Reactions, with vinyl ethers

Vinyl ethers undergo many cycloaddition reactions similar to those which take place with enamines. In general, however, these cycloaddition reactions with vinyl ethers take place less readily than those with enamines. These reactions include cycloaddition of vinyl ethers with ketene (200-205), phenyl isocyanate (206), sulfene (207,208), methyl acrylate (209), diethyl acetylenedicarboxylate (210), and diphenylnitrilimine (183). 

Both ( )-l-phenylsulfonyl and (5)-(+)-3-p-tolylsulfmyl -alk-3-en-2-ones can exhibit high diastereoselectivity in their reactions with vinyl ethers and styrenes, with the dienophile having a dominant influence on the stereochemical outcome <96T1205,96TL3687>. Indol-2-ylideneacetic acid esters can act as both dienophile and heterodiene in cycloaddition reactions in the latter case pyrano[3,2-h]indoles are formed <96SYN519>. 

Berberinium chloride (45) also undergoes stereospecific cycloaddition reactions with vinyl ethers or cyclopentadiene. ... 

The high regiospecificity observed in these reactions corresponds to polarization of the methide as shown (281). This is particularly apparent in the reaction with vinyl ethers ethyl vinyl ether affords the 2-ethoxychroman in quantitative yield and dihydropyran gives the pyranopyran (282 Scheme 74) (70JOC3666). 

The structure of the carbenoid has considerable effect on the outcome of the reaction with vinyl ethers. Unlike the case with diazoacetate, reaction with diazopyruvate resulted in the formation of a dihydrofu-ran (17) rather than a cyclopropane (equation 8).26d The reaction is a formal [2 + 3] cycloaddition but it... 

An /V-allylaminium cation radical undergoes an addition-cyclization reaction with vinyl ethers in the presence of t-BuSH to give 3-alkoxy-4-methylpyrrolidines 72 (Scheme 23) in fair to good yields (90TL1675). In addition to EVE, 2,3-dihydrofuran and 3,4-dihydro-(2//)pyran also undergo reactions to give bicycles 73 and 74, respectively, in reasonable yield. 

It has been assumed that the reaction of vinylsilanes with vinyl alkyl sulfides would also occur in the same manner as the reaction with vinyl ether [9] or vinyl pyrrolidinone [17], exhibiting active silylative coupling and inactive cross-metathesis. Nevertheless, we have observed the reverse. 

Diethyl 2-oxo-3-alkenylphosphonates, which are readily accessible from diethyl 2-oxopropylphos-phonate, are useful heterodienes in Diels-Alder reactions. Cycloaddition reactions with vinyl ethers in ( I I in a sealed tube at 85-130°C give satisfactory yields (57-88%) of dihydro-27/-pyrans. The products are isolated as a mixture of 2,4-tra .v and 2,4-czT isomers. When treated with 4 M HCl in THF, the dehydropyran hemiacetal moiety is readily hydrolyzed to provide diethyl 5-formyl-2-oxopentylphosphonates in excellent yields (72-92%, Scheme 5.59). When R> = R =H, the aldehyde undergoes smooth cyclization leading to diethyl 2-oxocyclohexenephosphonate. ... 

Wada, E., Kanemasa, S., and Tsuge, O., New synthesis of 2-oxo-3-alkenylphosphonates and hetero Diels-Alder reactions with vinyl ethers leading to 5-substituted 2-phosphinyl-2-cyclohexen-l-ones, Bull. Chem. Soc. Jpn., 62, 860, 1989. 

Alkylidene exchange 5.8.2.3.11 Reaction with olefins S.8.2.3.6 Reaction with vinyl ethers 5.8.2.3.11... 

Enamine-aldehydes (80) can also serve as the diene equivalent in the hetero-Diels-Alder reaction with vinyl ethers and yields of... 

Chen et cd. reported their screening methodology for investigating highly active, cationic carbene catalysts. The system of Hofmarm ruthenium-catalyzed olefin metathesis (Scheme 4.10) was successfully studied through systematic variation of structural features of the catalyst and ESI-MS/MS by probing metathesis activity by reaction with vinyl ethers (Scheme 4.11) [33]. 

As shown in Figure 4.8, the metathesis activity could be probed by reaction with vinyl ethers (from m/z 649 to m/z 603 in the daughter-ion spectrum). The extent of... 

Similarly, reaction with vinyl ethers generates less active Fischer carbene species. Grubbs and coworkers have prepared and characterized a series of these complexes, via metathesis of the corresponding alkene with G1 or G2 (e.g. Scheme 2.34). While these species can still perform metathesis, they are poorly active, and require high temperatures at which there are competing decomposition reactions to yield hydridocarbonyl complexes. 

Figure 3.2 Reaction with vinyl ethers, (top with substituted vinyl ethers. A functional arrow) Nonfunctional termination (methylene group or fragment R is transferred onto the transfer) of a living ROMP with ethyl vinyl polymer chain end. ether, (bottom arrow) Functional termination...

The [2+2] cycloaddition reaction of isocyanates proceeds better with olefins having electron donating groups attached to the double bond system. Examples include vinyl ethers, enamines, ketene acetals, tetraalkoxy- or tetraalkylaminooleflns. The more reactive sulfonyl and carbonyl isocyanates undergo cycloaddition reactions with vinyl ethers especially well. For example, the reaction of vinyl ethers with p-toluenesulfonyl isocyanate affords the [2+2] cycloadducts in a stereospecific reaction... 

Across carbon multiple bonds The [2-1-2] cycloaddition reaction of isothiocyanates occurs readily with activated olefins, such as enamines and ketene acetals. For example, arene-sulfonyl isothiocyanates undergo a regiospecific [2-1-2] cycloaddition reaction with vinyl ethers at 50 °C to give 2-thietan imines 24. ... 

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