Chemistry of Dioxacyclanes: XI. Synthesis and Properties of Unsaturated Derivatives of 1,3-Dioxolanes
摘要:
1,3-Dioxolanes were synthesized by reactions of 3-cyclohexenecarboxaldehyde and 5-norbornene2-endo-carboxaldehyde with 1,2-ethanedithiol and 3-(2-propenyloxy)- and 3-propoxy-1,2-propanediols, as well as of propionaldehyde, benzaldehyde, and trichloroacetaldehyde with the latter two thiols. Dichlorocarbene addition, bromination, and epoxidation of the ring C=C were accomplished, and activity of the resulting products as dienophiles in Dield-Alder reactions was assessed.
The first asymmetricchiral N-triflylphosphoramide-catalyzed ionic [2+4] cycloaddition reaction of unsaturated acetals is described. This reaction proceeds through the intermediacy of a vinyl oxocarbenium/chiral anion pair, and the chiral N-triflylphosphoramide anion controls the stereoselectivity of the cycloaddition step. Moderate enantioselectivities (up to 80:20 e.r.) have been obtained when α