3211-27-6Relevant academic research and scientific papers
Hydrogen shifts in cyclohexylcarbenes. Spatial dependence of activating power and of primary deuterium isotope effects
Kenar, James A.,Nickon, Alex
, p. 14871 - 14894 (2007/10/03)
The conformationally biased ketones 4-t-butyl-cis-2-methylcyclohexanone (1c) and 4-t-butyl-cis-2-trans-6-dimethylcyclohexanone (7a; and its 2,6-dideuterio derivative 7c) were converted into p-toluenesulfonylhydrazone Li salts. Thermolysis or photolysis generated putative singlet carbenes, which underwent competitive axial vs equatorial H shift (or D shift in the case of 7c) to give alkenes. Product analysis showed that a bystander Me(eq) substituent promotes a geminal H shift several times more efficiently than does a bystander Me(ax). This geometry-dependent activating power parallels behavior noted earlier for OMe and Ph bystander groups; but as Me groups are rotationally symmetric and possess no lone pair or π electrons this phenomenon cannot be attributed solely to rotameric considerations or to effects involving mobile electron clouds. For the trans-dimethylcarbenes 10a and 10c the primary deuterium isotope effect (k(H)/k(D)) for axial migration (I(ax)) was determined to be ca. 1.5 times larger than that for equatorial migration (I(eq)). This finding invalidates the common assumption that I(ax) = I(eq) and suggests that published data on deuterium isotope effects and on H(ax)/H(eq) migration selectivities need to be adjusted.
Axial/equatorial proportions for 2-substituted cyclohexanones
Basso,Kaiser,Rittner,Lambert
, p. 7865 - 7869 (2007/10/02)
Axial-equatorial conformational proportions have been measured for 2- substituted cyclohexanones in chloroform by the Eliel method for F, Cl, Br, I, MeO, MeS, Me2N, MeSe, and Me. For the first seven of these, at least five experimentally independent measurables were used and the resulting conformational preferences appear to be accurate to within 10%. Systematic errors degraded the results for MeSe and Me. For Me2N, the conformational preference also was measured for the first time at slow exchange in the low- temperature 13C spectrum in several solvents. In chloroform, steric and polar effects contribute to the conformational preferences, with steric effects dominant for large groups such as I and MeS.
Activation of Reducing Agents. Sodium Hydride Containing Complex Reducing Agents. 36. Stereoselective Reduction of Alkylcyclohexanones and Rigid Ketones by MCRA's
Fort, Yves,Feghouli, Abdelhafid,Vanderesse, Regis,Caubere, Paul
, p. 5911 - 5915 (2007/10/02)
The stereoselectivity of reduction of selected ketones by a variety of Complex Reducing Agents (resulting from the Aggregative Activation of NaH and symbolized MCRA's) has been investigated.The stereochemistry of reduction is shown to be dependent on the nature of the metal.Steric hindrance plays an important role and the apparent size of the reagents follows the trend MnCRA's > ZnCRA's, CdCRA's > NiCRA's, CoCRA's.On the other hand NiCRA's and CoCRA's have been found as very strong isomerizing reagents.Insertion of the metal species into the C-O bond with formation of metallacycles appears as one of the possible mechanisms intervening during the reduction of ketones by MCRA's.
Stereochemistry of Nucleophilic Reductions of 2-Methyl-4-t-butylcyclohexanones. Further Support for the Linear Combination of SSC and PSC Stereochemical Models
Fang, Jim-Min,Sun, Shih-Feng,Rei, Min-Hon
, p. 747 - 750 (2007/10/02)
trans-2-Methyl-4-t-butylcyclohexanone reacts with lithium aluminum hydride, lithium trimethoxyaluminium hydride and methyl-lithium with equal stereoselectivity of axial attack (i. e. 95 +/- 1 percent).This is attributed to the equal steric strain control
ABOUT THE MECHANISM OF THE REARRANGEMENT OF β-HYDROXYALKYLSELENIDES TO KETONES
Krief, A.,Laboureur, J. L.,Evrard, G.,Norberg, B.,Guittet, E.
, p. 575 - 576 (2007/10/02)
The regio and stereochemistry of the ring enlargement of Β-hydroxyalkyl methylselenides derived from cyclic ketones is disclosed and sheds some light on the intimate mechanism of the rearrangement.
Structure-odour relationships of some new synthetic sandalwood aroma chemicals. Synthesis and olfactive properties in a series of bicyclodecan-3-ols
Witteveen, Jan G.,Weerdt, Anton J. A. van der
, p. 29 - 34 (2007/10/02)
The relationship between chemical structure and sandalwood fragrance in a series of four isomers of 8-tert-butylbicyclodecan-3-ol (4a-d), the unsaturated analogue 5 and the methyl-substituted derivative 17 has been examined.The sandalwood fragrance
Kinetics of Decarboxylation of the Two Epimers of 5-tert-Butyl-1-methyl-2-oxocyclohexanecarboxylic Acid: Lack of Stereoelectronic Control in β-Keto Acid Decarboxylation
Kayser, Robert H.,Brault, Margaret,Pollack, Ralph M.,Bantia, Shanta,Sadoff, Scott F.
, p. 4497 - 4502 (2007/10/02)
Rates of decarboxylation of the two epimers of 5-tert-butyl-1-methyl-2-oxocyclohexanecarboxylic acid have been measured under both acidic and basic conditions at 25 deg C.The decomposition of isomer 1e (methyl and tert-butyl trans) is more rapid than that
Fluoride-Mediated Reactions of Enol Silyl Ethers. Regiospecific Monoalkylation of Ketones
Kuwajima, Isao,Nakamura, Eiichi,Shimizu, Makoto
, p. 1025 - 1030 (2007/10/02)
Treatment of enol silyl ethers with alkyl halides in the presence of benzyltrimethylammonium fluoride and molecular sieves at room temperature gives the corresponding monoalkylated products with high regiospecificity.In most cases no polyalkylated products formed in the reaction.The alkylation reaction is highly chemospecific: esters, epoxides, and even ketones survive the reaction conditions.The reactions of various cyclohexanone derivatives proceed with the preferential axial attack of the electrophile.
13 C shieldings in syn and anti aldimines and ketimines
Fraser, Robert R.,Banville, Jacques,Akiyama, Fuminori,Chuaqui-Offermanns, Noemi
, p. 705 - 709 (2007/10/02)
The 13 C chemical shifts in a variety of aldimines and in both acyclic and cyclic ketimines have been examined.A comparison of the shieldings at the α carbons in syn versus anti stereoisomers shows a consistent upfield shift of 8-11 ppm in the syn isomer.The greater magnitude found in imines vs. oximes or hydrazones is a clear indication of a steric origin for the differential shieldings.The shifts in the imines of cyclohexanones exhibited stereochemically dependent effects of methyl substitution, very similar to those in analogous oxime and hydrazone derivatives.Chemical shift differences in the syn isomers of the α-phenetylimines of chiral aldimines and ketimines allow a facile measurement of diastereomer ratios for such compounds.
