7500-91-6Relevant academic research and scientific papers
Organic dye-catalyzed radical ring expansion reaction
Deguchi, Masato,Fujiya, Akitoshi,Yamaguchi, Eiji,Tada, Norihiro,Uno, Bunji,Itoh, Akichika
, p. 15825 - 15830 (2018/05/04)
Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation. This synthetic approach featured mild conditions, a facile procedure, a broad substrate scope, and modera
Reactivity of Lithium β-Ketocarboxylates: The Role of Lithium Salts
Berton, Mateo,Mello, Rossella,Williard, Paul G.,González-Nú?ez, María Elena
supporting information, p. 17414 - 17420 (2017/12/15)
Lithium β-ketocarboxylates 1(COOLi), prepared by the reaction of lithium enolates 2(Li+) with carbon dioxide, readily undergo decarboxylative disproportionation in THF solution unless in the presence of lithium salts, in which case they are indefinitely stable at room temperature in inert atmosphere. The availability of stable THF solutions of lithium β-ketocarboxylates 1(COOLi) in the absence of carbon dioxide allowed reactions to take place with nitrogen bases and alkyl halides 3 to give α-alkyl ketones 1(R) after acidic hydrolysis. The sequence thus represents the use of carbon dioxide as a removable directing group for the selective monoalkylation of lithium enolates 2(Li+). The roles of lithium salts in preventing the disproportionation of lithium β-ketocarboxylates 1(COOLi) and in determining the course of the reaction with bases and alkyl halides 3 are discussed.
Cyclizations of unsaturated CR(COX)2 radicals. Manganese(III) acetate oxidative cyclizations of unsaturated acetoacetates and atom-transfer cyclizations of unsaturated haloacetoacetates give the same radicals
Curran, Dennis P.,Morgan, Tina M.,Eric Schwartz,Snider, Barry B.,Dombroski, Mark A.
, p. 6607 - 6617 (2007/10/02)
Comparable regio- and stereochemical results were obtained when cyclizations of a series of 2-substituted 3-oxohept-6-enoate (or oct-7-enoate) esters (acetoacetates) were conducted by manganese(III) acetate oxidation or by iodine or bromine atom transfer
Ultrasound-Promoted Cycloadditions in the Synthesis of Salvia miltiorrhiza Abietanoid o-Quinones
Lee, Junning,Snyder, John K.
, p. 4995 - 5008 (2007/10/02)
The ultrasound-promoted Diels-Alder reaction of 3-methyl-4,5-benzofurandione with appropriately substituted vinylcyclohexenes has led to the synthesis of tanshinone IIA, nortanshinone, tanshindiol B, methyl tanshinonate, and tanshinone IIB, biologically active metabolites of the Chinese traditional medicine, Dan Shen, prepared from the roots of Salvia miltiorrhiza Bunge.Methyltanshinquinone, the dihydro derivative of the natural product, methylenetanshinquinone, was similarly prepared.The effect of ultrasound in promoting the cycloadditions parallels that of high pressure and improved the regioselectivity in favour of the natural isomers.
Asymmetric Alkylation of β-Keto Esters with Optically Active Sulfonium Salts
Umemura, Kazuyuki,Matsuyama,Haruo,Watanabe, Nobuko,Kobayashi, Michio,Kamigata, Nobumasa
, p. 2374 - 2383 (2007/10/02)
Alkylation of the cyclic β-keto ester2-(methoxycarbonyl)-1-indanone (2) with racemic alkylsulfonium salts 1a-h gave 2-alkylindanones 3 and 4 in 60-96percent yields.The relative reactivities of the alkyl substituents of aryldialkylsulfonium salts 1e and 1f were quite different from those in SN2 alkylations.Asymmetric induction occured upon alkylation of 2 with optically active sulfonium salts. (R)-2-Ethyl-2-(methoxycarbonyl)cyclohexanone (11) was obtained in up to 16percent ee by alkylation of the enolate ion of 2-(methoxycarbonyl)cyclohexanone (9) with optically active (R)-(+)-(p-chlorophenyl)ethylmethylsulfonium d-10-camphorsulfonate (1k).Alkylation of the enolate ion of 2 with sulfonium salts containing optically active alkyl groups afforded C-alkylated products with inversion of configuration at the asymmetric alkyl carbon atom.These alkylations appear to proceed via an S-O sulfurane intermediate or a tight ion pair with subsequent stereoselective alkyl migration to the enolate.
