A Rh(II)-catalyzed cycloaddition approach towards the synthesis of komaroviquinone.

Using a rhodium(II)-catalyzed cyclization/cycloaddition sequence as the key reaction step, the icetexane core of komaroviquinone was constructed by an intramolecular dipolar-cycloaddition of a carbonyl ylide dipole across a tethered pi-bond. The ylide was arrived at by cyclization of a rhodium carbenoid intermediate onto a proximal ester group. Efforts towards the preparation of the required precursor for elaboration to the natural product are discussed.

A general synthetic entry to the pentacyclic strychnos alkaloid family, using a [4 + 2]-cycloaddition/rearrangement cascade sequence.

The total synthesis of (+/-)-strychnopivotine, (+/-)-tubifolidine, (+/-)-strychnine, and (+/-)-valparicine is reported. The central step in the synthesis consists of an intramolecular [4 + 2]-cycloaddition/rearrangement cascade of an indolyl-substituted amidofuran that delivers an aza-tetracyclic substructure containing the ABCE-rings of the Strychnos alkaloid family. A large substituent group on the amide nitrogen atom causes the reactive s- trans conformation of the amidofuran to be more highly populated, thereby facilitating the Diels-Alder cycloaddition.

N-sulfonyloxy carbamates as reoxidants for the tethered aminohydroxylation reaction.

The use of N-sulfonyloxy carbamates as reoxidants for the tethered aminohydroxylation (TA) reaction is reported. These new conditions obviate the requirement for lithium hydroxide and tBuOCl in the oxidation mixture. In addition to providing aminohydroxylation products in good yields, the catalyst loadings can be reduced to just 1 mol % osmium.

Stereospecific synthesis of 1,2-cis glycosides by vinyl-mediated IAD.

[reaction: see text] Stereospecific 1,2-cis glycosylation of 2-O-vinyl thioglycosides, synthesized from the corresponding alcohols by Ir-catalyzed transvinylation with vinyl acetate, is achieved by iodine-mediated tethering of a range of primary and secondary carbohydrate acceptors, followed by intramolecular aglycon delivery (IAD). The use of such an intramolecular glycosylation strategy furnishes the desired alpha-gluco and beta-manno disaccharides in an entirely stereoselective manner.