- Synthesis of 3-alkylseleno-2-cylcobutenone via [2+2] cycloaddition reaction of alkyneselenolate with diphenylketene
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3-Alkylseleno-2-cyclobutenones were synthesized by reaction of alkyneselenolate with diphenylketene via [2+2] cycloaddition. The complete structure of the 2-cyclobutenone was determined by X-ray diffraction.
- Koketsu, Mamoru,Kanoh, Masanori,Ishihara, Hideharu
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- Concerted wolff rearrangement in two simple acyclic diazocarbonyl compounds
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The photochemistry of two simple acyclic diazo carbonyl compounds, azibenzil and diazoacetone, were studied using the tools of ultrafast time-resolved spectroscopy. In the former case, UV-vis detection allows observation of an absorption band of singlet benzoylphenylcarbene, decaying with a 740 ± 150 ps time-constant in acetonitrile. IR detection shows that the ketene product of Wolff rearrangement (～2100 cm-1) is formed by two parallel pathways: a stepwise mechanism with carbene intermediacy with a slow rise time-constant of 660 ± 100 ps, and directly in the diazo excited state as confirmed by the immediate formation of an IR band of a nascent hot ketene species. Photolysis (270 nm) of diazoacetone in chloroform leads mainly to the ketene species through a concerted process, consistent with the predominance of the syn conformation in the diazoacetone electronic ground state and a zero quantum yield of the internal conversion process.
- Burdzinski, Gotard,Zhang, Yunlong,Wang, Jin,Platz, Matthew S.
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- Synthesis and time resolved infrared analysis of photochemical oxiranyl carbene and diphenyl ketene precursors
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Synthesis of a nonnitrogenous phenanthrene-based precursor of oxiranyl carbene yielded a photochemical source for diphenyl ketene after an in situ intramolecular rearrangement. The initial carbene precursor targeted rearranged from a putative spiro-oxiranyl intermediate to a cyclobutanone. Photolysis of the phenanthrene–cyclobutanone generated an infrared signal centered at 2100?cm?1consistent with diphenyl ketene formation. Time-resolved infrared spectroscopy followed the reaction progress and measured bimolecular rate constants (kobs?=?9.1?×?106?M?1?s?1; butyl amine) consistent with diphenyl ketene formation. Quenching experiments combined with Stern–Volmer kinetics suggests a radical pathway is likely involved in the formation of diphenyl ketene from the phenanthrene-based precursor. The generality of the rearrangement is also discussed.
- Tippmann, Eric M.,Curtis, Ryan
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- Synthesis of γ-Lactams by Formal Cycloadditions with Ketenes
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The synthesis of γ-lactams is reported by a formal (3+2) cycloaddition between readily available ketenes and aziridines or a one-pot formal (2+1+2) cycloaddition using imines as aziridine precursors. The method is practical, is scalable, and affords high yields. It also offers a high level of regio- and diastereoselectivity on a wide range of substrates as well as a high stereoselectivity in the case of enantiopure aziridines.
- Viceriat, Audrey,Marchand, Isabelle,Carret, Sébastien,Poisson, Jean-Fran?ois
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supporting information
p. 2449 - 2454
(2021/04/05)
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- Coordination behaviors of diphenylketene adsorbed in the nanocages of zeolite NaY and AgY
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We investigated in detail how polar cumulene molecules like diphenylketene were accommodated in faujasite zeolite pores based on 13C CP/MAS and DD/MAS NMR analyses as well as quantum chemical calculations after adsorbing the molecule into the zeolite NaY or AgY having “hard” sodium ions or “soft” silver ions. Since the diphenylketene has such a specific structure that a carbonyl group (a hard base) is accumulated by a carbon-carbon double bond (a soft π base), which is conjugated with two benzene rings (soft π bases), it is possible for the diphenylketene to adopt multicoordination modes to different metal ions in the zeolite. Compared with the coordination modes of benzophenone and 1,1-diphenylethene adsorbed in the NaY and AgY, those of diphenylketene were identified, and specific coordination behaviors in the zeolite’s supercages were classified depending on the hard or soft metal characters: The C=O and phenyl coordination modes to Na+ in NaY prevail, while the C=C and phenyl coordination to Ag+ in AgY is favored. We also unveiled the difference in the molecular mobility depending on the types of cations in the zeolite by comparing the 13C CP/MAS and DD/MAS NMR spectra.
- Shibata, Shintaro,Masui, Yoichi,Onaka, Makoto
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supporting information
p. 663 - 670
(2020/12/29)
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- A photoinduced Wolff rearrangement/Pd-catalyzed [3+2] cycloaddition sequence: An unexpected route to tetrahydrofurans
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A novel sequential reaction that combines a visible light-induced Wolff rearrangement of α-diazoketones and a Pd-catalyzed [3+2] cycloaddition of vinyl cyclopropanes with the resulting ketenes is described in this work. Selective O-allylic alkylation was observed over C-allylic alkylation, which unexpectedly led to a series of highly functionalized tetrahydrofurans with high efficiency (20 examples, 58-99% yields).