Some 6,6-disubstituted 2,4-cyclohexadien-1-ones and the facial selectivity in their Diels-Alder reactions with dimethyl acetylenedicarboxylate
Yates, Peter,Gomes, Anabela,Burnell, Jean D.,Cong, Dong Dao,Sawyer, Jeffery F.
, p. 37 - 47 (2007/10/02)
6,6-Disubstituted 2,4-cyclohexadien-1-ones can be prepared by dibromination-bisdehydrobromination of the corresponding 6,6-disubstituted 2,2-dibromocyclohexanones.Such dienes undergo Diels-Alder reactions with dimethyl acetylenedicarboxylate to give 3,3-disubstituted 5,6-di(methoxycarbonyl)bicycloocta-5,7-dien-2-ones; when the substituents at C-6 in the dienones are different, two diastereomers of the adducts are formed in a ratio dependent on the "facial selectivity" in the Diels-Alder reactions.For the cases where one of the 6-substituents is methyl and the other is methoxycarbonyl, acetoxymethyl, dibromomethyl, or dichloromethyl it has been established via X-ray crystallograpfy and chemical correlation that the endo-3-methyl/exo-3-methyl product ratio is 3.0, 0.9, 8, and 6, respectively.The origin of these differences is discussed briefly and a spectroscopic method for the assignment of structures to the individual diastereomers is proposed.Key words: Diels-Alder reactions, substituted 2,4-cyclohexadien-1-ones, facial selectivity, dimethyl acetylenedicarboxylate.
UNSYMMETRICAL CONNECTIVE OLEFINATION BY KORNBLUM NITRO-SYNTHESIS : APPLICATIONS IN PHYTUBERIN CHEMISTRY
Crombie, Leslie,Roughley, Brian S.
, p. 3147 - 3156 (2007/10/02)
Kornblum unsymmetrical olefin synthesis employing radical-anion chain crossed-coupling (light catalysed) of a mono- and a gem-di-nitro-compound, followed by reductive NO2 removal, is examined in the context of a hindered olefin structure required for phytuberin synthesis.Whilst successful for a tetrasubstituted olefin model (for which a Witting approach failed), increasing substitution on the β-position of the mono-nitro component supressed the coupling reaction, presumably for steric reasons.An alternative coupling involving a bromonitrocyclohexane and a mononitroacetal caused symmetrical coupling of the mononitro-component in high yield, rather than a crossed reaction.Reductive elimination (using Na2S/DMF) from either rac.- or meso- 1,2-dinitro-1,2-diphenylethane leads to (E)-stilbene 98percent (E) > probably through a stabilised radical or anion.A convenient preparation of triphenylisoxazoline-N-oxide is reported.
NOVEL ASYMMETRIC ALKYLATION OF CYCLIC β-KETO ESTERS WITH OPTICALLY ACTIVE SULFONIUM SALTS
Kobayashi, Michio,Umemura, Kazuyuki,Watanabe, Nobuko,Matsuyama, Haruo
, p. 1067 - 1070 (2007/10/02)
A new asymmetric alkylation of cyclic β-keto esters with optically active sulfonium salts, which are easily prepared by optical resolution methods, has been investigated.Relative reactivities for alkyl substituents are found to be quite different from tho
A Short Synthesis of the 4-Demethoxy-11-deoxyanthracycline Skeleton. Regiospecific Enolate C-Carboxylation with Carbon Oxysulfide
Vedejs, E.,Nader B.
, p. 3193 - 3195 (2007/10/02)
Regiospecific C-carboxylation of enolate 2 and COS followed by methylation (CH3I) and cuprous triflate cyclization results in a tetracyclic product 9 which can be converted into 11-deoxyanthracyclines.
Organoiron Complexes in Organic Synthesis. Part 7. Regio- and Stereo-chemistry of Ring Connection Reactions relevant to Steroid and Terpene Synthesis. X-Ray Crystal Structure Determination of Tricarbonyl(methyl 1-<2 - 5-η-4-methoxy-1-methylcyclohexa-2,4-d
Pearson, Anthony J.,Mincione, Enrico,Chandler, Malcolm,Raithby, Paul R.
, p. 2774 - 2780 (2007/10/02)
Reaction of tricarbonyl(1 - 5-η-4-methoxy-1-methylcyclohexadienylium)iron hexafluorophosphate (1) with enolate anions of derivatives of methyl 2-oxocyclohexanecarboxylate and methyl 1-oxotetralin-2-carboxylate occurs with very high regioselectivity for th
