5- Methoxycarbonyl-2-pyrone

Methoxycarbonyl)- and 5-(methoxycarbonyl)-2-pyrone 309 and 269b provide the cycloheptatrienone ketals 381a-b directly (25°C, 6.2 kbar). The intermediate [4 -I- 2]-cycloadducts 381 a-b or the norcaradienes 381"a-b cannot be detected or isolated. The results observed are consistent with the potential for the strained olefin of the cyclopropenone ketal to exhibit accelerated participation in both inverse-electron-demand (diene LUMO-controlled) and normal (diene HOMO-controlled) Diels-Alder reactions (86T2777). 

Write out a mechanism for the conversion of 4-pyrone into l-phenyl-4-pyridone by reaction with aniline. Write structures for the products you would expect from reaction of methyl coumalate (5-methoxycarbonyl-2-pyrone) with benzylamine. 

Various other nonconjugated dienes have been used as the dieno-phile component in tandem Diels-Alder processes. In these cases, the first cycloaddition occurs as usual. Then cycloreversion with loss of COj is followed by intramolecular Diels-Alder reaction with the remaining pendant alkene to yield bicyclo[2.2.2]octene structures. For example, methyl coumalate (5-methoxycarbonyl-2-pyrone 26) reacts with 1,5-cyclooctadiene under thermal conditions to give the cage compound 27. ... 

Methoxycarbonyl-2-pyrone. It has been reported that the [4+2] cycloaddition reactions of 5-methoxycarbonyl-2-pyrone 41... 

Barrelene was obtained via a double Diels-Alder reaction from a-pyrone with methyl acrylate (H.E. Zimmerman, I969A). The primarily forming bicyclic lactone decarboxylates in the heat, and the resulting cyclohexadiene rapidly undergoes another Diels-Alder cyclization. Standard reactions have then been used to eliminate the methoxycarbonyl groups and to introduce C—C double bonds. Irradiation of barrelene produces semibullvalene and cyclooctatetraene (H.E. Zimmerman. 1969B). 

Diese Reaktionsart ist bei den Addukten aus Butadien-carbonsaure-Derivaten mit der Carboxylgmppe in 3-Stellung allein verwirklicht dabei entstehen 3-Amino-a-pyrone [58, 70, 72). So geht das N-p-Chlorphenyl-3-methoxycarbonyl-6-phenyl-3.6-dihydro-1.2-oxazin bei der Chromato-graphie an Aluminiumoxid in 3-p-Chloranilino-6-phenyl-a-pyron uber (55), der Mechanismus ist analog dem der Pyrrolbildung. 

Methyl-l-penten-3-one-l-ol 1 and glacial acetic acid in benzene was added to pyrrolidine to give 2-methyl-l-pen ten-1-[N-pyrrolidinyl]-3-one 2. Compound 2 when treated with oxalyl chloride and methanol was added, 3,5-dimethyl-2-methoxycarbonyl-4-pyrone 3 was produced. Treatment of compound 3 with sodium borohydride in methanol gives 3,5-dimethyl-2-hydroxymethyl-4-pyrone 4. Compound 4 was converted to 3,5-dimethyl-2-hydroxymethyl-4-pyridone 5 by heating compound 4 with aqueous ammonia in a sealed flask. Compound 5 was converted to 4-chloro-2-chloromethyl-3,5-dimethyl pyridine 6 by treatment with phosphorous oxychloride. Treatment of compound 6 with 5-methoxy-2-mer-captobenzimidazole in tetrahydrofuran gave 2-[2-(4-chloro-3,5-dimethyl pyridinyl)methylthio]-5-methoxy benzimidazole 7. When compound 7 was treated with potassium hydroxide in dimethyl sulfoxide containing methanol, 2-[2-(3,5-dimethyl-4-methoxypyridinyl)methylthio]-5-methoxy... 

Cyclopenten 2,5-Dihydroxy-5-methoxycarbonyl-1 -(4-nitro-anilino)-3-oxo- E15/2, 1252 (5-OH-2-COO R-4H-pyron + R —NH2)... 

H 2]-Cycloaddition occurs between 3-methoxycarbonyl-2-pyrone 309 and a trimethylenemethane Pd[(/-PrO)3P]4 complex to give the cycloadduct 310 in 71% yield (88JA1602). (See Scheme 59.) Reactions of 309 and 3-acetylcoumarin 236a with cyclopropenone acetal derivative 312 afford regioselectivity the cyclopentenone acetal compound 313 and 314, respectively (92JA5523). 

A conceptually different [4-1-2] cycloaddition catalyzed by a chiral lanthanide complex has been disclosed. The inverse electron demand Diels Alder reaction of 3-methoxycarbonyl-2-pyrone (67) and enol ethers or sulfides [135] was catalyzed by a chiral ytterbium(III) triflate-binaphthol complex in the presence of diisopropylethylamine (Scheme 51) [136]. Thermal decarboxylations of bicyclic lactones such as 68 are known to yield dienes which may undergo subsequent pericyclic reactions [137] thus, the adducts of this process are potentially useful chiral building blocks. The nature of the substituent on the 2k component was found to be crucial for the realization of high enantioselectivity. 

Under appropriate conditions, even unactivated alkenes will take part in intermolecular cycloadditions with 3- and 5-bromo-2-pyrones and with 3-methoxycarbonyl-2-pyrone. Reactions can be conducted at 100 °C, or at room temperature under 10-12 kbar and with zinc chloride catalysis. 

In earlier work the o-pyrone shown upon treatment with magnesium methoxide afforded the C-methoxycarbonyl derivative of phloroacetophenone (ref.1). 

As might be expected on the basis of the C NMR chemical shift data, 3-methoxycarbonyl-2-pyrone 33 is less reactive toward vinyl ethers than 3-chlorocarbonyl-2-pyrone. In fact, at room temperature in methylene chloride, no cycloadduct formation was observed with a number of different vinyl ethers. Marko and co-workers, however, coaxed these pyrone dienes into reacting with representative vinyl ethers at elevated temperatures (70°-80 C) in polar aprotic solvents, leading to bicyclic lactones 34-37. In all cases, each of these bicycloadducts is obtained as a single stereoisomer. 

Although electron-rich vinyl ethers can be coerced into reacting with 3-methoxycarbonyl-2-pyrone under either high pressure or Lewis acid catalysis, the same is not true of unactivated dienophiles. Thus... 

Markd and co-workers reported low levels of stereocontrol in the cycloaddition of 3-methoxycarbonyl-2-pyrone and butyl vinyl ether when TADDOL ligands are used in conjunction with YbfOTOj. ... 

Markd and co-workers also explored the use of binol complexes as Lewis acid catalysts for [4-t-2] cycloadditions of 3-methoxycarbonyl-2-pyrone. Marko reported modest to excellent levels of stereocontrol in the cycloadditions of a variety of vinyl ethers with this pyrone (Table 1 i)."b-d,6i gjjjj better results are reported when vinyl thioethers function as the dienophile. It is important to note that these impressive stereochemical results are obtained with catalytic amounts (0.1-0.2 equivalents) of Lewis acid. 

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