- Liu, Jie,Li, Miao-Miao,Qu, Bao-Le,Lu, Liang-Qiu,Xiao, Wen-Jing
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supporting information
p. 2031 - 2034
(2019/02/19)
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- Thermal [2+2]-cycloadditions of diphenylketene with aryl- and hetaryl-substituted thioketones
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The reaction of diphenylketene (1) with aryl- and hetaryl-substituted thioketones (2) gave the corresponding 3,3,4,4-tetraarylthietan-2-ones (3) in good yields. Remarkably, the reactions with bis-hetaryl-substituted thioketones occurred significantly faster compared with those involving the bis-aryl-substituted thioketones. The structure of compound 3c has been established by X-ray crystallography.
- Mlosto, Grzegorz,Urbaniak, Katarzyna,Szychowska, Anna,Linden, Anthony,Heimgartner, Heinz
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p. 529 - 539
(2015/03/04)
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- Ketenes from N-(2-Pyridyl)amides
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Methoxycarbonylketene 4a, methoxycarbonyl(methyl)ketene 4b, chloroketene 4c, cyanoketene 4d, diphenylketene 4e, and 2-pyridylketene 4f have been generated by flash vacuum thermolysis of the corresponding 2-pyridylacetamide derivatives 3a-f and isolated in Ar matrices for FT-IR spectroscopic characterisation. The N-(2-pyridyl)-2-pyridylacetamide 3f yielded 2-pyridyl isocyanate in addition to 2-pyridylketene.
- Plüg, Carsten,Kanaani, Hussein,Wentrup, Curt
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p. 687 - 692
(2015/04/27)
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- Synthesis, electronic structure and reactivity of bis(imino)pyridine iron carbene complexes: Evidence for a carbene radical
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The reactivity of the disubstituted diazoalkane, N2CPh 2 with a family of bis(imino)pyridine iron dinitrogen complexes was examined. For the most sterically protected member of the series, ( iPrPDI)Fe(N2)2 (iPrPDI = 2,6-(2,6-iPr2C6H3NCMe) 2C5H3N), an S = 1 iron diazoalkane complex was obtained and structurally characterized. Reducing the size of the 2,6-aryl substituents to ethyl or methyl groups resulted in isolation of bis(imino)pyridine iron carbene complexes. Magnetic measurements established S = 1 ground states, demonstrating rare examples of iron carbenes in a weak ligand field. Electronic structure determination using metrical parameters from X-ray diffraction as well as Moessbauer, XAS and computational data established high-spin iron(ii) compounds engaged in antiferromagnetic coupling with redox-active bis(imino)pyridine and carbene radicals. The Royal Society of Chemistry 2014.
- Russell, Sarah K.,Hoyt, Jordan M.,Bart, Suzanne C.,Milsmann, Carsten,Stieber, S. Chantal E.,Semproni, Scott P.,Debeer, Serena,Chirik, Paul J.
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p. 1168 - 1174
(2014/03/21)
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- Lewis acid-promoted ketene-alkene [2 + 2] cycloadditions
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Described are the first examples of ketene-alkene [2 + 2] cycloadditions promoted by Lewis acids. Notable features of this method include (1) substantial rate acceleration relative to traditional thermal reactions, (2) good diastereoselectivities and yields for the formation of the cyclobutanone products, and (3) inverse diastereoselectivity compared with related thermal cycloadditions for many examples. These studies not only provide access to synthetically versatile cyclobutanones that cannot be prepared by traditional thermal cycloadditions but also address important mechanistic questions regarding ketene-alkene [2 + 2] cycloaddition reactions.
- Rasik, Christopher M.,Brown, M. Kevin
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supporting information
p. 1673 - 1676
(2013/04/10)
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- Mechanistic insight into the Staudinger reaction catalyzed by N-heterocyclic carbenes
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Four zwitterions were prepared by treating 1,3-dimesitylimidazolin-2- ylidene (SIMes) or 1,3-dimesitylimidazol-2-ylidene (IMes) with either N-tosyl benzaldimine or diphenylketene. They were isolated in high yields and characterized by IR and NMR spectroscopy. The molecular structures of three of them were determined by using X-ray crystallography and their thermal stability was monitored by using thermogravimetric analysis. The imidazol(in)ium-2-amides were rather labile white solids that did not show any tendency to tautomerize into the corresponding 1,2,2-triaminoethene derivatives. They displayed a mediocre catalytic activity in the Staudinger reaction of N-tosyl benzaldimine with diphenylketene. In contrast, the imidazol(in)ium-2-enolates were orange-red crystalline materials that remained stable over extended periods of time. Despite their greater stability, these zwitterions turned out to be efficient promoters for the model cycloaddition under scrutiny. As a matter of fact, their catalytic activity matched those recorded with the free carbenes. Altogether, these results provide strong experimental insight into the mechanism of the Staudinger reaction catalyzed by N-heterocyclic carbenes. They also highlight the superior catalytic activity of the imidazole-based carbene IMes compared with its saturated analogue SIMes in the reaction under consideration. Catalysts caught in the act: The N-heterocyclic carbenes 1,3-dimesitylimidazolin-2- ylidene (SIMes) and 1,3-dimesitylimidazol-2-ylidene (IMes) react with N-tosyl benzaldimine or diphenylketene to afford the corresponding zwitterions in high yields (see scheme). The molecular structures of three of them were determined by X-ray crystallography and their thermal stability was monitored by thermogravimetric analysis. The NHC×ketene betaines were found to be key intermediates for the Staudinger reaction catalyzed by NHCs. Copyright
- Hans, Morgan,Wouters, Johan,Demonceau, Albert,Delaude, Lionel
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supporting information
p. 9668 - 9676
(2013/07/26)
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- Carbene radicals in cobalt(II)-porphyrin-catalysed carbene carbonylation reactions; A catalytic approach to ketenes
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One-pot radicals: Cobalt(III)-carbene radicals, generated by metallo-radical activation of diazo compounds and N-tosylhydrazone sodium salts with cobalt(II) complexes of porphyrins, readily undergo radical addition to carbon monoxide, allowing the catalytic production of ketenes. These ketenes subsequently react with various amines, alcohols and imines in one-pot tandem transformations to produce differently substituted amides, esters and β-lactams in good isolated yields. Copyright
- Paul, Nanda D.,Chirila, Andrei,Lu, Hongjian,Zhang, X. Peter,Debruin, Bas
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supporting information
p. 12953 - 12958
(2013/10/01)
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- Multistep one-pot wittig/nazarov reaction for construction of cyclopentenone with diazo compounds and acid chlorides
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A facile multistep one-pot synthesis of single or fused cyclopentenones has been developed. The sequence involves a transition metalcatalyzed ylide formation/Wittig Olefination/Nazarov Cyclization.
