Showing papers on "Diazomethane published in 1999"

A Recyclable Ru-Based Metathesis Catalyst

Abstract: A Ru carbene (8, Scheme 2) that contains an internal metal−oxygen chelate is an active metathesis catalyst and is readily obtained by the sequential treatment of Cl2Ru(PPh3)3 with (2-isopropoxyphenyl)diazomethane and PCy3 This Ru-carbene complex offers excellent stability to air and moisture and can be recycled in high yield by silica gel column chromatography The structures of this and related complexes have been unambiguously established by NMR and single-crystal X-ray diffraction studies

Synthesis of Enantiomerically Pure Cyclopropanes from Cyclopropylboronic Acids.

Abstract: A general method for the stereocontrolled synthesis of cyclopropanes is described. Various, highly stable, enantiomerically pure alkenylboronic esters 13 have been conveniently synthesized by the direct hydroboration of alkynes 11 using the new chiral 1,3,2-dioxaborolane 15. The high stability was also demonstrated by the selective deprotection of a tert-butyldimethylsilyl protecting group without hydrolyzing the boronic ester. The diastereoselective cyclopropanation of the olefins was achieved by the palladium(II) acetate catalyzed decomposition of diazomethane. This process was optimized giving cyclopropylboronic esters 20/21 in high yield (89-99%) and with good to excellent diastereomeric ratios (up to 95:5). The diastereomers were separated by means of MPLC and their configurations determined by X-ray crystallography (compound 21c), by transformation to known cyclopropanols, and by correlation of NMR data. Treatment with LiAlH(4) followed by acidic hydrolysis yielded the enantiomerically pure cyclopropylboronic acid 27 for the first time and allowed the nearly quantitative recovery of the chiral auxiliary 3. Different protocols for the Suzuki coupling reaction of compound 27 were investigated.

Application of Reactive Enols in Synthesis: A Versatile, Efficient, and Stereoselective Construction of the Welwitindolinone Carbon Skeleton

Abstract: Recently, efforts to identify biologically important natural products from cyanobacteria resulted in the isolation of several welwitindolinone alkaloids, two of which have been identified as antagonists of the P-glycoprotein P-170 and hence as MDRreversing agents.1 As part of an ongoing synthesis directed toward the most potent congener, N-methylwelwitindolinone C isothiocyanate (1), we developed an efficient synthesis of 3, a key intermediate that contains the complete carbon framework. Herein we report the details of our investigation. From a retrosynthetic perspective we are focusing on a strategy wherein the chloroolefin and sensitive isothiocyanate will arise late in the sequence via interchange of a ketone and hydroxyl moiety, respectively, in intermediate 2 (Scheme 1). To access 2 the approach proceeds through 3 and, in turn, two R-diazo ketones, 4 and 5. The more advanced of these, compound 4, is a versatile intermediate from which several end-game scenarios are being explored. The second, diazo ketone 5, serves as precursor to 4 and enables the use of aryl C-H insertion chemistry in assembling the 3,4-bridged oxindole core from isatin (6). In the forward sense, isatin was found to be an excellent substrate for Wittig homologation with ethyl triphenylphosphoranylidene acetate.2 The derived enoate (7) is produced in high yield and complete selectivity for the illustrated olefin isomer (Scheme 2). Sequential exposure of 7 to isopropyl triphenylphoshorane and MeI results in clean conversion to the corresponding gem-dimethyl cyclopropane 8.3 Saponification of 8 furnishes acid 9 which,4 upon conversion to its acid chloride and treatment with diazomethane produces R-diazo ketone 5. Having established ready access to diazo ketone 5, efforts to prepare 15 via aryl C-H insertion began.5 Initial studies illustrated that if Rh2(TFA)4 is used as catalyst, 5 reacts to produce equimolar amounts of 14 and 15 along with a trace of spirocycle 11. After considerable experimentation it was discovered that the norcaradiene/cycloheptatriene interconversion leading to the undesired byproduct 14 (i.e., 13 f 12) can be suppressed in situ with the mildly Lewis acidic clay, Montmorillonite K10.6 Under these

First Highly Regio- and Diastereoselective [3+2] Cycloaddition of Chiral Nonracemic Alkenyl Fischer Carbene Complexes with Diazomethane Derivatives: Preparation and Synthetic Applications of Enantiomerically Pure Δ2-Pyrazolines

Abstract: Enantiomerically pure orthogonally N,N′-diprotected azaprolines 1 and 2,4-diaminoalcohols 2 are readily accessible by [3+2] cycloaddition of (−)-8-phenylmenthol-derived alkenyl Fischer carbene complexes 3 with diazomethane derivatives.

