A new alkylation method of acetals has been developed by the reaction of the cationic intermediates, obtained by TESOTf-2,4,6-collidine treatment of acetals, followed by a Gilman reagent. The feature of the method is high chemoselectivity, which could not be attained by previously reported methods. Reaction proceeds under weakly basic conditions that acid-labile functional groups can tolerate.
developed a chemoselective deprotection and nucleophilic substitution of acetals from aldehydes in the presence of ketals. This article describes the highly discriminative and chemoselective transformations of acetals bearing different substitution patterns, different types of acetals, as well as mixed acetals. These reactions can achieve the transformations that cannot be attained by conventional methods,
Organic Chemistry Using Weakly Electrophilic Salts: Efficient Formation of <i>O</i>,<i>O</i>-Mixed, <i>O</i>,<i>S</i>- and <i>N</i>,<i>O</i>-Acetals
作者:Hiromichi Fujioka、Takashi Okitsu、Takuya Ohnaka、Ruichuan Li、Ozora Kubo、Kazuhisa Okamoto、Yoshinari Sawama、Yasuyuki Kita
DOI:10.1021/jo071187g
日期:2007.10.1
A mild and efficient method for the preparation of O,O-mixed, O,S- and N,O-acetals from symmetrical O,O-acetals has been developed. Thus, the treatment of symmetrical O,O-acetals with TESOTf and 2,4,6-collidine formed weakly electrophilic collidinium salts. The addition of nucleophiles, such as an alcohol, lithium thioxide, and sodium azide, to the salts afforded the corresponding O,O-mixed, O,S- and N,O-acetals in good yields. The reaction proceeded under weakly basic conditions. No overreaction then occurred and many acid-labile functional groups could remain intact.
Organic Chemistry Using Weakly Electrophilic Salts: The Reaction with Nitrogen Nucleophiles
The reaction of electrophilic salts, which were obtained by the treatment of acetals with TESOTf*center dot 2,4,6-collidine, with nitrogen nucleophiles was studied in detail. Treatment of the salts with potassium phthalimide afforded the corresponding N,O-acetals in good yields. The use of hydrazine in place of potassium phthalimide gave the corresponding hydrazones. The reaction is very mild and chemoselective, and acid-labile functional groups can tolerate these conditions.