- Cao, Peng,Sun, Xiu-Li,Zhu, Ben-Hu,Shen, Qi,Xie, Zuowei,Tang, Yong
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supporting information; experimental part
p. 3048 - 3051
(2009/12/27)
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- Ketene-forming elimination reactions from aryl phenylacetates promoted by R2NH in MeCN: Effects of base-solvent and β-phenyl group
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Elimination reactions of C6H5C(R)HCO 2C6H3-2-X-4-NO2 [R = H (1), Ph (2), X = H (a), Cl (b), NO2 (c)] promoted by R2NH in MeCN have been studied kinetically. The reactions are second-order and exhibit Broensted β = 0.46-0.89 and |β1g| = 0.37-0.76 and an E2 mechanism is evident. When the base-solvent was changed from R 2NH/R2NH2+-70 mol% MeCN(aq) to R2NH-MeCN, β and |β1g| values remained nearly the same within experimental error. For eliminations from 1 and 2, β and |β1g| values were nearly identical, although the rate was retarded by the β-Ph group. Noteworthy is the relative insensitivity of the ketene-forming transition state to the base-solvent and β-R group variation. Copyright
- Pyun, Sang Yong,Seok, Hyoun Jung,Kim, Ju Chang,Kim, Hwan Myung,Cho, Bong Rae
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p. 685 - 689
(2008/03/12)
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- SYNTHESIS OF STERICALLY HINDERED SECONDARY AMINOETHER ALCOHOLS
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Severely sterically hindered secondary aminoether alcohols are prepared by reacting organic carboxylic, organic carboxylic acid halides, acid anhydrides or a ketene with an alkyl, alkaryl or alkylhalo sulfonate to yield a sulfonic. Carboxylic anhydride compound which is then reacted with a dioxane to cleave the ring of the dioxane, yielding a cleavage product which cleavage product is then aminated with an alkylamine and hydrolyzed with base to yield the severely sterically hindered secondary aminoether alcohol.
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Page/Page column 23
(2008/06/13)
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- Pericyclic reaction of ketenes with cascade reaction products of pyridine N-oxides and dipolarophiles. X-ray structures of the adducts and formation mechanism.
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The structures of the adducts derived from the reactions of substituted ketenes with dihydropyridine derivatives have been clarified by single crystal X-ray analyses and the formation mechanism is discussed on the basis of the reaction-path calculations by semiempirical and density functional theory (DFT) molecular orbital methods.
- Oiso, Shigeru,Eto, Masashi,Yoshitake, Yasuyuki,Harano, Kazunobu
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p. 1068 - 1074
(2007/10/03)
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- The development of the first catalyzed reaction of ketenes and imines: Catalytic, asymmetric synthesis of β-lactams
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We report practical methodology for the catalytic, asymmetric synthesis of β-lactams resulting from the development of a catalyzed reaction of ketenes (or their derived zwitterionic enolates) and imines. The products of these asymmetric reactions can serve as precursors to a number of enzyme inhibitors and drug candidates as well as valuable synthetic intermediates. We present a detailed study of the mechanism of the β-lactam forming reaction with proton sponge as the stoichiometric base, including kinetics and isotopic labeling studies. Stereochemical models based on molecular mechanics (MM) calculations are also presented to account for the observed stereoregular sense of induction in our reactions and to provide a guidepost for the design of other catalyst systems.
- Taggi, Andrew E.,Hafez, Ahmed M.,Wack, Harald,Young, Brandon,Ferraris, Dana,Lectka, Thomas
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p. 6626 - 6635
(2007/10/03)
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- Anodic oxidation of benzil hydrazones in the presence of halide ions
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Benzil hydrazones were subjected to electrolytic oxidation in MeOH containing halide ion source, such as KI and KBr. The results show that the reaction products were dependent on both the electrolytes and the substituents. In the presence of KI, benzoylphenyldiazomethanes were obtained, whereas in the presence of KBr, benzil dimethyl acetals were obtained.
