Chiral Memory in Silyl-Pyridinium and Quinolinium Cations

Abstract

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Chiral Chalcogenyl‐Substituted Naphthyl‐ and Acenaphthyl‐Silanes and Their Cations

“…For this purpose we followed the chiral memory strategy developed by Landais and co-workers. [36,37] The enantiomerically enriched silanes 3a, 4a und 9 were treated with trityl borate. The resulting silyl borates 13 a, 13 c and 14 a[B(C 6 F 5 ) 4 ]w ere subsequently reduced to regenerate the precursor silanes.…”

“…Landais and coworkers observed as imilard ecisive influence of strain on the configurational stabilityo fc hiral silicon centers in their recent study on pyridyl-and quinoline-stabilized chiral silyl cations VI and VII. [37] Recently,o ur group developed an experimental acidity scale for the assessment of the Lewis acidity of intramolecularly stabilizeds ilyl cations using para-fluorobenzonitrile (FBN) as a NMR chemical shift probe. [39] This method relies on the fact, that coordination of the nitrile to the silicon atom does not cancel the intramolecular interaction of the donor group with the silicon atom.…”

“…Chiral silyl cations synthesized by the groups of Oestreich and Landais. [27,28,32,36,37] [a] Dr.S. Künzler catalyzes challenging Diels-Alder reactions at low temperatures in good yields and decent enantioselectivities (up to 81 % ee).…”

“…[34,35] The question whether the stereochemical information at the silicon atom is retained by the neighboring group effect of an electron-donating group during the typicali onization/nucleophilic addition sequenceo fs ilylium ion catalysis was recently addressed by Landais, Roberta nd co-workers. [36,37] They showed in their chiral memory experiments for the intramolecularly stabilized silyl cations V-VII that during the completes ilyl cation formation/hydride addition reactions equence the stereochemistry at the silicona tom is controlled by the anchimeric assistance of the oxygen or nitrogen donors. We recently investigated silyl chalconium ions VIII (R 1 = R 2 = Me) based on the rigid peri-naphthyl and peri-acenaphthyl skeleton ( Figure 2).…”

“…Finally,t he conservation of the stereochemistry at the chiral silicon atom througha nchimeric assistance by the chalcogenyl group was tested applying the silicon cation formation/hydride addition sequence suggested by Landaisa nd Robert. [36,37]…”