Disulfonyl diazomethane compounds)

Abstract: Disclosed is a poly(disulfonyl diazomethane) compound as a class of novel compounds represented by the general formula ##STR1## in which the subscript n is 1 to 5, each R is a monovalent hydrocarbon group and Z is a divalent hydrocarbon group. The invention also discloses a chemical-amplification positive-working photoresist composition which comprises the above mentioned poly(disulfonyl diazomethane) compound as the radiation-sensitive acid-generating agent in combination with a film-forming resin capable of being imparted with increased solubility in an aqueous alkaline solution by the interaction with an acid, such as a polyhydroxystyrene resin of which a part of the hydroxyl groups are substituted by acid-dissociable solubility-reducing groups, e.g., tert-butoxycarbonyl groups.

Cycloaddition Reactions of 1-Phenylseleno-2-(p-toluenesulfonyl)ethyne

Abstract: 1-Phenylseleno-2-(p-toluenesulfonyl)ethyne (1) is an effective dienophile and dipolarophile. It underwent facile Diels−Alder reactions with a variety of dienes to afford vicinal sulfone- and selenide-functionalized 1,4-cyclohexadienes. Unexpected regiochemistry that is the opposite of what is obtained with simple acetylenic sulfones was observed with several unsymmetrical dienes containing methyl or methoxy substituents at the 1- or 2-position. Acetylene 1 reacted with (trimethylsilyl)methyl azide, diazomethane, and 2,4,6-trimethylbenzonitrile N-oxide via 1,3-dipolar cycloadditions to afford the corresponding triazole, 1,2-diazole, and isoxazole products. It also underwent an ene reaction with β-pinene that showed anomalous regiochemistry compared to other acetylenic sulfones. The Diels−Alder cycloadducts obtained from the reaction of 1 with 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene were readily converted into the corresponding β-keto sulfones and ketones, thus rendering 1 as the synthetic equival...

The Reaction of Diazomethane Derivatives with the Dielement Compounds R2Al–AlR2 and R2Ga–GaR2 [R = CH(SiMe3)2] – Insertion versus Fragmentation

Abstract: Tetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 reacted with trimethylsilyldiazomethane and bis(trimethylsilyl)diazomethane at room temperature by the insertion of the terminal nitrogen atoms into its aluminium–aluminium bond. As shown by a crystal structure determination, one of the aluminium atoms of each product enhanced its coordination number to four by the interaction with the central nitrogen atom of the C=N–N group, which results in the formation of a three-membered AlN2 heterocycle bearing an exocyclic N=C double bond. The reactions of the corresponding gallium compound (2) containing a gallium–gallium single bond needed more drastic conditions. Mixtures of many unknown products were formed, and only on treatment with trimethylsilyldiazomethane two compounds could be isolated after repeated recrystallization in yields below 10%, which were characterized by crystal structure determinations. One was identified as the trimeric dialkylgallium cyanide (8) with a nine-membered Ga3C3N3 heterocycle, and the other one (9) has a dialkylgallium fragment coordinated by both terminal nitrogen atoms of the chelating ligand NH2–N=C(SiMe3)–NH−. Due to the NMR spectroscopic characterization, 8 seems to be tetrameric in solution with an asymmetric structure containing four different gallium atoms. With this unusual structure, the IR spectrum of tetrameric dimethylgallium cyanide could now completely be interpreted, which was published more than 20 years ago.

Substituent effects on the reactivity of the silicon-carbon double bond. Substituted 1,1-dimethylsilenes from Far-UV laser flash photolysis of α- silylketenes and (trimethylsilyl)diazomethane

Abstract: Photolysis of (trimethylsilyl)-, bis(trimethylsilyl)-, and pentamethyldisilanylketene in hydrocarbon solution in the presence of aliphatic alcohols affords alkoxysilanes from trapping of silene reactive intermediates. The silenes (1,1,2-trimethylsilene, 1,1,2-trimethyl-2-(trimethylsilyl)silene, and 1,1-dimethyl-2-trimethylsilene) can be viewed as the products of [1,2]-methyl or -trimethylsilyl migration in the silyl carbene formed by photodecarbonylation of the ketene, although a competing direct excited-state pathway cannot be ruled out. Far-UV (193 nm) laser flash photolysis of the compounds in hydrocarbon solution affords transients which are formed during the ∼20 ns laser pulse and are assignable to the silenes on the basis of their UV absorption spectra and reactivity toward alcohols. 1,1,2-Trimethylsilene has also been generated by laser flash photolysis of (trimethylsilyl)diazomethane and -diazirine in hexane and acetonitrile solution, and its spectrum and rate constants for reaction with MeOH, MeO...