- Okimoto, Mitsuhiro,Takahashi, Yukio
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p. 2059 - 2060
(2007/10/03)
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- Synthesis, structure, and reactions of a three-coordinate nickel-carbene complex, {1,2-bis(di-tert-butylphosphino)ethane}Ni=CPh2
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The three-coordinate nickel-carbene complex (dtbpe)NiCPh2 (3) was prepared from the thermolysis of the diphenyldiazoalkane complex (dtbpe)Ni(N,N-:η2-N2CPh2) (2) (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane). Complex 3 was structurally characterized by single-crystal X-ray diffraction methods (Ni-C = 1.836(2) A). Complex 3 reacts with 2 equiv of CO2 to afford (dtbpe)Ni{OC(O)CPh2C(O)O} (4), with diphenylketene to give (dtbpe)Ni{OC(CPh2)CPh2} (5), with excess CO to transfer the carbene fragment and generate diphenylketene and (dtbpe)Ni(CO)2 (6), with sulfur dioxide to give the metallasulfone (dtbpe)Ni{C,S:η2-S(O)2CPh2} (7), and with the Bronsted acid [HNMe2Ph][B(C6F5)4] to give the alkyl cation [(dtbpe)Ni(CHPh2)][B(C6F5)4] (8). Complexes 4, 5, and 7 have also been characterized by single-crystal X-ray diffraction methods. Copyright
- Mindiola, Daniel J.,Hillhouse, Gregory L.
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p. 9976 - 9977
(2007/10/03)
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- Tandem [4+2] cycloaddition versus electrocyclisation reactions of 1-aryl-2-phenyl-5-alkyl/aryl-1,3-diazapenta-1,3,4-trienes in aza-Wittig reactions of N′-aryl-N-(triphenylphosphoranlidene) benzenecarboximidamides with ketenes
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1-Aryl-2-phenyl-5-alkyl/aryl-1,3-diazapenta-1,3,4-triene 3 generated in situ aza-Wittig reactions of N′-aryl-N-(triphenylphosphoranylidene)carboximidamides 1 which are shown to undergo selective [4+2] cycloaddition and electrocyclisation reactions leading to the formation of novel pyrimidinone derivatives 5 and quinazoline derivatives 7 with monosubstituted ketenes and diphenylketene, respectively.
- Jayakumar,Kumar, Vipan,Mahajan, Mohinder P.
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p. 2235 - 2237
(2007/10/03)
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- Carbenerhodium complexes of the half-sandwich-type: Synthesis, substitution, and addition reactions
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A series of carbenerhodium(I) complexes of the general composition [(η5-C5H5)Rh(=CRR′)(L)] (2a-2i) with R = R′ = aryl and L = SbiPr3 or PR3 has been prepared from the square-planar precursors trans-[RhCl(=CRR′)(L)2] and NaC5H5 in excellent yields. Reaction of the triisopropylstibane derivative 2a, which contains a rather labile Rh-Sb bond, with CO, PMe3, and CNR (R = Me, CH2Ph, tBu) leads to the displacement of the SbiPr3 ligand and affords the substitution products [(η5-C5H5)Rh-(=CPh2)(L)]. (3-7). In contrast, treatment of the triisopropylphosphane compound 2c with CO and CNtBu leads to the cleavage of the Rh=CPh2 bond and gives besides [(η5-C5H5)Rh(PiPr3)(L)] (10, 12) by metal-assisted C-C coupling diphenylketene Ph2C=C=O (11) or the corresponding imine Ph2C=C=NtBu (13). While the reaction of 2a, c with C2H4 yields [(η5-C5H5)Rh(C2H4) (L)] (14, 15) and the trisubstituted olefin Ph2C=CHCH3 (16), treatment of 2a, c with RN3 leads to the cleavage of both the Rh-EiPr3 and Rh=CPh2 bonds and gives the chelate complexes [(η5-C5H5)-Rh(κ2-RNNNNR )] (19, 20). The substitution products 3 (L = CO) and 4 (L = PMe3) react with an equimolar amount of sulfur or selenium by addition of the chalcogen to the Rh=CPh2 bond to generate the complexes [(η5-C5H5) Rh-(κ2-ECPh2)(L)] (21-24) with thio- or selenobenzophenone as ligand. Similarly, treatment of 3 with CuCl affords the unusual 1:2 adduct [(η5-C5H5)(CO)Rh-(μ-CPh2) (CuCl)2] (25), which reacts with NaC5H5 to form [(η5-C5H5)(CO)Rh(μ-CPh2)Cu (η5-C5H5)] (26). The molecular structures of 3 and 22 have been determined by X-ray crystallography.
