ChemInform Abstract: Preparation of Fused Tricycles Using Allylsilane‐Based “A + C → ABC” Annulation Strategies.

Majetich, George; Zhang, Y.; Nishide, Hiroyuki; Hull, Kenneth G.

doi:10.1002/chin.199552199

Cited by 1 publication

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“…The allylic silane 32d cyclized to 32e in the presence of TiCl 4 . Single experiments with 32d using BF 3 ·OEt 2 or Bu 4 NF were unsuccessful and were not examined further because of the high efficiency (90%) with which the desired closure occurred using TiCl 4 .…”

Section: Introductionmentioning

confidence: 99%

Formation of Carbocycles by Intramolecular Conjugate Displacement: Scope and Mechanistic Insights

2009

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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(N)2' 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(2)CO(3) in MeCN or THF. Acetate is a suitable leaving group and the electron-withdrawing substituent of the Michael acceptor unit can be CO(2)R, SO(2)Ph, or CN. Six- and seven-membered rings are formed efficiently, 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.

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Section: Introductionmentioning

confidence: 99%