Design of a chiral mesoporous silica and its application as a host for stereoselective di-pi-methane rearrangements.
[reaction: see text] A chiral periodic mesoporous organosilica (ChiMO) was prepared, in which a 1,2-bis-(ureido)cyclohexyl linker (38 wt %) is introduced into the walls of the hybrid organic-inorganic material. This silica was used as a host for 11-formyl-12-methyldibenzobarrelene (2), and the stereoselectivity of the di-pi-methane rearrangement of 2 within this host-guest complex was studied. At low conversions, the only product was the corresponding dibenzosemibullvalene. An enantiomeric excess of 24% at 11% conversion was obtained using the ChiMO as host. These values compare well with those achieved using a system based on conventional faujasites (LiY and NaY) as hosts incorporating a chiral auxiliary. We tested S-phenylglycine, S-proline, S-camphanic acid, and S-mandelic acid as chiral auxiliaries. In contrast to the behavior of the ChiMO material, adsorption of dibenzobarrelene in purely siliceous mesoporous MCM-41 silica (3.2 nm pore size) containing ephedrine failed, a failure that can be explained as arising from the large internal silanol population and high hydrophilicity of the siliceous MCM-41 sample.
Benitez
Miriam
M
Instituto de Tecnología Química CSIC-UPV, Av. De los Naranjos, s/n, 46022 Valencia, Spain.
Bringmann
Gerhard
G
Dreyer
Michael
M
Garcia
Hermenegildo
H
Ihmels
Heiko
H
Waidelich
Michael
M
Wissel
Kathrin
K
D008697:Methane / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D017646:Organosilicon Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D016062:Porosity; D012822:Silicon Dioxide / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism
D017646:Organosilicon Compounds; D012822:Silicon Dioxide; D008697:Methane