- Photoinduced Molecular Transformations. Part 155. General Synthesis of Macrocyclic Ketones based on a Ring Expansion involving a Selective β-Scission of Alkoxyl Radicals, its Applications to a New Synthesis of (+/-)-Isocaryophyllene and (+/-)-Caryophyllene, and a Conformational Analy...
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The method used for a general synthesis of macrocyclic ketones based on a ring expansion involving a selective β-scission of alkoxyl radicals devised by Suginome and Yamada was extended and modified.Thus, cycloalkanones were transformed into the corresponding α-(ω-iodoalkyl)-cycloalkanones by alkylation of the corresponding lithium enolates with either 1,3-diiodopropane or 1,4-diiodobutane.Treatment of these α-iodoalkyl cyclic ketones with samarium iodide gave bicyclic tertiary alcohols.The generation of the alkoxyl radicals from the bicyclic alcohols by irradiation of the corresponding hypoiodites generated with mercury(II) oxide - iodine - pyridine in benzene resulted in a selective β-scission of their ring-junction bond to give high yields of macrocyclic ketones carrying an iodine which can be removed with tributyltin hydride.The method was then applied to new syntheses of (+/-)-isocaryophyllene and (+/-)-caryophyllene.Thus, ω-iodopropylation of ethyl 7,7-dimethyl-2-oxobicyclooctane-3-carboxylate, followed by cyclization of the resulting α-(ω-iodoalkyl)cycloalkanone with samarium diiodide, gave cis-transoid-cis-ethyl 1-hydroxy-4,4-dimethyltricyclo2,5>undecane-8-carboxylate (69percent).The ethoxycarbonyl group of this tricyclic alcohol was transformed into a methyl group by the standard method.Irradiation of a solution of the hypoiodite, prepared by the method mentioned above, with Pyrex-filtered light gave the corresponding cis-bicycloundecenone (15percent), its exomethylene isomer (2,5>undecan-1-ol mentioned above were correlated with the three products.
- Suginome, Hiroshi,Kondoh, Takahiko,Gogonea, Camelia,Singh, Vishwakarma,Goto, Hitoshi,Osawa, Eiji
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- Electroorganic Chemistry. 140. Electroreductively Intra- and Intermolecular Couplings of Ketones with Nitriles
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Electroreduction of γ- and δ-cyano ketones in i-PrOH with Sn cathode gave α-hydroxy ketones and their dehydroxylated ketones as the intramolecularly coupled products.Guaiazulene, (-)-valeranone, polyquinanes, dihydrojasmone, methyl dihydrojasmonate, and rosaprostol have been synthesized by utilizing this electroreductive intramolecular coupling of γ- and δ-cyano ketones in one of the key steps.Similarly, electroreduction of a mixture of ketone and nitrile gave the corresponding intermolecularly coupled product.The product obtained by the electroreductive intermolecular coupling of (+)-dihydrocarvone with acetonitrile has been found to be the precursor of an effective chiral ligand for the enantioselective addition of diethylzinc to aldehydes.
- Shono, Tatsuya,Kise, Naoki,Fujimoto, Taku,Tominaga, Naoto,Morita, Hiroshi
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p. 7175 - 7187
(2007/10/02)
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- Stereoselectivity in the Formation and Allylic Rearrangement of 8a-Methyl- and 8a-Ethyl-1,2,3,4,4a,7,8,8a-octahydronaphthalenyl Hydroperoxides
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4a-Methyl- and 4a-ethyl-1,2,3,4,4a,5,6,7-octahydronaphthalene have been subjected to singlet oxygen oxygenation, and the various hydroperoxides which are formed have been characterised.Evidence is presented that the 8aβ-alkyl-1,2,3,4,4a,7,8,8a-octahydronaphthalen-4aα-yl hydroperoxides (I; R=Me or Et) rearrange suprafacially and irreversibly in chloroform at 25 deg C to give only the 4aβ-alkyl-2,3,4,4a,5,6,7,8-octahydronaphthalen-2α-yl hydroperoxides (II).Under the same conditions, the corresponding 8aβ-alkyl-1,2,3,4,4a,7,8,8a-octahydronaphthalen-4aβ-yl hydroperoxides rearrange much more slowly.
