Wittig-like Reaction Research Articles

Metallophthalocyanine catalyzed olefination of aldehydes

The Wittig reaction to synthesize olefins is a very attractive method in organic synthesis. Recently, this methodology has been achieved utilizing simple metal catalysts and diazo compounds in addition to a phosphine and an aldehyde. The following work investigates the use of a variety of metallophthalocyanines (MPc’s) to catalyze Wittig-like reactions from ethyldiazoacetate. We also examine the influence of substitution on the aromatic ring of the aldehyde as well as various phosphines, arsines and antimony complexes. We have been able to exclusively synthesize the trans-olefins in excellent yields in short periods of time (1 h).

Synthesis and Optical Spectroscopy of Oligo(1,6-heptadiynes) with a Single Basic Structure Prepared through Adamantylimido-Based Molybdenum Wittig and Metathesis Chemistry

Linear oligoenes of 1,6-heptadiynes (derived from dialkyl dipropargylmalonates) with a single basic structure and up to 23 conjugated double bonds were synthesized through Wittig-like reactions between bimetallic Mo-alkylidene compounds and aldehyde-capped oligoenes. The relatively rigid and isomerically pure oligoenes have structures with alternating cis,trans conjugated double bonds in which the cis double bond is part of a cyclopentene ring. Molecular weights have been confirmed through MALDI-MS measurements of samples purified by HPLC. Optical spectra of the purified samples show significant vibronic resolution, even in room temperature samples, and are remarkably similar to those of simple polyenes and carotenoids. Therefore, a systematic investigation of the dependence of the allowed electronic transition energies (electronic origins) on conjugation lengths has become possible. Studies of seven allowed transitions for molecules with 5-23 double bonds (= N) indicate asymptotic convergence (with approximately a 1/N dependence) to a common long polyene limit at approximately 16,000 cm(-1). The convergence of these electronic transitions agrees with theoretical treatments of polyene excited-state energies and is consistent with the absorption spectra of analogous diethyl dipropargylmalonate polymers (1/N approximately 0).

Synthesis of Oligoenes that Contain up to 15 Double Bonds from 1,6-Heptadiynes

This paper reports the synthesis of polyene oligomers ("oligoenes") that contain up to 15 double bonds that are identical to the "all five-membered ring" species formed through cyclopolymerization of diisopropyldipropargylmalonate. The oligoenes contain an isopropylidene unit at each end. The isolated oligoenes range from the "dimer" (a pentaene, (E)-di-1,2-[1-(2-methyl-propenyl)-4,4-di-iso-propyl-carboxy-cyclopent-1-enyl]-ethene (3b2)) to the "heptamer" (3b7, a pentadecaene). Oligoenes 3b2, 3b3, 3b4, 3b5, and 3b7 were prepared through Wittig-like reactions between aldehydes and the appropriate monometallic Mo alkylidene or bimetallic Mo bisalkylidene species whose alkylidene is derived from an identical five-membered ring monomeric unit. Compounds 3b2, 3b4, and 3b6 were prepared through McMurry coupling reactions of aldehydes. A representative aldehyde (the "monomeric" aldehyde) is diisopropyl-3-formyl-4-(2-methylprop-1-enyl)cyclopent-3-ene-1,1-dicarboxylate (2b), McMurry coupling of which yields 3b2. A heptaene that contains a six-membered ring in the central unit also was prepared in a Wittig-like reaction involving a bimetallic Mo alkylidene; this species is a model for oligoenes that contain both six-membered and five-membered rings. X-ray structures of two bimetallic species that are employed in the synthesis of the oligoenes are reported.

Synthesis and Evaluation of Imidazolylmethylenetetrahydronaphthalenes and Imidazolylmethyleneindanes: Potent Inhibitors of Aldosterone Synthase

Elevated plasma aldosterone levels play a detrimental role in certain forms of congestive heart failure and myocardial fibrosis. We proposed aldosterone synthase (CYP11B2) as a novel target for the treatment of these diseases. In this study, the synthesis and biological evaluation of substituted E- and Z-imidazolylmethylenetetrahydronaphthalenes and E- and Z-imidazolylmethyleneindanes (compounds 1a,b-9a,b) is described. The compounds were prepared by a Wittig-like reaction. They were tested for activity using bovine CYP11B and human CYP11B2 expressed in fission yeast and V79 MZh cells. Selectivity was determined toward human CYP11B1, CYP19, and CYP17. Especially in the case of CYP11B1 (steroid 11beta-hydroxylase), selectivity is a crucial issue, since sequence homology between this enzyme and the target enzyme is very high (93%). On the basis of the X-ray structure of human CYP2C9, a protein model of CYP11B2 was developed and docking experiments with the title compounds were performed. The biological results revealed highly potent inhibitors of CYP11B2 (IC(50) = 4-93 nM). The Z-isomers usually were more active than the corresponding E-isomers. Different inhibitory profiles could be observed: rather selective inhibitors of CYP11B1, dual inhibitors of both enzymes, and rather selective inhibitors of CYP11B2. The chloro derivative 8b was found to be a highly potent CYP11B2 inhibitor (IC(50) = 4 nM) showing a 5-fold selectivity for CYP11B1 (IC(50) = 20 nM). This compound could be an interesting lead for further optimization as a therapeutic agent. It also could be used as well as the CYP11B1 selective compounds as a pharmacological tool.

