Enolonium Species-Umpoled Enolates.

Enolonium species/iodo(III)enolates of carbonyl compounds have been suggested to be intermediates in a wide variety of hypervalent iodine induced chemical transformations of ketones, including α-C-O, α-C-N, α-C-C, and α-carbon-halide bond formation, but they have never been characterized. We report that these elusive umpoled enolates may be made as discrete species that are stable for several minutes at -78 °C, and report the first spectroscopic identification of such species. It is shown that enolonium species are direct intermediates in C-O, C-N, C-Cl, and C-C bond forming reactions.

Oxidative asymmetric umpolung alkylation of Evans' β-ketoimides using dialkylzinc nucleophiles.

Umpolung alkylation of Evans' auxiliary substituted β-ketoimides affords the diastereomerically pure products in yields ranging from 40 to 80%. The reaction itself proceeds with diastereoselectivities between 3 : 1 and 18 : 1. Dialkylzinc serves as the nucleophile and umpolung of the β-keto-imide enolate is achieved by the action of Koser's reagent.

A new strategy for the synthesis of crucigasterin A, and cytotoxic activity of this compound and its related analogues.

Stereoselective total synthesis of bioactive marine natural product crucigasterin A has been accomplished from commercially available and inexpensive L-(-)-malic acid as a starting material. Julia olefination and chelation controlled Grignard additions are the key steps involved in the present synthesis. Cytotoxic properties of crucigasterin A and its related analogues crucigasterins B and D have been evaluated.