- Reductive cleavage of acetals and ketals with 9-borabicyclo[3.3.1]nonane
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The reductive cleavage of benzaldehyde acetals and acetophenone ketals with the air-stable crystalline 9-borabicyclo[3.3.1]-nonane dimer provides monobenzylated ether derivatives of diols and 1,2-oxygen-transposed β-phenethyl alcohols, respectively. The boron moiety is effectively recovered through simple procedures which involve convenient air-stable reagents and boron byproducts. The process is particularly selective for 1,3-diols giving the more substituted monobenzyl ether derivatives exclusively. With acetophenone ketals both reduction and elimination occur, permitting 9-BBN-H to hydroborate the resulting styrene to produce 1,2-oxygen-transposed β-phenethyl alcohols cleanly. Potential applications of this new process were illustrated with the synthesis of the hallucinogen, mescaline, and the analgesic, ibufenac.
- Soderquist, John A.,Kock, Iveliz,Estrella, Maria E.
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supporting information
p. 1076 - 1079
(2012/12/23)
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- Diastereoselectivity in the reduction of α-oxy- and α-amino-substituted acyclic ketones by polymethylhydrosiloxane
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Diastereoselectivity in the reduction of α-alkoxy-, α-acyloxy-, and α-alkylamino-substituted ketones with polymethylhydrosiloxane (PMHS) in the presence of fluoride ion catalysis was investigated. High syn-selectivity was observed in the reduction of α-alkoxy, α-acyloxy, and α-dialkylamino ketones. Reduction of α-monoalkylamino ketone proceeded in anti-selective manner with moderate selectivity. The observed selectivity is explained based on Felkin-Anh and Cram-chelate models.
- Nadkarni, Durgesh,Hallissey, James,Mojica, Carlos
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p. 594 - 596
(2007/10/03)
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- Hydrogenation of α-Keto Ethers: Dynamic Kinetic Resolution with a Heterogeneous Modified Catalyst and a Heterogeneous Base
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The first successful example of the asymmetric hydrogenation of substituted α-keto ethers with Cinchona-modified Pt/Al2O3 is reported. In the absence of an additional base, kinetic resolution of the racemic starting material was observed with high diastereoselectivity and ee's up to 98% at conversions of a strong reaction acceleration but racemic product. Immobilization of OH- on solid ion exchangers resulted in the desired dynamic kinetic resolution, and ee's of >80% were obtained at >95% conversion. These effects are rationalized on the basis of a simple kinetic and structural model.
- Studer, Martin,Blaser, Hans-Ulrich,Burkhardt, Stephan
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p. 511 - 515
(2007/10/03)
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- Chelation-controlled reduction of α- and β-oxygenated ketones with lithium tri-n-butylborohydride
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Lithium tri-n-butyl borohydride showed high selectivity in the reduction of α- and β-oxygenated ketones, giving a preponderance of the chelation controlled products.
- Faucher, Anne-Marie,Brochu, Christian,Landry, Serge R.,Duchesne, Isabelle,Hantos, Susanne,Roy, Amelie,Myles, Andrew,Legault, Claude
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p. 8425 - 8428
(2007/10/03)
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- Methylaluminum bis(4-substituted-2,6-di-tert-butylphenoxide) as an efficient nonchelating Lewis acid: Application to asymmetric Diels-Alder reaction and diastereoselective alkylation to alkoxy carbonyl substrates
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The exceptionally bulky methylaluminum bis(4-substituted-2,6-di-tert-butylphenoxide) such as MAD or MABR can be successfully utilized as a highly efficient nonchelating Lewis acid for achieving high stereoselectivity in 1,n asymmetric induction in cyclic
- Maruoka, Keiji,Oishi, Masataka,Shiohara, Kei,Yamamoto, Hisashi
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p. 8983 - 8996
(2007/10/02)
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- Diastereoselective addition of organomanganese compounds to α-alkoxysubstituted propanals
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Reactions of organomanganese compounds R1MnI (R1 = Ph, 4-MeC6H4, Me, Bu, n-C7H15, BuCC, PhCC),prepared from R1Li and MnI2 in Et2O, with aldehydes MeCH(OR2)CHO (R2 = CH2Ph, CH2OMe, CH2OCH2Ph) afford threo-alcohols MeCH(OR2)CH(OH)R1 with high diastereoselec
- Kasatkin, A. N.,Biktimirov, R. Kh.,Podlipchuk, I. P.,Sultanmuratova, V. R.,Tolstikov, G. A.
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p. 161 - 165
(2007/10/02)
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- First direct NMR spectroscopic observation of a Cram-chelate involving a chiral α-alkoxy aldehyde
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The reaction of CH3TiCl3 with 2-benzyloxy propanal 10 at low temperatures in CD2Cl2 leads to the formation of two diastereomeric Cram-type chelates 13a/13b which can be observed directly by 13C-NMR spectroscopy. The octahedral chelates undergo C---C bond formation with first order kinetics, suggesting intramolecular 1,3 methyl transfer. Crossover experiments are unsuitable for definitive proof of intramolecularity due to ligand exchange reactions prior to Grignard-type addition.
- Reetz, Manfred T.,Raguse, Burkhard,Seitz, Thomas
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p. 8561 - 8568
(2007/10/02)
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- SELECTIVE MONOETHERIFICATION AND MONOESTERIFICATION OF DIOLS AND DIACIDS UNDER PHASE-TRANSFER CONDITIONS
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Research on the selectivity of etherification reactions of diols and esterification reactions of diacids by alkyl halides under phase-transfer catalysis has shown that under such conditions, selectivity of monoetherification increases in the order prim sec tert diols, though overall yield of monoether decreases from sec to tert diols.Monoesterification of diacids was accomplished with a high degree of selectivity.Optimal extraction of diols and diacids was found to correspond in general to chain lengths of around 5 carbons.This could mean that the complex formed between the catalyst and the anion to react is stabilized for certain carbon lengths by inner solvation in virtue of its spatial conformation.
- Zerda, Jaime de la,Barak, Gabriela,Sasson, Yoel
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p. 1533 - 1536
(2007/10/02)
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- ZnBr2-MEDIATED HIGHLY DIASTEREOSELECTIVE ADDITION OF GRIGNARD REAGENTS TO α-BENZYLOXY ALDEHYDES
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α-Benzyloxy aldehydes reacted with Grignard reagents in the presence of ZnBr2 to afford vicinal syn-diol derivatives with high diastereoselectivity.
- Asami, Masatoshi,Kimura, Rieko
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p. 1221 - 1222
(2007/10/02)
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- Veretherungen von Diolen, Triolen und Hydroxycarbonsaeurederivaten ueber Thallium(I)-alkoholate. Eine neue Variante der Williamson-Reaktion
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The etherifications listed in tables 1 and 2 are achieved by converting hydroxy-derivatives, which contain additional oxygen functions, into thallium(I) alkoxides with thallium ethoxide, and treatment with haloalkanes.The scope and limitations of the method are discussed.
- Kalinowski, Hans-Otto,Crass, Gerhard,Seebach, Dieter
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p. 477 - 487
(2007/10/02)
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