Propenyl Ether Research Articles

Synthesis, characterization, and reactivity of half-sandwich Ru(II) complexes containing phosphine, arsine, stibine, and bismutine ligands

The synthesis and some reactions of the Ru(II) and Ru(IV) half-sandwich complexes [RuCp(EPh 3)(CH 3CN) 2] + (E=P, As, Sb, Bi) and [RuCp(EPh 3)(η 3-C 3H 5)Br] + have been investigated. The chemistry of this class of compounds is characterized by a competitive coordination of EPh 3 either via a RuE or a η 6-arene bond, where the latter is favored when the former is weaker, that is in going down the series. Thus in the case of Bi, the starting material [RuCp(CH 3CN) 3] + does not react with BiPh 3 to give [RuCp(BiPh 3)(CH 3CN) 2] + but instead gives only the η 6-arene species [RuCp(η 6-PhBiPh 2)] + and [(RuCp) 2(μ-η 6,η 6-Ph 2BiPh)] 2+. Similarly, the EPh 3 ligand can be replaced by an aromatic solvent or an arene substrate. Thus, the catalytic performance of [RuCp(EPh 3)(CH 3CN) 2] + for the isomerization of allyl-phenyl ethers to the corresponding 1-propenyl ethers is best with E=P, while the conversion drops significantly using the As and Sb derivatives. By the same token, only [RuCp(PPh 3)(CH 3CN) 2] + is stable in a non-aromatic solvent, whereas both [RuCp(AsPh 3)(CH 3CN) 2] + and [RuCp(SbPh 3)(CH 3CN) 2] + rearrange upon warming to [RuCp(η 6-PhEPh 2)] + and related compounds. In addition, the potential of [RuCp(EPh 3)(CH 3CN) 2] + as precatalysts for the transfer hydrogenation of acetophenone and cyclohexanone has been investigated. Again aromatic substrates are clearly less suited than non-aromatic ones due to facile η 6-arene coordination leading to catalyst's deactivation.

Cationic photoinitiated copolymerization of 1-propenyl–vinyl ether systems

A kinetic investigation of the photoinitiated cationic copolymerization of 1-propenyl ethers with vinyl ethers monomers was performed by using FT-IR and 1 H-NMR analysis. FT-IR results, obtained in bulk, indicate a higher reactivity of the vinyl ether with respect to the 1-propenyl ether double bond. 1 H-NMR analysis, in CDCl 3 solution, confirms these results which agree with the literature data concerning monofunctional systems. The properties of the UV cured copolymerization products are investigated by DMTA analysis and discussed on the basis of the kinetic investigation results.

Cationic ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-β-D-glucopyranose as a convenient synthesis of dextran

For the convenient synthesis of (1→6)-α-D-glucopyranan, i. e., dextran (4), ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-β-D-glucopyranose (1) has been carried out using BF3·OEt2. With a ratio of [BF3·OEt2]/[1] = 0.5 at 0 °C for 140 h, the yield and Mn of the obtained polymer are 84.0% and 21 700, respectively. The polymer consists of (1→6)-α-linked 2,3,4-tri-O-allyl-D-glucopyranose (2) which is similar to the results for the cationic ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-methyl-β-D-glucopyranose and 1,6-anhydro-2,3,4-tri-O-ethyl-β-D-glucopyranose. Polymer 2 was isomerized using tris(triphenylphosphine)-chlororhodium as the catalyst in toluene/ethanol/water to yield polymeric 2,3,4-tri-O-propenyl-(1→6)-α-D-glucopyranan (3). Deprotection of the propenyl ether linkage of 3 was then performed using hydrochloric acid in acetone to give 4.

Photoinduced and Thermally Induced Cationic Polymerizations Using Dialkylphenacylsulfonium Salts

A study of the photoinitiated and thermally initiated cationic polymerizations of several monomer systems using dialkylphenacylsulfonium salt (DPS) photoinitiators bearing different alkyl chains and anions has been conducted. DPS compounds are capable of photoinitiating the cationic polymerization of a wide variety of epoxy and vinyl ether monomers directly on irradiation with UV light or by using visible light irradiation in the presence of photosensitizers. Kinetic studies show that DPS photoinitiators compare favorably with respect to their reactivity to diaryliodonium and triarylsulfonium salt photoinitiators in the polymerization of epoxides. The photopolymerizations of vinyl and 1-propenyl ethers display a marked induction period consistent with termination of the growing chains by reaction with the photogenerated ylides. Preliminary studies have demonstrated that DPS can also be employed as thermal initiators for the cationic ring-opening polymerization of epoxides at moderate temperatures.

