Rearrangements of cyclobutenones. Electrocyclic ring closure and thermal ring expansions of 3-allenyl- and 3-alkynyl-2-dienyl-4,4-dimethoxycyclobutenones.
TL;DR: Thermal rearrangements of 2-allenyl- and 2-alkynyl-3-(2-ethenylphenyl)-4,4-dimethoxycyclobutenones were studied and showed to be viable synthetic precursors to benzo[a]anthracene-7,12-diones, compounds representing the framework of the angucycline group of naturally occurring antibiotics.
Abstract: Thermal rearrangements of 2-allenyl- and 2-alkynyl-3-(2-ethenylphenyl)-4,4-dimethoxycyclobutenones were studied. At ambient temperature, the allenyl compounds undergo an electrocyclic cascade to give bicyclo[4.2.0]octadienyl-fused cyclobutenones. These unusual tetracyclic cyclobutenones were shown to be viable synthetic precursors to benzo[a]anthracene-7,12-diones, compounds representing the framework of the angucycline group of naturally occurring antibiotics. In contrast, the 2-alkynylcyclobutenones are stable at ambient temperature but undergo a facile rearrangement at 110 degrees C (toluene) to give the previously unknown naphthalene derivatives, 1,2-dihydro-2,2-dimethoxy-1-(3-alkenylidene)naphtho[2,1-b]furans.
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TL;DR: In this paper, the chemoselective defluoromethoxylation reactions of 2-trifluorsomethyl-1,3-enynes were developed.
9 citations
TL;DR: Vinyl ketenes are usually highly reactive, except when bulky groups and silyl substituents are present as mentioned in this paper, and are extensively utilized in cycloaddition reactions and electrocyclizations, including dimerization, inter- and intramolecular reactions with alkenes, alkynes, imines, and carbonyl groups, and inter-and intra-chemical reactions with aryl and heteroaryl groups.
Abstract: Vinylketenes may be prepared by the typical procedures used for other ketenes, and are usually highly reactive, except when bulky groups and silyl substituents are present. They are extensively utilized in cycloaddition reactions and electrocyclizations, including dimerizations, inter- and intramolecular reactions with alkenes, alkynes, imines, and carbonyl groups, and intramolecular reactions with aryl and heteroaryl groups. These pericyclic reactions are widely used in syntheses of carbocyclic and heterocyclic products, and are particularly useful for the preparation of β-lactams and β-lactones. Allenylketenes and alkynylketenes also undergo cycloaddition and electrocyclic reactions.
Keywords:
Vinylketenes;
allenylketenes;
alkynylketenes;
cycloaddition;
electrocyclization;
diazo ketones;
cyclobutenones;
cyclohexadienones;
acyl chlorides;
β-lactams;
β-lactones
6 citations
TL;DR: A series of fluorene-fused benzoquinones (Q1-Q5) were prepared by thermolysis of 4-fluorenyl-4-hydroxycyclobutenones with potential use of compound Q2 as a reactive oxygen species detector.
Abstract: A series of fluorene-fused benzoquinones (Q1–Q5) were prepared by thermolysis of 4-fluorenyl-4-hydroxycyclobutenones. Red fluorescence observed for Q2 is switched by reduction to blue fluorescence by formation of the hydroquinone. Reaction with hydrogen peroxide restores the original fluorescence colour. The potential use of compound Q2 as a reactive oxygen species detector is discussed.
6 citations
TL;DR: Dichlorocyclobutenone acetals, available via the cycloaddition of dichloroketene and alkynes followed by acetalization, undergo selective SN2' attack by various nucleophiles to give a variety of functionalized cyclobutene derivatives in high yields.
Abstract: Dichlorocyclobutenone acetals, available via the cycloaddition of dichloroketene and alkynes followed by acetalization, undergo selective SN2’ attack by various nucleophiles to give a variety of functionalized cyclobutene derivatives in high yields.
