10035-97-9Relevant articles and documents
Application of Rh(l)-Catalyzed C - H Bond Activation to the Ring Opening of 2-Cycloalkenones in the Presence of Amines
Jun, Chul-Ho,Moon, Choong Woon,Lim, Sung-Gon,Lee, Hyuk
, p. 1595 - 1597 (2002)
(matrix presented) Herein described is the application of the Rh(l)-catalyzed C-H bond activation to the ring-opening of 2-cycloalkenones in the presence of cyclohexylamine. This reaction includes the C-C double bond cleavage of 2-cycloalkenones through the conjugate addition of cyclohexylamine followed by the retro-Mannich-type fragmentation. The resulting ring-opened intermediates subsequently underwent either chelation-assisted hydroacylation to afford a ring-opened dicarbonyl compound or β-alkylation via a ring contraction.
Is pseudorotation the operational pathway for bond shifting within [8]annulenes? Probe of planarization requirements by 1,3-annulation of the cyclooctatetraene ring. Kinetic analysis of racemization and 2-D NMR quantitation of π-Bond alternation and ring inversion as a function of polymethylene chain length
Paquette,Wang,Luo,Cottrell,Clough,Anderson
, p. 239 - 253 (1990)
The chiral 1,3-bridged cyclooctatetraenes 9a-c have been prepared in nine steps from the appropriate 2-cycloalkenone precursors. Following annulation with ethyl acetoacetate to give 15, trans-1,2-dichloroethylene was cycloadded photochemically in a [2 + 2] reaction and a cyclobutene ring was ultimately formed. Once reduction to alcohol 19 was accomplished, dehydration was effected and the bicyclo[4.2.0]octatrienes so generated underwent disrotatory ring opening to deliver the [8]annulenes. The rates of this electrocyclic ring opening were determined in two examples. Polarimetric studies provided quantitative measure of the readiness with which planar dianion formation occurs as a function of loop size. Unexpectedly, attempts to resolve these molecules failed to deliver them in optically active condition because of too rapid enantiomerization via ring inversion and/or bond shifting. The rates of these processes were determined by 2-D dynamic NMR methods, the data revealing that both processes are accelerated relative to nonbridged models. These and related findings are interpreted in terms of a pseudorotation scheme leading to flattened saddle and not planar-alternate transition states. The unique features associated with this mechanistic phenomenon are discussed.
Iodine(V) reagents in organic synthesis. Part 4. o-Iodoxybenzoic acid as a chemospecific tool for single electron transfer-based oxidation processes
Nicolaou,Montagnon,Baran,Zhong
, p. 2245 - 2258 (2007/10/03)
o-Iodoxybenzoic acid (IBX), a readily available hypervalent iodine(V) reagent, was found to be highly effective in carrying out oxidations adjacent to carbonyl functionalities (to form α, β-unsaturated carbonyl compounds) and at benzylic and related carbon centers (to form conjugated aromatic carbonyl systems). Mechanistic investigations led to the conclusion that these new reactions are initiated by single electron transfer (SET) from the substrate to IBX to form a radical cation which reacts further to give the final products. Fine-tuning of the reaction conditions allowed remarkably selective transformations within multifunctional substrates, elevating the status of this reagent to that of a highly useful and chemoselective oxidant.
Recoverable chiral sulfoxides for asymmetric synthesis: application to stereoselective carbonyl reduction and the asymmetric synthesis of allylic alcohols
Butlin, Roger J.,Linney, Ian D.,Mahon, Mary F.,Tye, Heather,Wills, Martin
, p. 95 - 106 (2007/10/03)
The enantiomerically pure cyclic sulfinamide S(S)R-(+)-3 reacts with the sodium enolates of ketones to give the corresponding homochiral sulfoxides.Reduction of the carbonyl group in these products may be achieved using a variety of reducing agents the best of which were DIBAL-H or DIBAL-H/ZnBr2, which give complementary products of high diastereomeric excess.Reduction of the hydroxy sulfoxides with Raney nickel proceeds in low yield and causes partial racemisation of the products.However the combined use of a durected reduction followed by a facile sulfenic acid elimination provides a synthesis of allylic alcohols in high enentiomeric excess.
Sensitized Photooxygenation of Silyl Enol Ethers of Cyclic Ketones
Friedrich, Edgar,Lutz, Werner
, p. 1245 - 1263 (2007/10/02)
α,β-Unsaturated and α-hydroxy ketones are accessible in prototropic ene-reactions with singlet oxygen by sensitized photooxygenation of cyclic silyl enol ethers and subsequent reduction and solvolysis.In a competing silatropic ene-reaction α-silyloxyketones are formed.Formation of different products depends on ring size, configuration and substitution.At C-6 chirally substituted 2-cyclohexenones are synthesized for the first time by sensitized photooxygenation of chiral silyl enol ethers of optically active starting ketones.
The syntheses and conformational studies of [n](2,4)heterophanes and [7](3,5)pyrazolophane
Hirano,Hiyama,Fujita,Kawaguti,Hayashi,Nozaki
, p. 2633 - 2640 (2007/10/09)
Synthetic sequences from (n + 3)-membered 2-cycloalkenones provide furan, thiophene and pyrrole derivatives bridged at the 2,4-positions by n-methylene chains (n = 6, 7, and 9) as well as a pyrazole derivative bridged at the 3,5-positions (n = 7). The molecular geometry as a function of the chain length has been investigated spectrometrically. The aliphatic chain of [7](2,4)pyrrolophane and [7](3,5)pyrazolophane is found to reside in the one side of the respective heteroaromatic rings even at 205°, whereas that of [7](2,4)thiophenophane flips up and down the thiophene ring upon heating, the energy barrier ΔGc≠ being 18·2 kcal/mol (Tc 111°C at 60 MHz). The conformational behaviour of the heptamethylene chain is thus dependent on the angle between the bonds connecting each heteroaromatic carbon with the benzylic one. Though the hexamethylene chain of the [6](2,4)heterophanes is fixed to the one side of the aromatic ring, the nonamethylene chain of the [9]-homologues is rapidly moving between the both sides even at room temperature. The red-shifts of the B-bands are attributed to the distorted, nonplanar heteroaromatic rings. The mass spectra of these heterophanes indicate the initial C(1)-C(2) fission of the polymethylene chain probably due to the steric strain of the systems.
