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Homoallylic Ethers (homoallylic + ether)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Metal-Catalyzed Rearrangement of Homoallylic Ethers to Silylmethyl Allylic Silanes in the Presence of a Di-tert-butylsilylene Source.

CHEMINFORM, Issue 14 2006
Pamela A. Cleary
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

Zirconium-Mediated Conversion of Homoallylic Ethers into Cyclopropane Derivatives.

CHEMINFORM, Issue 39 2003
Vincent Gandon
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

ChemInform Abstract: Facial-Selective Allylation of Methyl Ketones for the Asymmetric Synthesis of ,-Substituted Tertiary Homoallylic Ethers.

CHEMINFORM, Issue 12 2002
Lutz F. Tietze
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Asymmetric Allylation of Methyl Ketones by Using Chiral Phenyl Carbinols

CHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2009

Abstract To methyl or to alkyl? High induced facial selectivities and excellent yields are obtained in the allylation of aliphatic methyl ketones by using a structurally simple phenylbenzyl auxiliary to give the corresponding homoallylic ethers (see scheme). The transferred auxiliary has a very good protecting quality and can easily be removed. Novel chiral auxiliaries for the stereoselective allylation of aliphatic methyl ketones with allyltrimethylsilane and their use in the synthesis of homoallylic ethers are described. In a multicomponent domino process catalyzed by trifluoromethanesulfonic acid, the allyl moiety and the auxiliary are transferred onto the substrate to yield tertiary homoallylic ethers. The most useful auxiliary for a general application turned out to be the trimethylsilyl ether of phenyl benzyl carbinol with an induced diastereoselectivity of 90:10 using ethyl methyl ketone and 94:6 using isopropyl methyl ketone as substrates. The transferred substituted benzyl moiety has good protecting properties in subsequent transformations and can easily be removed under reductive conditions to provide the corresponding homoallylic alcohol. The origin of the high selectivity could be elucidated by identifying the relevant transition states using quantum-chemical calculations. An excellent agreement between calculated and experimentally observed selectivities was obtained assuming an oxocarbenium ion as intermediate. [source]

Stereoselective Allylation of Ketones: Explanation for the Unusual Inversion of the Induced Stereochemistry in the Auxiliary-Mediated Crotylation and Pentenylation of Butanone by DFT Calculations

CHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2009

Abstract The solvent makes the difference: While attack at the Re face of the intermediate oxocarbenium ion becomes less energy demanding with increasing size of R,, it is the solvent effect that makes this attack the main trajectory, leading to inversed stereochemistry (see picture). Auxiliary-mediated domino crotylations and pentenylations of butanone yield homoallylic ethers with two newly formed stereogenic centers. With our norpseudoephedrine-derived auxiliary, we observed the formation of anti isomers exclusively, and the nature of the major isomer was independent of the substrate double bond geometry. Interestingly, there is a switch in induced selectivity when going from crotylation to pentenylation. Here, we present the computational rationalization for this behavior by identification of the relevant transition states (TSs), the energies of which were determined by using the B3LYP/6-31+G(d) level of theory in combination with the PCM/UAKS method to include the effects exerted by the solvent dichloromethane. To quickly narrow down the number of potentially relevant TSs from the whole set of 288 and 864 TSs for the crotylation and pentenylation, respectively, we employed a screening process based on B3LYP//AM1 energies. The predicted selectivities are in good agreement with experimentally determined ones. Furthermore, the obtained results also facilitate an explanation of the selectivities obtained in hexenylations and heptenylations. Finally, activation energies were determined that account for the significantly longer reaction times than those for the domino allylation with unsubstituted trimethylallylsilane. [source]