89593-89-5Relevant academic research and scientific papers
Formation of carbocycles by intramolecular conjugate displacement: Scopeand mechanistic insights
Wang, Lihong,Prabhudas, Bodhuri,Clive, Derrick L. J.
supporting information; scheme or table, p. 6003 - 6012 (2009/09/25)
A detailed study has been made of a method of ring closure categorized as an all-carbon intramolecular conjugate displacement (ICD). This reaction involves intramolecular addition of a carbanion, which is stabilized by at least one electron-withdrawing group, to a Michael acceptor which has a leaving group in an allylic position. The process formally resembles a combination of Michael addition and S N2' displacement. The overall result is formation of a ring with loss of the allylic leaving group and shift of the original double bond to a new location spanning the positions of the electron-withdrawing substituent of the Michael acceptor subunit and the original allylic leaving group. The starting materials are easily prepared by a selenium-based version of the Morita-Baylis-Hillman reaction. The cyclizations are transition metal free and occur under mild conditions, using DBU or Cs 2CO 3 inMeCN or THF. Acetate is a suitable leaving group and the electron-withd rawing substituent of the Michael acceptor unit can be CO 2R,SO 2Ph, or CN. Six- and seven-membered rings are formed effi ciently, and complex structures, such as those resembling the core of CP-225,917, are easily assembled. The products of these ICD reactions are themselves classical Michael acceptors. A range of mechanisms probably operates, depending on the structure of the starting material and the reaction conditions, but conclusive evidence for a stepwise mechanism was obtained in a suitably biased case, while other observations are compatible with a concerted process or a stepwise path involving a short-lived carbanion that evades capture by a proton source.
Elimination and Addition Reactions. Part 40. The Insignificant Effect of Strain in Higher Order Eliminations in 1,1-bis(phenylsulphonyl) Carbanions with ω-Leaving Groups
Benedetti, Fabio,Stirling, Charles J.M.
, p. 605 - 612 (2007/10/02)
Rates of cyclisation of 1,1-bis(phenylsulphonyl) carbanions bearing distal leaving groups have been determined.The response of the system to solvent effects and to leaving group is similar to that in intramolecular nucleophilic substitution.The system is
Activation Parameters for Intramolecular Nucleophilic Substitution by Carbanions - the Insignificant Effect of Ring Strain on Cylisation Rates
Benedetti, Fabio,Stirling, Charles J. M.
, p. 1374 - 1376 (2007/10/02)
Activation parameters for the cyclisation of bis-sulphonyl-stabilised carbanions to bis-sulphonylcycloalkanes have been determined; cyclopropanes form nearly a million-fold faster than cyclobutanes and ring strain is a negligible factor in determining rea
