Butenone

Adducts (278) and (279) are derived formally from addition of cw-acetoxy-butenone, whereas the starting material contained ca. 90% of the trans-isomer. Since irradiation of the latter leads to a mixture of 30% cis- and 70 % tra 5-enones, it is possible that (278) and (279) result from the addition to (276) of the more reactive cw-isomer formed by photochemical isomerization prior to cycloaddition. 

The kineties of nueleophilie substitution of the methoxy group in methoxy-butenone by the diethylamino group has been studied (91MIl).Thus, the reae-tions of 4-heterobut-3-en-2-ones with amines presented below often involve the transamination step. 

Under acid-catalyzed conditions (80°C, 10% H2SO4, H2O, 3 h) dialkylamino-butenones afford a mixture of 5-methyl-2,3-dihydro-l,4-diazepine tautomers 4 in 42% yield (84DIS). 

Substitution of the methoxy group in methoxybutenone with mereaptoaeetie aeid ester results in 4-(ethoxyearbonylmethylthio)-4-methoxybutan-2-one (315) whieh further eliminates methanol to give butenone 316. The latter forms 2-ethoxy-earbonyl-3-methylthiophene (318) via dehydration of the intermediate 317 (80MI1). 

Thus, 4-amino- and 4-alkoxybut-3-en-2-ones react with 1,3-dipoles involving only the carbon-carbon double bond, the negative part of the 1,3-dipole adding to position 4 of the butenone. The heterocyclizations are accompanied by elimination of the 4-hetero group. 

Pyrano[3,4-i]indol-3-one (329) enters the Diels-Alder reaetion with methoxy-butenone as an eleetron-rieh olefin [92JCS(P1)415]. After deearboxylation of the primary adduet330,2-aeetyl-3-methoxy-l, 9-dimethyl-2,3-dihydroearbazole (331) eliminates methanol to form 2-aeetyl-l,9-dimethylearbazole (332) [92JCS (Pl)415]. 

Water s internal pressure acts on the volume of activation (AV ) of a reaction in the same way as an externally applied pressure does. Thus, the internal pressure of water influences the rates of nonpolar reactions in water in the same direction as external pressures. Nonpolar reactions with a negative volume of activation will thus be accelerated by the internal pressure of water, whereas nonpolar reactions with a positive volume of activation will be slowed by the internal pressure. For example, at 20° C the rate of Diels-Alder reaction between cyclopentadiene and butenone, which is known to have a negative volume of activation, in a 4.86 M LiCl solution is about twice as that of the reaction in water alone (Eq. 1.1).4... 

The Diels-Alder reaction is one of the most important methods used to form cyclic structures and is one of the earliest examples of carbon-carbon bond formation reactions in aqueous media.21 Diels-Alder reactions in aqueous media were in fact first carried out in the 1930s, when the reaction was discovered,22 but no particular attention was paid to this fact until 1980, when Breslow23 made the dramatic observation that the reaction of cyclopentadiene with butenone in water (Eq. 12.1) was more than 700 times faster than the same reaction in isooctane, whereas the reaction rate in methanol is comparable to that in a hydrocarbon solvent. Such an unusual acceleration of the Diels-Alder reaction by water was attributed to the hydrophobic effect, 24 in which the hydrophobic interactions brought together the two nonpolar groups in the transition state. 

The stereoselectivity of some Diels-Alder reactions was also strongly affected in water.26 At low concentrations, in which both components were completely dissolved, the reaction of cyclopentadiene with butenone gave a 21.4 1 ratio of endo/exo products when they were stirred at 0.15 M concentration in water, compared to only a 3.85 1 ratio in excess cyclopentadiene and an 8.5 1 ratio with ethanol as the solvent. Aqueous detergent solution had no effect on the product ratio. The stereochemical changes were explained by the need to minimize the transition-state surface area in water solution, thus favoring the more compact endo stereochemistry. The results are also consistent with the effect of polar media on the ratio.27... 

S,y-Unsaturated ketones undergo a rearrangement that is formally like the di-77-methane photorearrangement. An example of this rearrangement is provided by the photolysis of l,2,4,4-tetraphenyl-3-butenone ... 

Fig. 9 Generation of DNA-cleaving diradicals from 4-alkynyl-3-methoxy-4-hydroxycyclo-butenones...

DePuy, as early as 1966 [14], reported that cw-1-methyl-2-phenylcyclopropanol gave exclusively deuterated 4-phenyl-2-butenone in 0.1 M NaOD/D20/dioxane. However, homoenolates derived from simple cyclopropanols by base-induced proton abstraction fail to react with electrophiles such as aldehydes and ketones, which would afford directly 1,4-D systems. Lack of a reasonably general preparative method was another factor which impeded the studies of homoenolate chemistry. For this reason, in the past twenty years more elaborated cyclopropanols, which might be suitable precursors of "homoenolates", have been prepared and studied. 

Martin et al. (115) found that miinchnone 38 reacts with isopropyhdenecyclo-butenone (204) to form dihydroazepine 205. At room temperature the two bis(adducts) 206 and 207 were isolated, although the regiochemistry of the cycloaddition has not been established. 

Die Umsetzung von aktivierten Ethenen (z. B. Butenon, Acrylsaure-ester, Acrylnitril) mit N-Methyl-anilin oder 2-Brom-anilin und 1,4-Benzoehinon in Tetrahydrofuran in Gegen-wart von Lithiumchlorid und 0,1 Mol-Aquivalenten Bis-[acetonitril]-palladium-dichlorid fiihrt zur Aminierung der Methylen-Gruppe der Ethen-Derivate2. 

Heteroatoni groups such as boron or silicon can activate or direct synthetic reactions. Use of such activation has become of major importance in organic syntheses. Examples in this volume are BORANES IN FUNCTIONALIZATION OF DIENES TO CYCLIC KETONES BICYCLO[3.3.1]NONAN-9-ONE and BORANES IN FUNCTIONALIZATION OF OLEFINS TO AMINES 3-PINANAMINE. Use of trimethylsilyl or trimethyl-silyloxy groups to activate a 2-butenone or a butadiene are illustrated by the preparations 3-TRIMETHYLSILYL-3-BUTEN-... 

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