- Werner, Helmut,Schwab, Peter,Bleuel, Elke,Mahr, Norbert,Windmueller, Bettina,Wolf, Justin
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p. 4461 - 4470
(2007/10/03)
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- Spectroscopy and absolute reactivity of ketenes in acetonitrile studied by laser flash photolysis with time-resolved infrared detection
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Laser flash photolysis with time-resolved infrared detection of transients (LFP-TRIR) has been used to study the IR spectroscopy and reactivity of a number of substituted ketenes, prepared by the 308-nm photolysis of α-diazocarbonyl precursors in acetonitrile solution at room temperature. The correlation of the experimental ketene asymmetric stretching frequency to the Swain-Lupton field (F) and resonance (R) effect substituent parameters was unsatisfactory, whereas the correlation to the inductive substituent parameter (σ1) of Charton gave excellent results. This suggests that the asymmetric stretching frequency of substituted ketenes depends mainly on the inductive (i.e., field) effect of the substituents. The mechanism and kinetics of the reactions of these ketenes with various amines in acetonitrile were also studied. An intermediate species identified as either zwitterionic ylide or amide enol formed in the nucleophilic addition of the secondary amine to the C(α) of the ketene is observed by TRIR. The decay of this species is assisted by the amine and is concomitant with the formation of an amide, the final product of the reaction. Our kinetic data on ketene amine reactions show a general trend, indicating a much higher reactivity (ca. 3 orders of magnitude difference in the corresponding rate constants) of secondary amines compared with that of tertiary amines. Secondary diethylamine shows reactivity similar to those observed for primary amines, while secondary piperidine seems to be, in general, somewhat more reactive. The observed trend is rationalized in terms of the steric effects exerted by both amine and ketene substituents. Our data on para-substituted phenyl ketenes provide support for the negative charge development on the ketene moiety in the transition state, with electron-withdrawing substituents accelerating and electron-releasing substituents slowing down the addition reaction.
- Wagner, Brian D.,Arnold, Bradley R.,Brown, Gerald S.,Lusztyk, Janusz
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p. 1827 - 1834
(2007/10/03)
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- New ventures in the construction of complex heterocycles: Synthesis of morphine and hasubanan alkaloids
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Synthetic approaches to morphine and hasubanan alkaloids involving novel reactions for the formation of their dihydrobenzofuran, piperidine and pyrrolidine ring, respectively, are described. The importance of conformational constraints for the success of these reactions is demonstrated. The syntheses of new dioxepanes, diazepanes, dithiocanes, triazenes and dioxonanes are also reported.
- Trauner, Dirk,Porth, Stefanie,Opatz, Till,Bats, Jan W.,Giester, Gerald,Mulzer, Johann
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p. 653 - 664
(2007/10/03)
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- A new family of carbenerhodium(i) complexes: Ligand variation as the key to success
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A synthetic methodology to obtain square-planar carbenerhodium(I) complexes of the general composition trans-[RhCl(=CRR')(L)2] where L is a tertiary phosphane, arsane, or stibane has been developed. The starting material trans-[RhCl(C2H4)(SbiPr3)2] (3) reacts with diazoalkanes RR'CN2 [RR' = Ph2, Ph(C6H4X), (C6H4X)2, Ph(CF3), C12H8] under mild conditions to give the compounds trans-[RhCl(=CRR')(SbiPr3)'2] (4-11) almost quantitatively. On treatment of 3 with EtO2CCHN2 and PhC(N2)C(O)R, the olefin rhodium and diazoalkanerhodium compounds trans[RhCl{(E)-C2H2(CO2Et)2}(SbiPr3)2] (12) and trans-[RhCl{N2C(R)C(O)Ph}(Sb-iPr3)2] (13, 14) are obtained instead of carbene complexes. Displacement of the SbiPr3 ligands in 4 (R=R'=Ph) by PiPr3, PiPr2Ph, PiPrPh2, PPh3, PPh2Me, AsiPr3, and SbEt3 leads to the corresponding carbene complexes trans-[RhCl-(=CPh2)(L)2] (15-21) in high yields. The results of the X-ray crystal structure analyses of 4 and 15 (L = PiPr3) illustrate that the different donor-acceptor properties of SbiPr3 and PiPr3 have little influence on the Rh-C bond length. The reactions of 4 and 15 with CO and CNtBu afford, by metal-assisted C-C coupling, diphenylketene Ph2C=C=O (23) and the corresponding imine Ph2C=C=NtBu (26). On treatment of 4 and 15 with ethene, however, two different olefinic products, 3,3-diphenyl-1-propene (31) and 1,1-diphenyl-1-propene (32), are formed. Compound 15 reacts with KBr, NaOPh, and NaC5H5 by substitution of the chloride to give trans-[RhBr(=CPh2)-(PiPr3)2] (33), trans-[Rh(OPh)(=CPh2)-(PiPr3)2] (34) and [C5H5Rh(=CPh2)-(PiPr3)] (35), and with HCl by oxidative addition toyield [RhCl2(CHPh2)-(PiPr3)2] (36).
- Werner, Helmut,Schwab, Peter,Bleuel, Elke,Mahr, Norbert,Steinert, Paul,Wolf, Justin
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p. 1375 - 1384
(2007/10/03)
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- Azido acids in a novel method of solid-phase peptide synthesis
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Azido acids were produced from α-branched acids by α-bromination with NBS followed by substitution with sodium azide and the products were used in a novel method of solid-phase synthesis. The azido acids were transformed into the highly activated acid chlorides and used synthesis of extremely hindered peptides containing up to four successive diphenyl glycine or Aib residues. By reaction of the genetically encoded amino acids with TfN3 and then SOCl2 they were transformed into α-azido acid chlorides used in solid-phase peptide synthesis without racemization.
- Meldal, Morten,Juliano, Maria A.,Jansson, Anita M.