Living cationic polymerization ofn-butyl propenyl ether

Cationic polymerization of n-butyl propenyl ether (BuPE; CH3CH CHOBu, cis/trans = 64/36) was examined with the HCl–IBVE (isobutyl vinyl ether) adduct/ZnCl2 initiating system at −15 ∼ −78 °C in nonpolar (hexane, toluene) and polar (dichloromethane) solvents, specifically focusing on the feasibility of its living polymerization. In contrast to alkyl vinyl ethers, the living nature of the growing species in the BuPE polymerization was sensitive to polymerization temperature and solvent. For example, living cationic polymerization of IBVE can be achieved even at 0 °C with HCl–IBVE/ZnCl2, whereas for BuPE whose β-methyl group may cause steric hindrance ideal living polymerization occurred only at −78 °C. Another interesting feature of this polymerization is that the polymerization rate in hexane is as large as in dichloromethane, much larger than in toluene. A new method in determining the ratio of the living growing ends to the deactivated ones was developed with a devised monomer-addition experiments, in which IBVE that can be polymerized in a living fashion below 0 °C was added to the almost completely polymerized solution of BuPE. The amount of the deactivated chain ends became small in hexane even at −40 °C in contrast to other solvents. Thus hexane turned out an excellent solvent for living cationic polymerization of BuPE. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 229–236, 2000

Regioselective Synthesis and Diels−Alder Reaction of 3,4-Dimethylpenta-1,3-diene. Conformational Study of Bicyclic Adducts Structures by 1H NMR (NOESY, ASIS) and Molecular Modeling (MM2, AM1, RHF, and DFT)

A three-step, regioselective synthesis of 3,4-dimethylpenta-1,3-diene 1 has been developed. The condensation of acetone diethylacetal with ethyl propenyl ether yielded, after hydrolysis of the resulting triethoxy adduct 10, 2,3-dimethyl-2-butenal 7. Wittig reaction of 7 with methylenetriphenylphosphorane afforded desired diene 1 in 31% overall yield, easily scalable to the 10 g level. Diels−Alder reaction of 1 with maleic anhydride in benzene was known to afford a 50:50 mixture of “normal” (2) and “rearranged” (3) adducts. In THF as solvent, 2 has been reproducibly obtained in over 90% yield as a 98:2 mixture with 3. 1H NMR spectroscopy (NOESY, ASIS) and molecular modeling (MM2, AM1, ab initio) have been used jointly to determine the conformation of 2 and 3. All are consistent with a folded structure of “rearranged” 3. On the other hand, only RHF/6-31G* and B3LYP/6-31G* ab initio models were in agreement with NMR spectroscopy for an extended conformation of adduct 2. In this case, neither MM2 nor AM1 models gave results consistent with NMR: discrepancies as high as 30° were noted for some dihedrals between these models and ab initio ones.

SYNTHESIS OF ALKYL AND ARYL 1-PROPENYL ETHER MONOMERS: A NEW APPROACH

A new, convenient synthesis of alkyl and aryl 1-propenyl ether monomers in good to excellent yields has been developed. Alkyl and aryl allyl ethers can be smoothly isomerized to the desired 1-propenyl ethers by refluxing in a basic ethanolic solution containing pentacarbonyliron as a catalyst. A simplified two-step, one-pot procedure has also been developed which consists of combining an alcohol with allyl bromide in the presence of base and then adding pentacarbonyliron to isomerize the in-situ generated allyl ether to directly give the 1-propenyl ether. Good yields of alkyl 1-propenyl ethers were obtained using this process. Factors affecting the isomerization reaction were investigated and a mechanism was proposed.