- Avila, David V.,Davies, Alwyn G.,Davison, Ian G. E.
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p. 1847 - 1852
(2007/10/02)
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- Lanthanides in Organic Synthesis. 3. A General Procedure for Five- and Six-Membered Ring Annulation
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An improved method for cyclization of 2-(ω-iodoalkyl)cycloalkanones utilizing samarium diiodide (SmI2) has been developed.Both five- and six-membered rings can be constructed in excellent yields for the first time by such a process.The reaction takes place under very mild conditions, allowing toleration of a number of functional groups under the reaction conditions.Stereochemical aspects of the reaction heve been delineated.The reaction has been found to be highly stereoselective when cyclization takes place onto cyclopentanone substrates and when 2-substituted-2-(ω-haloalkyl)cycloalkanone precursors are utilized.
- Molander, Gary A.,Etter, Jeffrey B.
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p. 1778 - 1786
(2007/10/02)
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- Hydroboration. 70. The Polycyclic Hydroboration of Acyclic and Cyclic Trienes with Borane in Tetrahydrofuran and Triethylamine-Borane. Reexamination of the Stereochemistry of Isomeric Perhydro-9b-boraphenalenes.
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The hydroboration of 1,4,8-nonatriene (1), 5-methyl-1,4,8-nonantriene (2), 1,3,7-octatriene (3), and trans,trans,trans-1,5,9-cyclododecatriene (4) with borane in tetrahydrofuran (THF) and triethylamine-borane was studied.The hydroboration of the acyclic trienes with borane in THF at 0 deg C produced monomeric bicyclic boranes in low yields.Moreover, thermodynamically stable organoboranes with fused six-membered rings, such as 9-boradecalin (15) and 10-methyl-9-boradecalin (20), were not formed as the major monomeric cyclic products.However, thermal treatment of the hydroboration product from 1 produced 15 as the only monomeric bicyclic o oganoborane in high yield.The thermodynamically favored major product from 2 was 20 which amounted to 62percent of the monomeric boranes formed in 74percent yield.With 1 and 2, both borane in THF and triethylamine-borane gave comparable results after thermal treatment.However, in the hydroboration of 3, use of triethylamine-borane resulted in a considerably higher yield of perhydro-8-boraindan.The carbonylation-oxidation of 15 provided an 80:20 mixture of cis- and trans-9-decalols.The ratio of cis-10-methyl-9-decalol to its trans isomer obtained by the carbonylation-oxidation of 20 was at least 62:1.The carbonylation-oxidation of 3 produced only cis-8-hydrindanol.The hydroboration of the cyclic triene 4 followed by thermal treatment at 160 deg C for 6 h produced a mixture consisting largely of cis,trans-perhydro-9b-boraphenalene (6) and a constitutional isomer in 83percent yield.However, thermal treatment at 200 deg C for 6 h provided a 92:8 mixture of 6 and its all-cis isomer 5, uncontaminated with the constitutional isomer.The hydroisomerization of 5 or 6 at 220 deg C in the presence of triethylamine under 140 atm of hydrogen gave an equilibrium mixture of 88+/-1percent 5 and 12+/-1percent 6.The difference between thefree energies of 5 and 6 was estimated to be 1.9+/-0.1 kcal/mol.The stereochemistry of 5 and 6 established by 1H NMR examination of the pyridine adducts of 5 and 6 as well as of free 5 and 6.The original structural assignments by Rotermund and Koester must therefore be reversed.
- Brown, Herbert C.,Negishi, Ei-ichi,Dickason, William C.
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p. 520 - 527
(2007/10/02)
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