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p. 2531 - 2534
(2007/10/03)
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- Dihydrofurans from α-diazoketones due to facile ring opening - Cyclization of donor-acceptor cyclopropane intermediates
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A series of α-diazoketones, 8, 25, 28, 31, and 34, have been synthesized and their reaction with ethyl vinyl ether examined under various reaction conditions. In the presence of metal salts (Rh2(OAc)4, Pd(OAc)2, CuCl) the ethoxydihydrofurans 12, 37, 39, 41, and 43 are produced. Sensitized irradiation of the α-diazoketone 8 afforded the dihydrofuran 12 plus cyclobutanone 7, while direct photolysis of α-diazoketones 8, 25, 28, 31, and 34 gave the cyclobutanones 7, 38, 40, 42, and 44, respectively. A sample of the cyclopropylketone 45 was isolated from the rhodium(II) acetate mediated reaction of 34 and its facile rearrangement to dihydrofuran 43 demonstrated. Collectively, these results indicate that the initial product from the reaction of an α-diazoketone with an electron-rich alkene such as ethyl vinyl ether is a cyclopropylketone. The donnor-acceptor substitution pattern of this intermediate results in spontaneous rearrangement to a dihydrofuran. Thus a direct dipolar cycloaddition mechanism is not involved when α-diazoketones react with enol ethers under metal-mediated conditions. Instead, these reactions follow a cyclopropanation rearrangement or, more accurately, cyclopropanation - ring opening - cyclization pathway.
- Lund, Elizabeth A.,Kennedy, Isaac A.,Fallis, Alex G.
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p. 2401 - 2412
(2007/10/03)
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- Electrosynthesis of 2-benzhydrylidene-4,4-diphenyl-[1,3]oxathiolan-5-one: The reaction pathway
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The pathway for the electrochemical formation of 2-benzhydrylidene-4,4-diphenyl-[1,3]oxathiolan-5-one (2), in dichloromethane tetraethylammonium bromide on graphite cathode is proposed. It involves reaction between electrogenerated diphenylketene (3), 2-bromo-2,2-diphenylacetyl bromide (1) and sulfide anion. The latter is formed from H2S generated in the anodic compartment and electrogenerated bases.
- Lozano, Jose I.,Barba, Fructuoso
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p. 1259 - 1266
(2007/10/03)
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- PHOSPHORUS PENTACHLORIDE REACTIONS WITH CONJUGATED CARBONYL COMPOUNDS AND CONJUGATED OLEFINS
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Phosphorus pentachloride was reacted with conjugated aromatic and carbonyl compounds.The conjugated aromatic compounds were cis and trans stilbene, and the carbonyl compounds were diphenylketene and 2,3,4,5-tetraphenylcyclopentadienone.Two solvents used for these reactions were 1,1,2,2-tetrachlorethane and methylene chloride.Phosphorus pentachloride can dissociate into phosphorus trichloride and chlorine and our results indicated this was the reaction mechanism for phosphorus pentachloride reacting with 2,3,4,5-tetraphenylcyclopentadienone.With stilbene, cis andtrans, the mechanism with phosphorus pentachloride was the sp3d2 octahedral complex mechanism.With diphenylketene the mechanism was the dissociation of phosphorus pentachloride into the phosphorus tetrachloro action and the phosphorus hexachloro anion.Key words: Phosphorus pentachloride, stilbene, diphenylketene, and 2,3,4,5-tetraphenylcyclopentadienone.
- Duty, Robert C.,Farley, Thomas H.
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p. 271 - 280
(2007/10/02)
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- Novel ketene formation by reactions of acid chlorides with low-valent platinum complexes
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Pt(CO)n(PPh3)4-n (n = 0-2) reacts with Ph2CHCOCl under CO to afford diphenylketene and trans-PtHCl(PPh3)2.For this reaction, the rate law is zero order in the platinum complex, first order in Ph2CHCOCl, and first order in free PPh3.A primary isotope effect (kH/kD = 4.5) was observed in the reaction of Ph2CDCOCl.A mechanism is proposed which involves the rate-determining enolization of Ph2CHCOCl by PPh3 followed by fast abstraction of HCl by a platinum(0) complex.
- Ishii, Youichi,Kobayashi, Yoshihiro,Iwasaki, Masakazu,Hidai, Masanobu
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p. 133 - 140
(2007/10/02)
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- Hel Photoelectron Studies of Unstable Ketenes: Mono- and Di-phenylketenes, and their Gas-phase Conformations
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Hel photoelectron spectra are reported for the semistable mono- and di-phenylketene molecules generated in high yield by in situ metal dehalogenation reactions of the appropriate chlorophenyl-substituted acid chlorides.The photoelectron results can be interpreted through a simple perturbation approach, and in conjunction with semiempirical MNDO and AM1 calculations provide gas-phase structural evidence for a planar ?-conjugated monophenylketene molecule, and a non-planar diphenylketene species in which both phenyl groups are rotated, in a conrotatory fashion, some 30-40 deg out of the >C=C=O ? system.The limitations of the MNDO method and the greater reliability of AM1 for the assessment of the relative energies of rotational conformers is discussed.HAM/3 calculations are in excellent agreement with the experimental ionisation potentials.
- Sammynaiken, Ramaswami,Westwood, Nicholas P. C.