The synthesis and cationic photopolymerization of monomers based on dicyclopentadiene

Several new epoxide monomers based on dicyclopentadiene (DCPD) were prepared using straightforward reaction chemistry. Those monomer-bearing groups in addition to the epoxy moiety, which can stabilize free radicals, display a pronounced acceleration of the rate of cationic ring-opening polymerization in the presence of diaryliodonium salt photoinitiators. Mechanistic studies conducted with the aid of model compounds have shown that the apparent rate acceleration is due to the free radical chain-induced decomposition of the photoinitiator. One of the chain carriers in this reaction involves a monomer-derived free radical. Also prepared was dicyclopentadiene monomer (V) bearing polymerizable epoxide and 1-propenyl ether groups in the same molecule. The functional groups in V appear to undergo independent vinyl and epoxide ring-opening polymerization.

The synthesis and cationic photopolymerization of monomers based on dicyclopentadiene

Several new epoxide monomers based on dicyclopentadiene (DCPD) were prepared using straightforward reaction chemistry. Those monomer-bearing groups in addition to the epoxy moiety, which can stabilize free radicals, display a pronounced acceleration of the rate of cationic ring-opening polymerization in the presence of diaryliodonium salt photoinitiators. Mechanistic studies conducted with the aid of model compounds have shown that the apparent rate acceleration is due to the free radical chain-induced decomposition of the photoinitiator. One of the chain carriers in this reaction involves a monomer-derived free radical. Also prepared was dicyclopentadiene monomer (V) bearing polymerizable epoxide and 1-propenyl ether groups in the same molecule. The functional groups in V appear to undergo independent vinyl and epoxide ring-opening polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3427–3440, 1999

Photoinitiated cationic oligomerization of aryl 1-propenyl ethers

A series of aryl 1-propenyl ethers (ArPE) were prepared by the isomerization of the corresponding allyl aryl ethers (AArE) and used for photoinduced cationic polymerization studies. Attempted polymerization reactions using diaryliodonium salts as photoinitiators generally resulted in low yields of oligomers. Further studies revealed that these compounds have much lower reactivity in cationic vinyl polymerization as compared to their alkyl analogues. Moreover, side reactions resulting from chain transfer due to Friedel-Crafts alkylations take place and compete with vinyl polymerization. These side reactions are responsible for the low molecular weights observed in the cationic photopolymerization of aryl 1-propenyl ether monomers.

Synthesis and photochemical reaction of novelp-alkylcalix[n]arene derivatives containing cationically polymerizable groups

New photoreactive p-methylcalix[6]arene (MCA) derivatives containing cationically polymerizable groups such as propargyl ether (calixarene 1), allyl ether (calixarene 2), and ethoxy vinyl ether (calixarene 3) groups were synthesized with 80, 74, and 84% yields by the substitution reaction of MCA with propargyl bromide, allyl bromide, and 2-chloroethyl vinyl ether (CEVE), respectively, in the presence of either potassium hydroxide or sodium hydride by using tetrabutylammonium bromide (TBAB) as a phase transfer catalyst (PTC). The p-tert-butylcalix[8]arene (BCA) derivative containing ethoxy vinyl ether groups (calixarene 4) was also synthesized in 83% yield by the substitution reaction of BCA with CEVE by using sodium hydride as a base and TBAB as a PTC. The MCA derivative containing 1-propenyl ether groups (calixarene 5) was synthesized in 80% yield by the isomerization of calixarene 2, which contained allyl ether groups, by using potassium tert-buthoxide as a catalyst. The photochemical reactions of carixarene 1, 3, 4, 5, and 6 were examined with certain photoacid generators in the film state. In this reaction system, calixarene 3 containing ethoxy vinyl ether groups showed the highest photochemical reactivity when bis-[4-(diphenylsulfonio)phenyl]sulfide bis(hexafluorophosphate) (DPSP) was used as the catalyst. On the other hand, calixarene 1 containing propargyl ether groups had the highest photochemical reactivity when 4-morpholino-2,5-dibuthoxybenzenediazonium hexafluorophosphate (MDBZ) was used as the catalyst. It was also found that the prepared carixarene derivatives containing cationically polymerizable groups such as propargyl, allyl, vinyl, and also 1-propenyl ethers have good thermal stability. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1805–1814, 1999

