7214-35-9Relevant articles and documents
Concave reagents. 20. Sterically shielded m-terphenyls as selective agents in general protonations
Luening,Baumgartner,Manthey,Meynhardt
, p. 7922 - 7926 (2007/10/03)
New m-terphenyls with acidic substituants in the 2′-position have been used in general protonations leading to reagent-controlled selectivity enhancements: up to 96:4 for the γ/α-protonation of unsymmetrically substituted allyl anions, up to 97:3 for the protonation of cyclohexyl anions generating preferentially the thermodynamically less stable cis-products. In order to allow a general, reagent-controlled protonation the acidity of the protonating agent should be as low as possible.
Cycloalkylmethyl Radicals. Part 3. Dynamic Stereochemistry of Axial and Equatorial Cyclohexylmethyl and 4-Alkylcyclohexylmethyl Radicals
Ingold, Keith U.,Walton, John C.
, p. 1337 - 1344 (2007/10/02)
For cyclohexylmethyl and 4-alkylcyclohexylmethyl radicals the conformer in which the CH2. group adopts the axial position and that in which the CH2. group adopts the equatorial position can both be observed by e.s.r. spectroscopy.At 140 K the axial conformers have a(Hβ) ca. 42-43 G; the equatorial conformers have a(Hβ) ca. 30-31 G.For cis-4-methylcyclohexylmethyl radicals the ratio of the concentrations of the two conformers was studied as a function of temperature and shown to depend on the rate of radical ring inversion vs. the radical lifetime; the rate constant for ring inversion was obtained.As a check on the e.s.r. results the conformational equilibrium of cis-4-methylcyclohexylmethyl bromide was studied by 1H n.m.r. spectroscopy, which gave -ΔG0300(CH2Br) = 1.91 kcal mol-1.The relative conformer concentrations were also measured as a function of temperature for cyclohexylmethyl radicals and the conformational free energy difference of the CH2. group (-ΔG0300) was found to be 0.71 kcal mol-1.The preponderance of the conformer of the cis-4-methylcyclohexylmethyl radical with the CH3 group axial at T . group cannot because of its planarity.The barriers to rotation about the Cα-Cβ bonds in the axial radicals were found to be ca. 1.0 kcal mol-1 greater than those of the equatorial radicals; this is responsible for the greater a(Hβ) values of the axial radicals.The axial and equatorial conformers of cyclohexylmethyl radicals were investigated by semi-empirical SCF MO-methods.
Stereochemistry of Decarbalkoxylation of Cyclic Geminal Diesters Effected by Water and Lithium Chloride in Me2SO
Krapcho, A. Paul,Weimaster, John F.
, p. 4105 - 4111 (2007/10/02)
The stereochemical consequences of the decarbalkoxylation of cyclic geminal diesters by LiCl-H2O-Me2SO have been examined.The norbornene diester 13 and the norbornane diester 16 lead predominantly to the exoesters 14 and 17, respectively.The 2-methylcyclohexane diester 22 leads to esters containing more cis (23) than trans (24) isomer.The diesters 19,25, and 28 lead to nearly equal amounts of the cis and trans esters.In these latter cases,the enolates generated from the esters (via LDA) are protonated in a nonstereoselective fashion on quenching with water.This is suggestive of an enolate intermediate in the decarbalkoxylation reaction.The implications of these sterochemical results are discussed.