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p. 1987 - 1992
(2007/10/02)
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- Reactions of Carboxylic Acids with "Phosphonium Anhydrides"
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General considerations are outlined for a reagent to extract oxygen from organic molecules by an equivalent of dehydration.Reagents, (R3P+)2O, 2OTf-, were created for the purpose and subjected to a preliminary study.They were found to convert carboxylic acids readily and rapidly to anhydrides, esters, amides, amidines, benzimidazoles, and cyclic aryl ketones in good yields.
- Hendrickson, James B.,Hussoin, Md. Sajjat
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p. 1144 - 1149
(2007/10/02)
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- Triplet Ground-State Benzoylphenylmethylene and Its Quintet Ground-State Triplet-Triplet Radical Pair
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Photolysis of crystalline azibenzil powder at 77 K and λ >/= 345 nm generates a complex ESR spectrum consisting of four components, namely a strong triplet, a weak triplet, a quintet, and a doublet.The strong triplet has been previously assigned to ground-state benzoylphenylmethylene and the quintet to the ground state of a radical pair formed between two triplet benzoylphenylmethylenes.On the basis of the similar values exhibited by the zero-field splitting parameters, the strong and weak triplet signals are assigned here to the s-Z and s-E isomers of the ground state of benzoylphenylmethylene, respectively.The s-Z conformer is more abundant and less stable than the s-E, and on annealing, the decay of both signals follows first-order kinetics.Above 90 K the quintet radical pair also decays with first-order kinetics to yield a new triplet diradical, which is stable at T 120 K but disappears with first-order kinetics above 120 K.The Arrhenius parameters have been determined for all decay reactions and utilized in their mechanistic interpretation.The carrier of the structureless, broad doublet signal observed appears to be generated from the secondary photolysis of the tiplet benzoylphenylmethylene.The assignment of the quintet spectrum to a radical pair is also supported by the absence of this spectrum in the photolysate of dilute azibenzil solutions in glassy matrices.Under such conditions, in addition to the spectrum of benzoylphenylmethylene and its doublet photolysis products, a new triplet diradical appears wiht a kinetics of formation suggesting that it is formed by the decay of the quintet.However, its identity has not been established.
- Murai, H.,Safarik, I.,Torres, M.,Strausz, O. P.
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p. 1025 - 1032
(2007/10/02)
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- Substituted ketene elimination from acid chlorides induced by ruthenium(0) compounds
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The compound Ru(CO)2(triphos) (triphos=MeC(CH2PPh2)3) reacts with a number of acid chlorides RR'CHCOCl to form Cl and the corresponding substituted ketenes RR'CCO.A quantitative study of the reaction of Ph2CHCOCl shows that Ph2CCO is formed in a 1:1 stoichiometry.The compound Ru(CO)3(PPh3)2 also reacts with Ph2CHCOCl forming Ph2CCO and the unstable hydride Cl, the chemistry of which is also reported.
- Singh, Shanti,Baird, Michael C.
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p. 255 - 260
(2007/10/02)
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- Insertion of Ketene and Diphenylketene to the Pnictogen-Heteroatom Bonds
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Ketene and diphenylketene insert across the heteroatom-metal bond of amino-, alkoxy-, and alkylthio-pnictogens, R3-nMXn, to give the corresponding α-metallated acetamides, esters, and thioesters, R3-nM(CH2COX)n and R3-nM(CPh2COX)n (M=As, Sb, Bi; X=NR2, OR, SR; n=1,3), respectively.
- Ando, Fumio,Kohmura, Yoshihiko,Koketsu, Jugo
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p. 1564 - 1566
(2007/10/02)
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- Hydration reactivity of ketenes generated by flash photolysis
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The ketenes n-BuCH=C=O, PhCH=C=O, and Ph2C=C=O have been generated by flash photolysis and their reactivities toward water, including acid and base catalysis, have been measured in wholly aqueous media by ultraviolet spectrophotometry.The phenyl group electronically enhances the reactivity of ketenes relative to n-butyl toward water and hydroxide, but retards reaction with protic acids.The presence of bulky groups, including phenyls, on each side in the ketene plane sterically retards nucleophilic attack.The reactions are interpreted as involving in-plane attack by nucleophilic water or hydroxide in the natural and base-induced reactions, and electrophilic protonation perpendicular to the ketene plane for the acid-catalyzed reaction.
- Allen, Annette D.,Kresge, A. Jerry,Schepp, Norman P.,Tidwell, Thomas T.
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p. 1719 - 1723
(2007/10/02)
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- Capture of Electron-Deficient Species with Aryl Halides. New Syntheses of Hypervalent Iodonium Ylides
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We have demonstrated the aryl iodide capture of β-diketocarbenes, generated from the diazo compound by using rhodium(II) acetate, under very mild conditions.This is a useful general preparative method for iodonium ylides under non-hydroxylic conditions.The termal, catalytic, and photochemical decompositions of various azides in the presence of aryl iodides were carried out.With highly reactive nitrenes, intramolecular rearrangement takes precedence over capture.In the case of p-tuloenesulfonyl azide, thermolysis in the presence of aryl iodides requires conditions under which the iminoiodane is itself decomposed.The capture of oxene by iodobenzene is discussed.The application of these capture processes is discussed as a synthetic route to hypervalent ylides as well as on the basis of mechanism.