Synthesis of a Silica-Based Heterogeneous Second Generation Grubbs Catalyst

The synthesis of a second generation Grubbs catalyst immobilized onto non-porous silica is described. For this purpose, a polymerizable cationic NHC precursor, 1,3-bis(1-mesityl)-4-{[(bicyclo[2.2.1]hept-5-en-2-ylcarbonyl)oxy]methyl}-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate (5) was prepared and characterized by X-ray analysis. Oligomers were prepared therefrom using both the well-defined Schrock initiator Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)[OCMe(CF3)2]2 and the first generation Grubbs catalyst Cl2Ru(CHPh)(PCy3)2. Ru-initiated oligomerizations were terminated with ethyl vinyl ether, Mo-initiated oligomerizations were terminated by addition of (EtO)3SiCH2CH2CH2NCO. (EtO)3Si-terminated oligomers obtained by the Wittig-like reaction between the Mo-containing oligomer and the isocyanate were used for the immobilization of the NHC-precursor containing oligomers on non-porous silica. Both oligomerizations were characterized by quantitative consumption of the corresponding initiator. This allowed the controlled synthesis of oligomers via stoichiometry. Using both non-porous and porous silica, degrees of derivatization of 0.04 and 0.02 mmol, respectively, of cationic NHC precursor/g silica were obtained. These precursors were converted into the corresponding NHC's by standard procedures and used for the generation of a heterogeneous second-generation Grubbs catalyst. Ruthenium loadings of 5.3 and 1.3 μmol/g, corresponding to 0.5 and 0.1 weight-% of catalyst were realized. Additionally, coating techniques were applied, where C18-derivatized silica-60 was loaded with oligo-5. Conversion into the corresponding heterogeneous catalyst revealed 4.1 μmol/g, corresponding to 0.4 weight-% of catalyst. All supported catalysts prepared by this approach were successfully used in RCM in slurry type reactions.

Block Copolymers by Transformation of Living Ring-Opening Metathesis Polymerization into Controlled/“Living” Atom Transfer Radical Polymerization

A general method of transformation of living ring-opening metathesis polymerization (ROMP) into controlled/“living” atom transfer radical polymerization (ATRP) is reported for the preparation of block copolymers. For example, the macroinitiators PNB−C6H4−CH2Br (Mn = 30 520, Mw/Mn = 1.09) or PDCPD−C6H4−CH2Br (Mn = 12 100, Mw/Mn = 1.24) were prepared by ROMP of norbornene (NB) or dicyclopentadiene (DCPD) and subsequent Wittig-like reactions with p-(bromomethyl)benzaldehyde. These compounds were used as efficient macroinitiators for homogeneous controlled/“living” ATRP to prepare block copolymers with styrene (St), PNB-b-PSt (Mn = 110 400, Mw/Mn = 1.06) and PDCPD-b-PSt (Mn = 20 100, Mw/Mn = 1.37), and methyl acrylate (MA), PNB-b-PMA (Mn = 85 100, Mw/Mn = 1.07) and PDCPD-b-PMA (Mn = 25 300, Mw/Mn = 1.47).

Well-defined redox-active polymers and block copolymers prepared by living ring-opening metathesis polymerization

Mo(CH-t-Bu)(NAr)(O-t-Bu){sub 2} (1a) in Thf/0.1 M [n-Bu{sub 4}N]AsF{sub 6} is not oxidized at potentials up to 1.0 V and undergoes a reversible, one electron reduction at -2.16 V vs SCE at a Pt electrode. An analogous intiator containing a ferrocenylmethylidene ligand (1b) can be synthesized by treating 1a with vinylferrocene. Redox-active derivatives of norbornene, containing ferrocene (2) or phenothiazine (3), were prepared and polymerized by 1a or 1b to give living block copolymers containing the ring-opened norborene derivatives. The living polymer was cleaved from the metal in a Wittig-like reaction with pivaldehyde, trimethylsilylbenzaldehyde, or octamethylferrocenecarboxaldehyde. Polydispersities for the longer block copolymers containing up to {approximately}90 monomer units were found to be as low as 1.05 by GPC. In one case the polydispersity of a homopolymer made from the ferrocene-containing monomer was determined by FD-mass spectroscopy to be 1.06. DSC studies suggest that microphase studies of homo and block copolymers showed that the redox centers were electrochemically independent and that all centers exchanged electrons with the electrode. Neutral polymers became insoluble upon oxidation to a polycation, yielding an adsorbed polymer layer on the electrode that could then be cathodically stripped. This oxidative deposition process depended on the electrolyte and the polymermore » molecular weight but also could be controlled by the size of a nonelectroactive block in the block copolymers. Problems resulting from precipitation of the redox polymers could be circumvented by employing normal pulse voltammetry. Polymers containing redox centers in both end groups as well as in the polymer chain itself have been prepared and their nature confirmed in electrochemical studies.« less

