Vinyl ether 290 Subject

A recently developed application of the Ramberg-Backlund reaction is the synthesis of C-glycosides. The required thioethers can be prepared easily by exchange with a thiol. The application of the Ramberg-Backlund conditions then leads to an exocyclic vinyl ether that can be reduced to the C-nucleoside.95 Entries 3 and 4 in Scheme 10.6 are examples. The vinyl ether group can also be transformed in other ways. In the synthesis of partial structures of the antibiotic altromycin, the vinyl ether product was subjected to diastereoselective hydroboration. 

As a consequence of the complimentary electron demand of the nitroalkene and the product nitronate, there exists the possibility of a one-pot, tandem reaction. In this case, the nitroalkene will react preferentially with the electron-rich alkene to produce an intermediate nitronate. This nitronate can then react with a second alkene bearing an electron-withdrawing substituent. Therefore subjection of the nitroalkene 210 to both ethyl vinyl ether and acrylonitrile provides only the nitroso acetal 211 in moderate yield (Eq. 20) (70). Moreover, this also allows the possibility of intramolecular variants of the process. 

There are very few examples of photolysis being used for preparation of a carbonyl ylide. The Dittami protocol follows work completed from his lab with aryl vinyl sulfides. Photolysis, followed by cycloaddition, led to the cycloadduct 305 in excellent yield and stereoselectivity. If the aryl vinyl ether 304 was subjected to irradiation in a mixed solution of toluene-methanol at 366 nm rather than a single solvent of toluene, cyclized product was obtained, but no cycloadduct was formed. If a simple phenyl aryl ether was subjected to the same tandem conditions, the cyclized product was generated, but no cycloadduct was detected. 

In 2002, Grubbs and co-workers reported the first CM reactions of allyl phosphines.In an initial reaction, subjecting allyl diphenylphosphine to catalyst 5 (5 mol%) failed to produce any of the desired cross-product. However, by protecting the phosphine as its borane complex, CM reactions could be achieved in good yield with high E-selectivity (Equation (5)). Notably, catalyst 5 failed to dimerize borane-protected vinyl diphenylphosphine. This result was attributed to substrate trapping of the catalyst as an unreactive Fischer carbene, a situation analogous to that observed in the CM reactions of alkyl vinyl ethers. 

Since stepwise reactions are not subject to the rules of pericyclic reactions, they are often invoked to explain how reactions in which the rules have been subverted take place. However, there is a small group of thermal [2+2] cycloadditions that seem to be disobeying the rules, and yet may well be pericyclic. One is the reaction of ketenes with electron-rich alkenes, illustrated by the reaction of diphenylketene 2.167 with ethyl vinyl ether 2.166 giving the cyclobutanone 2.168. Another is a group of electrophile-... 

The selectivity of the Complex Formation is a very interesting subject, y - Cyclodextrin, (y - CD) has been found to form inclusion complexes with poly (methyl vinyl ether) (PMVE), poly(ethyl vinyl ether) (PEVE), and poly(n- propyl vinyl ether) (PnPVE) of various molecular weights to give stoichiometric compounds in crystalline states. However, a- cyclodextrin (a - CD) and (3 - Cyclodextrin ((3- CD) did not form complexes with poly (alkyl vinyl ether)s of any molecular weight, y -CD did not form complexes with the low molecular weight analogs, such as diethyl ether and trimethylene glycol dimethyl ether. 

The subject of C11 I /vinyl ether copolymers is covered in detail by T. Takarura, in Modern Fluoropolymers (Schiers, J., Ed.), John Wiley Sons, New York, 1997, Chapter 29, pp. 557-564. 

According to the reaction mechanism in Fig. 6, olefins coordinate axially to the dinuclear Pt111 complexes. Whether olefins actually coordinate to Pt111 is the subject of further research. Pt11 is known to coordinate various olefins, whereas PtIV does not coordinate any of them. Therefore, an attempt was made to isolate the olefin -complex of the Ptm dimer in order to prove the proposed mechanisms in Fig. 6. While no olefin -complex was obtained despite our intensive efforts, pent-4-en-l-ol and ethylene glycol vinyl ether... 

