3718-56-7Relevant articles and documents
Bismuth-substituted "sandwich" type polyoxometalate catalyst for activation of peroxide: Umpolung of the peroxo intermediate and change of chemoselectivity
Amanchi, Srinivasa Rao,Khenkin, Alexander M.,Diskin-Posner, Yael,Neumann, Ronny
, p. 3336 - 3341 (2015/06/16)
The epoxidation of alkenes with peroxides by WVI, MoVI, VV, and TiIV compounds is well established, and it is well accepted that the active intermediate peroxo species are electrophilic toward nucleophilic substrates. Polyoxotungstates, for example, those of the "sandwich" structure, [WZn(TM-L)2(ZnW9O34)2]q- in which TM = transition metal and L = H2O, have in the past been found to be excellent epoxidation catalysts. It has now been found that substituting the Lewis basic BiIII into the terminal position of the "sandwich" polyoxometalate structure to yield [Zn2BiIII2(ZnW9O34)2]14- leads to an apparent umpolung of the peroxo species and formation of a nucleophilic peroxo intermediate. There are two lines of evidence that support the formation of a reactive nucleophilic peroxo intermediate: (1) More electrophilic sulfoxides are more reactive than more nucleophilic sulfides, and (2) nonfunctionalized aliphatic alkenes and dienes showed ene type reactivity rather than epoxidation pointing toward "dark" formation of singlet oxygen from the nucleophilic intermediate peroxo species. Allylic alcohols reacted much faster than alkenes but showed chemoselectivity toward C-H bond activation of the alcohol and formation of aldehydes or ketones rather than epoxidation. This explained via alkoxide formation at the BiIII center followed by oxidative β-elimination.
Use of the Ketal Claisen Rearrangement for the Synthesis of Cyclic Sesquiterpenes Containing Quaternary Centers. A Formal Synthesis of Cuparene.
Schuda, Paul Francis,Potlock, Steven J.,Ziffer, Herman
, p. 463 - 468 (2007/10/02)
We have shown that the ketal based Claisen rearrangement can be useful for generating vicinal quaternary and tertiary-quaternary centers by suitable substitution on the reacting 2-cyclohexenols and cycloalkanone ketal.A rapid and efficient method for preparing hindered cycloalkanone ketals in very pure form is presented, as well as a useful modification for synthesizing the requied 2-cyclohexenols from alkyl anisoles with a minimum number of undesired side products.
Origins of Regio- and Stereoselectivity in Additions of Phenylselenenyl Chloride to Allylic Alcohols and the Applicability of These Additions to a Simple 1,3-Enone Transposition Sequence
Liotta, Dennis,Zima, George,Saindane, Manohar
, p. 1258 - 1267 (2007/10/02)
The regio- and stereoselectivity of phenylselenenyl chloride additions to allylic alcohols and their derivatives have been systematically studied.On the basis of the results, a mechanism involving two basic premises is proposed.These are as follows: (a) allylic oxygen's direct selenonium ion formation to the syn face of the double bond; (b) axial attack of the chloride ion is kinetically favored over equatorial attack.A series of rules which are useful for predicting the regio- and stereoselectivity of phenylselenenyl chloride additions to allylic systems are discussed.In addition, these reactions can be used as the key step in a general 1,3-enone transposition sequence.Several examples of this transposition sequence are illustrated.
