Highly Enantioselective [2+2]-Cycloaddition Reactions Catalyzed by a Chiral Aluminum Bromide Complex
作者:Eda Canales、E. J. Corey
DOI:10.1021/ja0765262
日期:2007.10.1
Enantioselective [2+2]-cycloaddition pathways to chiral cyclobutanes are rare and not generally utilized for synthesis. A new cycloaddition reaction of vinyl ethers with trifluoroethyl acrylate in the presence of a catalytic amount of chiral oxazaborolidine−AlBr3 complex is described which affords [2+2]-adducts with excellent yields and enantioselectivities. Applications of these adducts to the synthesis
Formal (3+3) Cycloaddition of Silyl Enol Ethers Catalyzed by Trifric Imide: Domino Michael Addition-Claisen Condensation Accompanied with Isomerization of Silyl Enol Ethers
作者:Takumi Azuma、Yoshiji Takemoto、Kiyosei Takasu
DOI:10.1248/cpb.59.1190
日期:——
We describe here a Tf₂NH-catalyzed formal (3+3) cycloaddition of silyl enol ethers with acrylates as a new domino reaction. In the domino sequence, the catalyst activates Michael addition, deprotonation of the resulting silyloxonium cation and intramolecular Claisen condensation. It was found that reaction modes significantly depend on the reaction temperature. We also examined the mechanistic detail
The isomerization of siloxycyclopropanes to enol silylethers and allylsilylethers was accomplished by using [Rh(CO)2Cl]2 as a catalyst. Regiochemistry with respect to the newly formed double bond of the product was highly dependent on the substitution pattern of cyclopropane ring.
A triflic imide (Tf(2)NH) catalyzed isomerization of kinetically favourable silyl enol ethers into thermodynamically stable ones was developed. We also demonstrated a one-pot catalytic reaction consisting of (2 + 2) cycloaddition and isomerization. In the reaction sequence, Tf(2)NH catalyzes both of the reactions.
Development of a novel synthetic method for medium‐sized trans‐cycloalkenes (TCAs) is described. Functionalized TCAs are readily prepared from simple cycloalkanones in a few steps, namely, enol silyl ether formation, [2+2] cycloaddition, and domino 4π electrocyclic ring opening/alkylation (conjugate addition). The first example of central‐to‐planar chirality transfer from enantiomerically enriched