65080-77-5Relevant academic research and scientific papers
The Roles of 2- and 3-Axial Methoxy Groups in Determining the Stereochemistry of the Complex Metal Hydride Reduction of Cyclohexanones: Examination of the Cieplak Model
Senda, Yasuhisa,Sakurai, Hiroshi,Nakano, Shigeru,Itoh, Hiroki
, p. 3297 - 3303 (2007/10/03)
The 2- and 3-axially substituted methoxy groups in cyclohexanones exhibit steric hindrance similar to that of the methyl group in LiAlH4 and NaBH4 reductions. The chelate complex formation between the zinc ion and the two oxygens in the molecule was suggested in the zinc borohydride reduction. The relative reactivities of cyclohexanones in which the 2-axial position is substituted by the methyl or the methoxy group in the LiAlH4 reduction strongly support Cieplak's proposal, which focuses on the importance of the stabilization of the transition state by anti-periplanar allylic bonds.
Mechanism of acid-catalyzed photoaddition of methanol to 3-alkyl-2-cyclohexenones
Schuster, David I.,Yang, Jie-Min,Woning, Jan,Rhodes, Timothy A.,Jensen, Anton W.
, p. 2004 - 2010 (2007/10/03)
Contrary to a previous report, it is concluded that formation of methanol adducts to 3-methyl-2-cyclohexenones and of deconjugated enones on irradiation of the enones in acidified solutions proceeds via protonation of the intermediate enone ?,?* triplet excited state and not by protonation of a relatively long-lived ground state trans-cyclohexenone.A rate constant for protonation of the triplet state of 3-methyl-2-cyclohexenone by sulfuric acid of 1.7*109 M-1 s-1 was determined by laser flash photolysis in ethyl acetate.Based on quantum efficiencies of product formation, a rate constant of ca. 108 M-1 s-1 was estimated for protonation of the enone triplet by acetic acid, which is too small to cause measurable reduction in the triplet state lifetime in the mM concentration range used in the preparative studies.The intermediate carbocation can be trapped by methanol, or revert to starting enone or the exocyclic deconjugated enone by loss of a proton.Since products revert to starting materials in an acid-catalyzed process, there is an acid concentration at which the yields of products are optimal.This concentration is ca. 6mM for acetic acid, but it is only 0.1 mM for p-toluenesulfonic or sulfuric acids.Product formation could be quenched using 1-methylnaphthalene and cyclopentene as triplet quenchers; in the latter case, formation of photoadducts was observed to compete with formation of methanol adducts.Quenching rate constants were determined by laser flash studies. - Key words: laser flash photolysis, kinetic absorption spectroscopy (KAS), photoacoustic calorimetry (PAC), protonation of triplet states, trans-cyclohexenones.