- Moriarty, Robert M.,Bailey, B. R. III,Prakash, Om,Prakash, Indra
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p. 1375 - 1378
(2007/10/02)
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- Keten. Part 19. Reactions of 2,4,6-Trimethylbenzonitrile N-Oxide with Ketens
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Diphenylketen, t-butylcyanoketen, and dimethylketen react with the title nitrile oxide to form 1:1 adducts shown to have the oxazolinone structures (5); keten, t-butylethoxycarbonylketen, and phenyl isocyanate fail to react.The nitrile oxide is deoxygenated by diphenylketen and dimethylketen; in the latter case a new type of deoxygenation process occurs forming the unsaturated ketone (11) and thence the isoxazoline (8).
- Evans, Andrew R.,Taylor, Giles A.
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p. 979 - 983
(2007/10/02)
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- -CYCLOADDITION OF DITHIOBENZOIC ESTERS TO DIPHENYLKETENE
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Dithiobenzoic esters and diphenylketene react by a mechanism of -cycloaddition with the formation of 4-alkylthio-2-thietanones.During thermolysis and electron impact the products readilly undergo both the retro reaction with the formation of the initial structures and cyclodecomposition with the elimination of carbon sulfoxide.
- Drozd, V. N.,Popova, O. A.
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p. 946 - 949
(2007/10/02)
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- Azomethine Imines by Reaction of Diphenylketene with Azodicarboxylates
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The reaction of diphenylketene with azodicarboxylates yields azomethine imines 4 which show 1,3-dipolaric reactivity: addition of diphenylketene yields the 2:1 adduct 8, addition of phenylisocyanate productes 7, and dimerization leads to 5.
- Fahr, Egon,Buettner, Ehrfried,Keil, Karl-Heinz,Markert, Juergen,Scheckenbach, Franz,et al.
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p. 1433 - 1444
(2007/10/02)
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- Keten. Part 17. Addition Reactions of Ketens with N-Phenyl Nitrones
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The N-phenyl nitrones (1a), (4b), and (15) react with ketens in two totally different ways.Triphenylnitrone (4b) forms oxidolones (6) whereas (1a) and (15) form oxazolidinones (2) and (17).The differences appear to be caused by steric interactions in (1a) and (15) which distort the nitrone function and prevent the N-phenyl group adopting the conformation necessary for the oxindole-forming pathway.
- Hafiz, Mushtag,Taylor, Giles A.
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p. 1700 - 1705
(2007/10/02)
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- Redox-Photosensitized Reactions. 5. Redox-Photosensitized Ring Cleavage of 1,1a,2,2a-Tetrahydro-7H-cyclobutindene Derivatives: Mechanism and Structure-Reactivity Relationship
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The mechanistic aspects of the redox-photosensitized chain cycloreversion of trans,syn-indene dimer 1 have been investigated in detail.The ? complex of 1 with the cation radical of phenanthrene (and selected other aromatic hydrocarbons) that is generated by photochemical electron transfer with p-dicyanobenzene has been shown to be a key intermediate by way of which the cycloreversion of 1 rapidly occurs without the formation of its cation radical; the rate constant for the cycloreversion has been determined to be 1*109 s-1.Redox photosensitization has been applied to the other related compounds and it has been found that the cyclobutanes which can undergo redox-photosensitized ring cleavage possess the phenyl group at C2.The importance of through-bond interactions between the two ?-electron system is discussed.
- Majima, Tetsuro,Pac, Chyongjin,Sakurai, Hiroshi
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p. 5265 - 5273
(2007/10/02)
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- Acylation of aromatic substrates with ketenes. An example of vinyl oxocation reactivity.
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Acylations of aromatic substrates with ketenes involve the reactivity of species similar to vinyl cations.Resonance stabilization of ketene-aluminum chloride complexes seems to make these complexes less reactive than corresponding vinyl cations.The kinetic isotope effect of the reaction with dimethylketene and benzene is 1.06, compatible with vinylcation cases, but not with acylation with CH3COBF4 types of electrophiles.Substrate specificity was determined from k (toluene)/k (benzene) values.It was 47.2 for dimethylketene and 173.7 for diphenylketene.The diphenylketene-aluminum chloride complex could be isolated.
- Fountain, K.R.,Heinze, Pamela,Sherwood, Mark,Maddex, Dave,Gerhardt, Greg
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p. 1198 - 1205
(2007/10/02)
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- Acylation of aromatic substrates with ketenes. II. Hammett-Brown studies on substituted aromatic compounds
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Competition reactions using dimethylketene (DMK) - aluminium chloride complexes on a variety of substituted benzene derivatives gave partial rate factors.The logs of these Pfx values when plotted versus ?+ values gave two line segments of ρ = -6.59 for less active substrates, and ρ = -0.92 for more active substrates.Similar results were found for diphenylketene (ρ = -9.47 and -1.07).These results were rationalized by analogy to vinyl cation alkylations.A pair of ? complexes (outher then inner) occur between initial approach of the reagent and final, product-determining ?-complex formation.In one of these complexes the C=C bond of the ketene complex may be able to back-bond in a manner similar to that found in inorganic complexes of CO and metals.
- Fountain, K. R.,Heinze, Pamela,Maddex, Dave,Gerhardt, Greg,John, Paul
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p. 1939 - 1946
(2007/10/02)
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