Synthesis and cationic photopolymerization of monomers based on nopol

Starting with nopol [(R)-(−)-2-(2′-hydroxyethyl)-6,6-dimethyl-8-oxatricyclo[3.1.1.12,3]octane, I] as a substrate, two new, interesting monomers, allyl nopol ether epoxide III and nopol 1-propenyl ether epoxide IV, were prepared. The photoinitiated cationic polymerizations of these two monomers as well as several other model compounds were studied using real-time infrared spectroscopy. Surprisingly, the rates of epoxide ring-opening polymerization of both monomers were enhanced as compared to those of the model compounds. Two different mechanisms which involve the free radical induced decomposition of the diaryliodonium salt photoinitiator were proposed to explain the rate acceleration effects. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1199–1209, 1999

Tandem Cycloaddition Chemistry of Nitroalkenes: Probing the Remarkable Stereochemical Influence of the Lewis Acid.

The influence of several Lewis acids on the stereochemical course of the [4 + 2] cycloaddition of nitroalkene 1 and chiral, nonracemic propenyl ether 8 has been examined. All of the Lewis acids examined favored ul relative diastereoselection ("exo" approach); TiCl(4), TiBr(3)(Oi-Pr), SnCl(4), and ATPh were the most selective. Within the titanium-based Lewis acids, it was found that increasing the halide-to-alkoxide ratio increased the degree of ul (relative) selectivity, as did switching from chloride to bromide. The internal diastereoselectivity was also dependent on the Lewis acid; most titanium isopropoxide-halides (bromide and chloride) and SnCl(4) were highly selective for (1,3-lk) approach, with the selectivity increasing with increasing halide content. Two aluminum-based Lewis acids (MAPh and ATPh) were selective for the opposite sense of internal diastereoselection. The high lk (relative) diastereoselectivity observed only with TiCl(2)(Oi-Pr)(2) is proposed to arise either from Coulombic stabilization of an endo approach or precomplexation of the vinyl ether to the Lewis acid. The switch in internal diastereoselectivity seen in the exo manifold is thought to arise from subtle changes in the steric nature of the Lewis acid-nitroalkene complex.

The Reaction of Unsaturated Aliphatic Oxygenates with Ozone

The reaction of ozone with unsaturated aliphatic oxygenates has been studied at ambient T (287–297 K) and p = 1 atm. of air (RH = 55 ± 10%) with sufficient cyclohexane added to scavenge the hydroxyl radical. Reaction rate constants, in units of 10-18 cm3 molecule-1 s-1, are 10.7 ± 1.4 for methyl trans-3-methoxy acrylate, 63.7 ± 9.9 for 4-hexen-3-one (predominantly the trans isomer), 125 ± 17 for trans-4-methoxy-3-buten-2-one, ≥148 ± 13 for cis-4-heptenal, ≥439 ± 37 for 3- methyl-2-buten-1-ol and ≥585 ± 132 for (cis + trans)-ethyl 1-propenyl ether. The influence of the oxygen-containing substituents on reactivity toward ozone is examined. Unsaturated ethers react with ozone faster than their alkene structural homologues; the reverse is observed for unsaturated esters and unsaturated carbonyls. Major reaction products have been identified by liquid chromatography with ultraviolet detection (LC-UV), particle beam-mass spectrometry (PB- MS) and gas chromatography-mass spectrometry (GC-MS) and are methyl formate and methyl glyoxylate from methyl trans-3-methoxy acrylate, acetaldehyde and 2-oxobutanal from 4-hexen-3-one, propanal and succinic dialdehyde from cis-4-heptenal, hydroxyacetaldehyde and acetone from 3-methyl-2-buten-1-ol, and ethyl formate and acetaldehyde from (cis + trans)-ethyl 1-propenyl ether. PB-MS and GC- MS were also employed to identify new reaction products and to confirm the structure of products tentatively identified in a previous study of the reaction of ozone with five unsaturated oxygenates (Grosjean and Grosjean, 1997a): formic acid and methyl glyoxylate from methyl acrylate, formic acid and formic acetic anhydride from vinyl acetate, 2-oxoethyl acetate and 3-oxopropyl acetate from cis-3-hexenyl acetate, ethyl formate and formic acid from ethyl vinyl ether, and methyl formate from trans-4-methoxy-3- buten-2-one. The nature and formation yields of the reaction products are consistent with (and supportive of) the reaction mechanism: O3 + R1R2C=CR3X → α(R1COR2 + R3C(X)OO) + (1 - α)(R3COX + R1C(R2)OO), where R1, R2 and R3 = H or alkyl, X is the oxygen-containing substituent, R1COR2 and R3COX are the primary products and R1C(R2)OO and R3C(X)OO are the carbonyl oxide biradicals. The variations of the coefficient α, which ranges from 0.25 to 0.61, are discussed in terms of the number and nature of alkyl and oxygen-containing substituents. Subsequent reactions of the alkyl-substituted biradicals R1C(R2)OO and of the biradicals R3C(X)OO that bear the oxygen-containing substituent are discussed. For the biradical CH3CHOO, the ratio ka/kb for the competing pathways of rearrangement to acetic acid (CH3CHOO → CH3C(O)OH, reaction (a) and formation of an unsaturated hydroperoxide (CH3CHOO → CH2=CH(OOH), reaction (b) is 99.9%) and comparable to that for formaldehyde (98.4%) for formic acetic anhydride and for difunctional oxygenated compounds. Uptake in water impingers was lower (19–78%) for monofunctional aldehydes and ketones.