The sensitivity of the vinyl ether bond to acid formed the basis of a method for determination of the vinyl ether-linked phosphoglycerides in a mixture of naturally occurring diacyl, alkyacyl, and alkenylacylphosphoglycerides (Murphy et al., 1993). Such mixtures were treated with acid and then subjected to high-performance liquid chromatography. The presence of a lyso(mono-... 

Into the other category fall reactions subject to general acid catalysis, e.g. the hydrolysis of ethoxyethene (ethyl vinyl ether, EVE) [184]... 

A variety of metal catalysts, based on metals such as Mo, W, Ru, Rh, Pd, and Pt, are available to cyclize enyne ketones (Equation 21). Initially, furan intermediates with a metal carbenoid substituent in the 2-position are formed which can be subjected to subsequent reactions furnishing furans with vinyl ether- <1998JOC4564>,... 

Polymerization of vinyl ethers (VE) has been the subject of a considerable amount of theoretical studies. These monomers can be polymerized through radical initiation but the reaction is very slow and leads only to oligomers. Cationic polymerization initiated by a wide variety of Lewis acids is much more efficient and definitely preferred for homopolymer synthesis. Detailed theoretical aspects, and particularly recent developments concerning the controlled/living cationic polymerization of these monomers, have been discussed as well in previous exhaustive review [1,13,98,99] as in the present book (Chapters 4 and 5), and they will no longer be considered here. 

Oxopentanals may be synthesized from allylic alcohols by 3,3 sigmatropic rearrangement of their vinyl ethers, and subs uent oxidation of the terminal double bond. Cinnamyl alcohol (31) was converted to the allyl vinyl ether (32), which was subjected to Qaisen reairangement to give 3-phenyl-4-pentenal (33) in 50% yield. Oxidation of the terminal double bond of (33) gave 3-phenyl-4-oxopentanal... 

Nucleophilic attack on ( -alkene)Fp+ cations may be effected by heteroatom nucleophiles including amines, azide ion, cyanate ion (through N), alcohols, and thiols (Scheme 39). Carbon-based nucleophiles, such as the anions of active methylene compounds (malonic esters, /3-keto esters, cyanoac-etate), enamines, cyanide, cuprates, Grignard reagents, and ( l -allyl)Fe(Cp)(CO)2 complexes react similarly. In addition, several hydride sources, most notably NaBHsCN, deliver hydride ion to Fp(jj -alkene)+ complexes. Subjecting complexes of type (79) to Nal or NaBr in acetone, however, does not give nncleophilic attack, but instead results rehably in the displacement of the alkene from the iron residue. Cyclohexanone enolates or silyl enol ethers also may be added, and the iron alkyl complexes thus produced can give Robinson annulation-type products (Scheme 40). Vinyl ether-cationic Fp complexes as the electrophiles are nseful as vinyl cation equivalents. ... 

The ability of charged substituents to accelerate the 3,3-sigmatropic reiarrangement of allyl vinyl ethers (the Claisen rearrangement) has also been documented. The effect of oxyanion substituents on the rate and course of aliphatic Claisen rearrangements has been the subject of particular attention. " In 1972, Ireland and Mueller reported that the lithium enolate derivatives of allyl esters undergo rapid and effi-... 

The need for a large excess of the vinyl ether was circumvented to some extent through the use of phenyl vinyl sulfides, as in Eq. (20) [50]. Yields of dihydrobenzofuran cycloadducts (XLVI) were generally good using only 2 equivalents of the vinyl sulfide component, although in one case (R = OMe) the cycloadduct was subject to further oxidation under constant current conditions. 

All cationically polymerizable monomers can be potentially used in this process however, the main study has been focused so far on the most reactive oxirane and vinyl ethers [4], Alkoxysilane derivatives - the most common acid-sensitive monomers for the synthesis of siloxane materials through the use of sol-gel methods - were not used extensively. Only a few examples of their application in photo-activated cross-linking can be noted, mainly in co-reaction with oxirane sites [5]. Typically, alkoxysilanes are subjected to an acid- or base-catalyzed process involving hydrolysis of an =SiOR group and then condensation of the formed silanol with another molecule bearing an =SiOH or =SiOR function to give a siloxane linkage [6]. It was of interest to combine the properties of cross-linked silicone materials with the ones provided by sterically overloaded... 

---