Asymmetric deprotonation and complexation reactions mediated by chiral ketals as a route to ortho-disubstituted (.eta.6-arene)Cr(CO)3 complexes
摘要:
A series of chiral ketals derived from an aryl ketone or aldehyde and one of several C2-symmetrical diols were converted to their corresponding (eta-6-arene)Cr(CO)s complexes. The resultant 1,3-dioxolanes were trans substituted at C-4 and C-5 by groups CH2X, where X = H (1), OCH3 (2), or N(CH3)2 (3). Ortho deprotonation was attempted on complexes 1-3 using tert-butyllithium in THF solution to afford the corresponding lithio derivatives, which were treated with a variety of electrophiles (MeOSO2F, TMSCl, Ph2C(O), Ph2PCl). Although 1 gave a complex mixture of products, complexes 2 and 3 afforded good yields of disubstituted complexes (with the exception that the lithiated derivative of 3 did not undergo methylation when treated with MeOSO2F). The stereoselectivity of the reactions was determined by NMR spectroscopy and found to be in the range of 3:1 for 2 and >9.1 for 3. The sense of diastereoselection were identified by chemical correlations (for compounds derived from 2) and by circular dichroism spectroscopy. Poor diastereoselection was obtained when this protocol was performed on the corresponding acetal ultimately derived from benzaldehyde and N,N,N',N-tetramethyl-1,4-diamino-2,3-butanediol. In addition, a related series of ortho-disubstituted arenes bearing chiral ketal or acetal substituents in the benzylic position were subjected to complexation reactions with (naphthalene)Cr(CO)3 in dibutyl ether. The best diastereoselectivity observed with this methodology was 48%, obtained with the acetal derived from o-tolualdehyde and N,N,N',N-tetramethyltartramide.
Pd(II)-Catalyzed Conversion of Styrene Derivatives to Acetals: Impact of (−)-Sparteine on Regioselectivity
摘要:
Pd[(-)-sparteine]Cl-2 catalyzes the formation of dialkyl acetals from styrene derivatives with Markovnikov regioselectivity. The substrate scope of this reaction has been investigated, and initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd-hydride.
Cyclopentene Assembly by Microwave-Assisted Domino Reaction of Donor–Acceptor Cyclopropanes with Ketals
作者:Hung M. Nguyen、Hemender R. Chand、Nikita E. Golantsov、Igor V. Trushkov、Leonid G. Voskressensky
DOI:10.1055/s-0039-1690775
日期:2020.2
A Lewis acid-mediated domino reaction of acetalsderivedfrom aromatic ketones with 2-(het)arylcyclopropane-1,1-diesters has been developed. The reaction provides a convenient approach to cyclopentenes and related polycyclic ring systems.
A textile finishing composition comprising a silylated polyether, a compound selected from aldehydes, acetals and mixtures thereof and a diluent. The textile finishing composition is applied to textile materials to impart improved dimensional stability, improved wetting properties and a durable softness.
Pd(II)-Catalyzed Conversion of Styrene Derivatives to Acetals: Impact of (−)-Sparteine on Regioselectivity
作者:Amy M. Balija、Kara J. Stowers、Mitchell J. Schultz、Matthew S. Sigman
DOI:10.1021/ol053110p
日期:2006.3.1
Pd[(-)-sparteine]Cl-2 catalyzes the formation of dialkyl acetals from styrene derivatives with Markovnikov regioselectivity. The substrate scope of this reaction has been investigated, and initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd-hydride.