15822-50-1Relevant academic research and scientific papers
Axial and Equatorial Hydrogen Shifts in Methyl Substituted Cyclohexylidenes. Stereochemically-dependent Isotope Effects and Bystander Assistance
Kenar, James A.,Nickon, Alex
, p. 9657 - 9660 (1994)
Carbenes were generated from 4-t-butyl-cis-2-methylcyclohexanone (4a) and from 4-t-butyl-cis-2-trans-6-dimethylcyclohexanone (8a, and its corresponding 2,6-d2 analog 8b) by conventional Bamford-Stevens reactions.Product analysis revealed that an equatorial CH3 assists migration of a geminal H more efficiently than does an axial CH3 by a factor of about 4.6.The primary deuterium isotope effect (kH/kD) for axial shift (Iax) is ca. 1.5 times greater than for equatorial shift (Ieq) in the anchored dimethyl substituted carbene 9.
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.
Regioselective dehydration in cyclic system with triphenylphosphine-azodicarboxylate
Iimori,Ohtsuka,Oishi
, p. 1209 - 1212 (2007/10/02)
The regioselective dehydration of cyclohexanol derivatives was achieved by using the Mitsunobu reagent system. The reaction undergoes under mild and neutral conditions. The observed regioselectivity was explained by considering the importance of the orientation of the leaving group at the elimination stage.
Stereoelectronic Effects in Hydrogen-atom Transfer Reactions of Substituted Cyclohexyl Radicals
Beckwith, Athelstan L. J.,Easton, Christopher J.
, p. 661 - 668 (2007/10/02)
Thermolysis of the peroxyoxalates (1)-(7) and the diacyl peroxides (8)-(11) in cyclohexane at 100 deg C gives cycloalkenes and cycloalkanes by hydrogen-atom transfer reactions of the initially formed conformationally biased 4-t-butyl-, 4-t-butyl-cis,cis-2,6-dimethyl-, 4-t-butyl-cis,trans-2,6-dimethyl-, 4-t-butyl-cis-2-methyl-, 4-t-butyl-trans-2-methyl-, and 5-t-butyl-cis-2-methylcyclohexyl radicals (12)-(17).The composition of the product mixtures indicates that transfer of axial β-hydrogen atoms occurs more rapidly than does transfer of equatorial β-hydrogen atoms.These results support the hypothesis that homolytic fission of a C-H bond is favoured when it lies chlose to the plane of an adjacent semi-occupied orbital.