Preparation of tert-butyl-capped polyenes containing up to 15 double bonds

7,8-Bis(trifluoromethyl)tricyclo(4.2.2.0{sup 2.5})deca-3,7,9-triene (TCDT) can be ring-opened in a controlled manner by W(CH-t-Bu)(NAr)(O-t-Bu){sub 2} (Ar = 2,6-C{sub 6}H{sub 3}-i-Pr{sub 2}) to give living oligomers from which the metal can be removed in a Wittig-like reaction with pivaldehyde or 4,4-dimethyl-trans-2-pentenal. Mixtures of odd and even polyenes have been analyzed by reversed-phase HPLC methods, and those having as many as 13 double bonds have been isolated by column chromatography on silica gel under dinitrogen at {minus}40{degree}C and characterized by {sup 1}H and {sup 13}C NMR and UV-vis studies. The 17-ene has been observed by HPLC. Polyenes containing more than 17 double bonds are relatively unstable under the reaction and subsequent isolation conditions; those containing between 11 and 15 double bonds decompose thermally progressively more readily. UV-vis and {sup 13}C and {sup 1}H NMR data have been collected and analyzed in detail for the trans(cis,trans){sub x} isomers for x = 1-5 (up to 11 double bonds) and for the odd and even all-trans forms containing up to nine double bonds.

Low polydispersity homopolymers and block copolymers by ring opening of 5,6-dicarbomethoxynorbornene

Abstract : Addition of 50-200 eq of norbornene to Mo(CH Superscript t Bu) (NAr) (O Superscript t Bu)2 yields living polymers, Mo?CH(C5H8)CHxCH Superscript t Bu (NAr)(O Superscript t Bu)2 (55% trans), that are stable for days in the absence of water and oxygen with essentially no isomerization of the double bonds in the chain. Addition of benzaldehyde cleaves off the polymer in a Wittig-like reaction to yield polynorbornenens with polydispersities in the range 1.04-1.11. Analogous reactions involving 50-200 eq of endo, endo-5,6-dicarbomethoxynorbornene yields homopolymers with polydispersities in the range 1.11-1.22. Block copolymers containing 50 eq of endo,endo-5,6-dicarbomethoxynorbornene and 200 eq of norbornene prepared by adding one or the other monomer first are virtually identical (polydispersities 1.06 and 1.09 with M sub n 57200 and 59900, respectively). These results suggest that the molybdenum catalyst will not react significantly with up to 100 eq of ester functionality during the time of a typical polymerization reaction (approx. 15 m at 25 degs.).

Multiple metal-carbon bonds. 41. Wittig-like reactions of tungsten alkylidyne complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMultiple metal-carbon bonds. 41. Wittig-like reactions of tungsten alkylidyne complexesJohn H. Freudenberger and Richard R. SchrockCite this: Organometallics 1986, 5, 2, 398–400Publication Date (Print):February 1, 1986Publication History Published online1 May 2002Published inissue 1 February 1986https://doi.org/10.1021/om00133a041RIGHTS & PERMISSIONSArticle Views513Altmetric-Citations77LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (438 KB) Get e-Alerts Get e-Alerts

Investigations of polymerization and metathesis reactions: Part I: Carbene reactions with polymerization and metathesis catalysts

With a polymerization catalyst, a reduced Phillips catalyst and a Dolgoplosk metathesis catalyst (WCl 6/N 2CHCOOC 2H 5), well-known carbene ligand reactions such as cyclopropanation with alkenes and a Wittig-like reaction with ketones may be used as model reactions. For all these model reactions ethyl diazoacetate (DAAE) has been used as the carbene source. Whereas the reduced Phillips catalyst produced cyclopropanes as the main products, the metathesis catalyst WCl 6/DAAE gave dimers of the carbene ligand in good yield and only poor yields of cyclopropanes. No carbene complex reaction products could be found with the heterogeneous metathesis catalysts WO 3/SiO 2 and W(CO) 6/Al 2O 3 in both model reactions.

ACIDITY AND REACTIVITY OF α-ARYLAZOPHENACYLTRIPHENYLPHOSPHONIUM BROMIDES

Abstract Two series of new compounds, i.e., α-arylazophenacyltriphenylphosphonium bromides 4 and the corresponding ylides 5 were prepared. Both 4 and 5 were found unreactive in Wittig-like reactions, possibly due to the high acidity of 4 and the low basicity of 5. The pKa values of 4 were determined in 80% (vol.) ethanol-water and were found to be correlated by the Hammett equation.

Silicon—carbon multiple-bonded (P Pπ Pπ) intermediates : III. Reactions of thiobenzophenone with thermally generated 1,1-disubstituted 1-silaethenes, [R 2SiCH 2]: evidence for a Pπ Pπ silicon—sulfur double-bonded species

Reactions of [R 2SiCH 2] (R  Me, Ph), generated by thermolysis of the corresponding 1,1-disubstituted silacyclobutane at 611°C, with Ph 2CS are described. A Wittig-like reaction takes place, yielding Ph 2CCH 2 and what are believed to be the first examples of transient [R 2SiS].