Reversal of Chemoselectivity in Organotin Lewis Acid-Catalyzed Reaction of Ketene Silyl Acetal with Aldehyde and α-Enal
作者:Jianxie Chen、Junzo Otera
DOI:10.1055/s-1997-715
日期:——
The organotin Lewis acid-catalyzed reaction of ketene silyl acetal with aldehydes results in reversal of chemoselectivity: α-enals react preferentially or exclusively in competition with an alkanal or even aromatic aldehydes.
β,β-Dimethyl-substituted ketenesilylacetal (1a) reduces p-chloranil and other activated quinones with electron-withdrawing substituents to produce the carbon–oxygen adduct, the hydrolysis of which yields the corresponding hydroquinone ether. The structure of the hydroquinone ether has been determined by the X-ray crystal analysis. The reactions are significantly slowed down in benzene where the charge-transfer
Conjugated imines and iminium salts as versatile acceptors of nucleophiles
作者:Makoto Shimizu、Iwao Hachiya、Isao Mizota
DOI:10.1039/b814930e
日期:——
development of synthetic methodologies where nucleophilicaddition reactions to imino carbons are utilized in crucial steps. This article summarizes double nucleophilicaddition reactions with alpha,beta-unsaturated aldimines, addition reactions using alkynyl imines, "umpoled" reactions of alpha-imino esters, and the use of iminium salts as reactive electrophiles.
Organotin perchlorates as gentle Lewis acid catalysts in Mukaiyama reaction
作者:Jian-xie Chen、Junzo Otera
DOI:10.1016/s0040-4020(97)00995-2
日期:1997.10
aldehydes, an electron-donating group increases the reactivity of aldehyde while the reverse is true with an electron-withdrawing group. These are opposite to the reactivity order in nucleophilic addition to free carbonyls. In contrast to ketene silyl acetal, enol silyl ethers derived from ketones are not activated by organotin perchlorates. Thus, these two enol silyl ethers can be discriminated from each
these reactions. Enhanced preference for the more sterically demanding Michael adducts is obtained with Bu(2)Sn(OTf)(2), SnCl(4), and Et(3)SiClO(4) in the former reaction while TiCl(4) gives the highest selectivity for the less sterically demanding products in the latter case. These results are interpreted in terms of alternative reaction mechanisms. The reaction of less bulky ketene silyl acetals are