the piperidinyl ring structure contained within pipecolic acid. Reported herein is the enantioselective preparation of 3, in an orthogonally protected form (4) suitable for use in peptide synthesis. Stereochemistries at both the 2- and 3-positions are derived inductively from a single chiral center provided by the commercially available Evans chiral auxiliary, (4S)-4-benzyl-1,3-oxazolidin-2-one. Incorporation of 4 into a Grb2 SH2 domain-directed tripeptide (18) showed that Grb2 SH2 domain-binding affinity was reduced relative to the parent Pmp-containing tripeptide (19). Although conformational constraint did not enhance affinity in this case, novel amino acid analogue 4 may serve as a useful tool for the induction of defined phosphotyrosyl geometry in peptides directed at other signal transduction targets.     

Formation of 1,2,4-trioxolanes via 9,10-dicyanoanthracene(DCA)-sensitized photo-oxygenation of 2,2-diaryl-3-(2,2-diarylvinyl)oxiranes

9,10-Dicyanoanthracene-sensitized photo-oxygenation of 2,2-diaryl-3-(2,2-diarylvinyl)oxiranes 3 in acetonitrile did not afford the corresponding 1,2,4-trioxepines 4, but 1,2,4-trioxolanes 7. The structural assignment of 7 was reported, and the mechanism of the formation of 7 was proposed.     

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.     

Edulisones A and B, two epimeric benzo[b]oxepine derivatives from the bark of Aglaia edulis

Two benzo[b]oxepine derivatives, edulisones A (1) and B (2), were isolated from the bark of Aglaia edulis, collected in Indonesia. The relative stereochemistry of 1 was determined by single-crystal X-ray diffraction analysis. Treatment of compounds 1 and 2 with lithium hydroxide produced the same hydrolysis products, 1a and 1b, as a result of cleavage of the pyrrolidine ring to an alkylated amide mixture in each case, which demonstrated that these substances are epimeric at their 2-aminopyrrolidine moiety.     

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.     

Application of organolithium and related reagents in synthesis. Part 25: Novel specific synthesis of the 4-arylisochroman-3-acetic acids via conversion of benzoic acids

The transformation of the benzanilides 1 into 4-arylisochroman-3-acetic acids 8 applying the following sequence of reactions is described. At first, the 3-arylphthalides 3 were obtained via metallation [n-BuLi] of benzanilides 1 and subsequent treatment of the generated bis-lithiated anilides 2 with aromatic aldehydes. Next, the 3-arylphthalides 3 were reduced [LiBH₄] to phthalanes 5 and then, via reductive metallation [Li/C₁₀H₈] and reaction of the generated bis-lithiated species 6 with dimethylformamide, 3-hydroxy-4-arylisochromans 7 were produced. In the final step the isochromans 7 were treated with 1-methoxy-1-trimethylsilyloxyethene in the presence of titanium tetrachloride and furnished 4-arylisochromans-3-acetic acid methyl esters 8 as trans stereoisomers (Ψ-e/e).     

Engineering reactions in crystals: suppression of photodecarbonylation by intramolecular β-phenyl quenching

The photochemical reactivity of cis- and trans-2-(p-carboxybenzyl)-2,6-diphenyl-6-vinylcyclohexanone, cis-1 and trans-1, was investigated in solution and in the crystalline solid state. Photochemical decarbonylation in solution proceeded in excellent yields to give cis- and trans-1-(p-carboxybenzyl)-1,2-diphenyl-2-vinylcyclopentanes cis-2 and trans-2 along with 3-(p-carboxybenzyl)-1,3-diphenylcycloheptene 3. Reactions in crystals were suppressed by a stereospecific quenching interaction between the benzyl substituent and the carbonyl oxygen in the crystalline ketone.     

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.     

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.     

Odorless substitutes for foul-smelling thiols: syntheses and applications

Several alkanethiols and p-alkylphenylmethanethiols were synthesized, and their odors were compared with those of ethanethiol and benzyl mercaptan by human and instrumental sensors. Among the various thiols analyzed, 1-dodecanethiol (1) and p-heptylphenylmethanethiol (3) were revealed to be odorless. 1-Dodecanethiol (1) has been used instead of ethanethiol for dealkylation of ethers, and p-heptylphenylmethanethiol (3) can replace benzyl mercaptan in the preparation of a 1,3-mercapto alcohol from an ,β-unsaturated ketone. These odorless thiols will greatly improve the physical environment of the researcher working with these foul-smelling compounds.     

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).     

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.     

Synthesis of helianane, an unusual marine sesquiterpene employing ring-expansion by flash vacuum thermolysis

A total synthesis of the marine sesquiterpene helianane 1 is described involving the thermal rearrangement of the benzoxabicyclo[4.2.0]octenone 4 to generate the dienone 5 incorporating the benzoxocane ring system of 1. This dienone was converted to the key ketone 11, which on interaction with methylmagnesium iodide followed by hydrogenation of the resulting alkene 18 furnished helianane 1.     

Synthesis of chiral lithium carbamates from (S)-2-(N,N-dialkyl-aminomethyl)pyrrolidines and (S)-methoxymethylpyrrolidine

A convenient synthesis of chiral lithium N-alkyl carbamates 1a–4a from chiral pyrrolidines 1–4, LiH and CO₂ is described. The yields are good to excellent. A combined experimental (¹H, ⁶Li-HOESY, cryoscopy) and theoretical study (B3LYP/6-311++G(d,p)) succeeded in assigning the predominant solution state structure of 1a.     

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.     

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.