Novel Hybrid Monomers Bearing Cycloaliphatic Epoxy and 1-Propenyl Ether Groups

The synthesis of a novel series of hybrid monomers containing cationically polymerizable cycloaliphatic epoxide and 1-propenyl ether functional groups in the same molecule has been conducted. Detailed structure−reactivity studies of the diaryliodonium salt-induced cationic photopolymerizations of these monomers indicate that the rate of epoxide ring-opening polymerization is markedly enhanced by the presence of the 1-propenyl ether group. At the same time, the polymerization of the 1-propenyl ether groups in such hybrid monomers is retarded. A mechanism involving the free-radical-induced decomposition of the photoinitiator has been proposed which serves to amplify the rate of the photoinitiated cationic epoxide ring-opening polymerization.

Preparation of Tailor-Made Multifunctional Propenyl Ethers by Radical Copolymerization of 2-(1-Propenyl)oxyethyl Methacrylate

A new approach for preparation of multifunctional polymers with pendant vinyl ethers was investigated. In particular, 2-(1-propenyl)oxyethyl methacrylate, a new ambifunctional monomer combining easy radical polymerization and a fast cationically cross-linkable group, was evaluated. Hence, the physical characteristics of copolymers were controlled by the selection of comonomers. Cross-linking kinetics as a function of temperature and concentration of the acid-generating species were monitored quantitatively by FT-IR spectroscopy. Through the use of DSC measurements, the onset for cationic polymerization was determined. It was demonstrated that both 9-fluorenylideneimino-p-toluenesulfonate and diphenyliodonium triflate could be used as efficient thermally initiating cross-linking agents.

Free Radical Induced Acceleration of Cationic Photopolymerization

Two new monomers based on α-terpineol were prepared, allyl α−terpineol ether epoxide (III) and 1-propenyl ether α-terpineol epoxide (IV). The photoinitiated cationic polymerizations of these two monomers as well as two model compounds, 1-propenyl α-terpineol ether and methyl α-terpineol ether epoxide, were studied using real-time infrared spectroscopy. Surprisingly, the rates of epoxide ring-opening polymerization of both monomers were greatly enhanced as compared to the model compounds. At the same time, the rate of polymerization of the 1-propenyl ether groups in IV was depressed. Two different mechanisms which involve the free radical induced decomposition of the diaryliodonium salt photoinitiator were proposed to explain the rate acceleration effects.