Synthesis of Mono‐ and Di(oxopyri)porphyrins: A New Approach through Ring Enlargement with Diazomethane

Abstract: A novel approach for porphyrin modification is provided by ring-enlargement reactions. Treatment of dioxochlorins (see scheme) and tetraoxobacteriochlorins with diazomethane results in formation of the corresponding mono- and di(oxopyri)porphyrins.

Effect of β-Substituents on the Regioselectivity of the Diazomethane Ring Expansion of α-Methyl-α-methoxycyclobutanones to Cyclopentanones

Abstract: The ring expansion of 22 differently β-substituted α-methyl-α-methoxycyclobutanones by diazomethane was studied. Migration of the less-substituted α-carbon was favored with the single exception of a very sterically hindered β-benzyloxy β-substituent.

A Novel Class of Conformationally Constrained, Masked Cysteines: Synthesis of 2-Alkyl- and 2-Arylsulfanyl-1-aminocyclopropanecarboxylic Acids.

Abstract: A convenient synthesis of 4-sulfanylmethylene-5(4H)-oxazolones 3 was realized starting from 4-(chloromethylene)oxazolone 1 and mercaptans 2. Oxazolones 3 were used as starting materials for the preparation of unknown 2-sulfanyl-1-aminocyclopropanecarboxylic acid derivatives 5 and7. Oxazolones 3 were cyclopropanated at the exocyclic double bond with diazomethane, giving a mixture of the two (Z)- and (E)-spirocyclopropane oxazolones 4 with good diastereoselectivity. These were then treated with ethanol and DMAP to produce the corresponding carboxylates 5. The trityl derivative 5d was converted into a mixture of diastereoisomeric disulfides 6 using iodine in ethanol solution. Disulfides 6 are convenient synthons for the preparation of 3-sulfanyl-substituted 2,3-methanoamino acids 7.

Poly (disulfonyl diazomethane) compound and positive-working chemical-amplification photoresist composition containing the same

Abstract: Disclosed is a poly(disulfonyl diazomethane) compound as a class of novel compounds represented by the general formula R-SO 2 -C(N 2 )-SO 2  Z-SO 2 -C(N 2 )-SO 2  n R in which the subscript n is 1 to 5, each R is a monovalent hydrocarbon group and Z is a divalent hydrocarbon group. The invention also discloses a chemical-amplification positive-working photoresist composition which comprises the above mentioned poly(disulfonyl diazomethane) compound as the radiation-sensitive acid-generating agent in combination with a film-forming resin capable of being imparted with increased solubility in an aqueous alkaline solution by the interaction with an acid, such as a polyhydroxystyrene resin of which a part of the hydroxyl groups are substituted by acid-dissociable solubility-reducing groups, e.g., tert-butoxycarbonyl groups.

Homologation of alpha-amino acids to beta-amino acids using Fmoc-amino acid pentafluorophenyl esters.

Abstract: The homologation of alpha-amino acids to beta-amino acids by the two-step Arndt-Eister method is achieved by using Fmoc-alpha-amino acid pentafluorophenyl esters for the acylation of diazomethane, synthesizing the key intermediates Fmoc-aminoacyldiazomethanes as crystalline solids in good yields and purity.

Diazomethane Derivatives Bearing Dialkylaluminium or DialkylgalliumSubstituents – The Isomeric Diazomethane and Nitrile Imine Structures Realized by the Different Coordination Behavior of Aluminium and Gallium

Abstract: Lithium trimethylsilyldiazomethanide Li(SiMe3)CN2 reacted with the dialkylaluminium or -gallium halides R2AlCl and R2GaBr [R = CH(SiMe3)2] by the elimination of lithium halide and the formation of the corresponding aluminium or gallium diazo compounds. As shown by a crystal structure determination, the gallium derivative 1 adopts the nitrile imine structure, in which the gallium atom is coordinated by the terminal nitrogen atom of the diazo group. The N–N–C–Si moiety is almost ideally linear with N–N and C–N bond lengths of 125.5 and 115.9 pm on average. In contrast, the diazomethane structure was formed with dialkylaluminium chloride, and the aluminium atom in 2 is attached to the carbon atom of diazomethane. The almost linear N–N–C group (174.1°) has N–N and N–C distances of 120.0 and 126.4 pm, respectively, inverse to that of the gallium derivative. The bonding situations can best be described by the resonance structures R–C≡N+–N−–GaR2 for 1 and R2Al–(R)C=N+=N− for 2. The nitrile imine isomer of the aluminium compound could be detected by NMR spectroscopy as a by-product. Both compounds gave dimers in the solid state, a Ga2N2 four-membered heterocycle was formed of 1, while an eight-membered Al2C2N4 heterocycle resulted with 2.