Asymmetric [2 + 2] cycloaddition reaction catalyzed by a chiral titanium reagent
摘要:
In the presence of certain Lewis acids, alkenes containing an alkylthio group (for example, ketene dithioacetals, alkenyl sulfides, alkynyl sulfides, and allenyl sulfides) react with electron deficient olefins to give the corresponding cyclobutane, cyclobutene, or methylene cyclobutane derivatives. By employing a chiral titanium catalyst generated in situ from dichlorodiisopropoxytitanium and a tartrate-derived chiral diol, the [2 + 2] cycloaddition reaction proceeds with high enantioselectivity.
The EtAlCl<sub>2</sub>-Catalyzed Cargill Rearrangement of Bicyclo[n.2.0] Compounds Prepared by the [2+2] Cycloaddition of Cycloalkenones and 1-<i>t</i>-Butyldimethylsilyl-2-methylthioacetylene
EtAlCl2 catalyzes the Cargill rearrangement of bicyclo[n.2.0] compounds which were prepared by the TiCl4-mediated [2+2] cycloaddition reaction of cycloalkenones and 1-t-butyldimethylsilyl-2-methylthioacetylene, yielding various bicyclo[n-1.2.1] compounds under mild reaction conditions.