Solvent Effects on Carbocation−Nucleophile Combination Reactions: A Comparison of π-Nucleophilicity in Aqueous and Organic Solvents

The following selectivities are reported for partitioning of the α-(N,N-dimethylthiocarbamoyl)-4-methoxybenzyl carbocation 1+ between nucleophilic addition of π-nucleophiles and a solvent of 50:50 (v:v) acetonitrile/water at 25 °C (nucleophile, kNu/ks): pyrrole, 23 M-1; 2-methoxythiophene, ≈2 M-1. No nucleophile adducts (<2% of total products) were detected from the reaction of this carbocation in the same solvent containing the following carbon nucleophiles: thiophene (0.10 M), furan (0.10 M), ethyl 1-propenyl ether (0.10 M), amd 1-cyclohexenyl trimethylsilyl ether (0.01 M). These results show that only π-nucleophiles with Mayr nucleophilicity parameters greater than N ≈ 6 are sufficiently reactive to compete with nucleophilic aqueous solvents for addition to 1+, and they provide support for a simple relationship between the Ritchie N+ scale of nucleophilicity in water and the Mayr N scale of nucleophilicity in weakly polar nonnucleophilic solvents.2,3 Our data require a large effective molarity for th...

Asymmetric Total Synthesis of Callystatin A: Asymmetric Aldol Additions with Titanium Enolates of Acyloxazolidinethiones

A number of highly cytotoxic polyketides, including the anguinomycins,1 leptofuranins,2 leptomycin,3 and kazusamycin,4 having similar gross chemical structures have been isolated from Streptomyces strains. Recently, a structurally related polyketide, callystatin A 1, was isolated from the marine sponge, Callyspongia truncata, in the Nagasaki Prefecture.5 Callystatin A shows remarkable in vitro cytotoxicity (IC50 ) 0.01 ng/mL) against KB cells. The relative and absolute stereostructure of callystatin A was established by a combination of spectroscopic methods and chemical synthesis.5-7 The limited quantities of callystatin A available from natural sources, as well as the possibility for carrying out syntheses and structure elucidation of the related antitumor antibiotics, prompted us to pursue a total synthesis of callystatin A.8 Here we disclose the asymmetric total synthesis of (-)-callystatin A exploiting our recently developed asymmetric aldol protocol with chlorotitanium enolates of acyl oxazolidinethiones.9 Strategically, E-selective olefination10 of aldehyde 2 (Scheme 1) with the phosphorane derived from tributylphosphonium salt 3 appeared to offer the most convergent assembly of callystatin A. Aldehyde 2 representing C1 to C12 would be constructed from a similar olefination between the masked pyranone aldehyde 4 (Scheme 2) and phosphonium salt 5 (Scheme 3). The C13 to C22 propionate fragment 3 was to be constructed through consecutive asymmetric aldol additions9 employing acyl oxazolidinethione 6 (Scheme 4). The synthesis of aldehyde 4 began with S-glycidol 7 as illustrated in Scheme 2. Protection of S-glycidol as its TBDPS ether followed by copper-catalyzed epoxide opening with vinylmagnesium bromide provided the alcohol 8 in 85% overall yield. Conversion of the secondary alcohol to the isopropoxy propenyl ether provided a mixed acetal which was exposed to the Grubbs catalyst11 to effect ring-closing metathesis to dihydropyran 9 (71% overall). Removal of the TBPDS protecting group with n-Bu4-

Base Catalyzed Isomerizations of Allyl Ethers to 1-Propenyl Ethers Using Mixed Alkali Systems

ABSTRACT Allyl ethers were successfully isomerized to 1-propeny1 ethers using the strong inorganic bases CsOH or KOH/CaO as catalysts in the absence of solvents. Both catalyst systems required elevated temperatures and, of the two systems, KOH/CaO is more efficient and cost effective. Using KOH/CaO and conducting reactions at ∼200°C for 2–3 hours gave up to 93% isomerization to the 1-propenyl ether. Under similar conditions, no isomerization occurred when either KOH or CaO were used alone. Attempted isomerizations of 2-butenyl ethers to 1-butenyl ethers, were unsuccessful due to a side reaction that results in the elimination of butadiene from the starting material under the basic conditions. †Current address: Department of Chemistry, Vassar College, Poughkeepsie, NY 12601.