5 citations
01 Jan 2006
TL;DR: A variety of methods for organic transformation starting from squaric acid have been developed in the decade as mentioned in this paper, which are based on conversion of pseudoaromatic 3,4-dihydroxy-3-cyclobutene-1,2-dione derivatives into the more reactive 4-hydroxy-2,cyclobutenone by introduction of the required (or desired) functional groups followed by key ring trans- formation.
Abstract: A variety of methods for organic transformation starting from squaric acid have been developed in this decade. These are based on conversion of pseudoaromatic 3,4-dihydroxy-3-cyclobutene-1,2-dione into the more reactive 4-hydroxy-2-cyclobutenone by introduction of the required (or desired) functional groups followed by key ring trans- formation, the rearrangement being stimulated thermally or induced by a reactive inter- mediate. These strategies can construct a variety of bioactive heterocycles when func- tional groups contain heteroatoms or heterocycles. Interestingly, squaric acid is rendered as an acid part, for example, of an amino acid, and this bioisostere concept is extended to various heterocycle-containing squaramides (3,4-diamino-3-cyclobutene-1,2-dione derivatives) as bioactive conjugate compounds. This review article covers biologically interesting heterocyclic compounds accessible with the squaric acid based technology.
4 citations
References
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Abstract: (11) Potassium ferricyanide has previously been used to convert w'c-1,2-dicarboxylate groups to double bonds. See, for example, L. F. Fieser and M. J. Haddadln, J. Am. Chem. Soc., 86, 2392 (1964). The oxidative dldecarboxylation of 1,2-dlcarboxyllc acids is, of course, a well-known process. See Inter alia (a) C. A. Grob, M. Ohta, and A. Weiss, Helv. Chim. Acta, 41, 1911 (1958); and (b) E. N. Cain, R. Vukov, and S. Masamune, J. Chem. Soc. D, 98 (1969).
4,709 citations
TL;DR: Propargyl ethers HCCCH2OR [R = alkyl or-CH(CH8)(OC2H5)] have been isomerized with good yields into the corresponding allenyl ether's CH2CCHOR by warming with potassium tert-butoxide at 70°.
Abstract: Propargyl ethers HCCCH2OR [R = alkyl or-CH(CH8)(OC2H5)] have been isomerized with good yields into the corresponding allenyl ethers CH2CCHOR by warming with potassium tert.-butoxide at 70°.
These allenyl ethers can be metallated with butyllithium in ether or alkali amides in liquid ammonia. In ether, subsequent alkylation with alkyl halides R′Hal affords α-substituted allenyl ethers CH2CC(R′)OR. Alkylation in liquid ammonia produces a mixture of this same compound and the γ-substituted product R′CHCCHOR. In both cases reasonable yields are obtained. Sodamide and potassium amide quickly convert allenyl ethers CH2CCHOR into metallated propargyl ethers MCC-CH2OR (M = Na or K). If alkylation is not performed almost simultaneously with the metallation with sodamide or potassium amide, the only alkylation product obtained is R′CCCH2OR.
944 citations
TL;DR: In this article, a potentially general regiospecific synthesis of benzo- and naphthoquinones is described, which starts with dimethyl squarate (1), which is converted to the cyclobutenone ketal 9 upon sequential treatment with an organolithium reagent and then BF 3 etherate or TFAA in THF/methanol.
Abstract: A potentially general regiospecific synthesis of benzo- and naphthoquinones is described. This method starts with dimethyl squarate (1), which is converted to the cyclobutenone ketal 9 upon sequential treatment with an organolithium reagent and then BF 3 etherate or TFAA in THF/methanol. Treatment of these with a second lithium reagent followed by hydrolysis gives the cyclobutenones 5.Addition of an alkynyl-,alkenyl- or aryllithium agent to 5 followed by hydrolysis of the ketal linkage gives the corresponding 4-alkynyl-4-alkenyl- or 4-aryl-4-hydroxycyclobutenones 7-9 and these readly rearrange to the respective quinones or hydroquinones upon thermolysis in refluxing benzene.In a similar fashion,15 was employed as a reagent to prepare mono- and disubstituted hydroquinones and quinones
48 citations
6 citations