Natural cis-trikentrin B was synthesized enantioselectively using, as key steps, an intramolecular Diels-Alder reaction of an allenic dienamide followed by aromatization to construct an indole ring and cleavage of bicyclo[2.2.1]heptene to launch a cis-dimethylcyclopentane ring. Diels-Alder adducts 9 and 10 were elaborated to provide allenic dienamide 25, and its intramolecular Diels-Alder reaction proceeded smoothly. Aromatization to an indole ring and stereoselective cleavage of the bicyclo[2.2.1]heptene ring were performed successfully. Introduction of an (E)-butenyl group via addition of propylmagnesium bromide and subsequent anti elimination of water gave natural cis-trikentrin B.

Optically active allene-1,3-dicarboxylates (1a and 2a), which contain the axial asymmetry of the allene moiety, were prepared. The Diels−Alder reaction of 1a and 2a with cyclopentadiene afforded the 1:1 (1a or 2a to cyclopentadiene) endo adducts 3a and 4a through the combination of the sterically favorable approach of the diene and the dienophile owing to the axial asymmetry of the allene moiety and the effective secondary orbital interaction. The absolute configurations of 3a and 4a were determined by chemical transformation and X-ray analysis. The absolute configuration of the axial asymmetry of 1a was also determined to be R by X-ray analysis.

No abstract

The enantioselective synthesis of (-)-cyclosarkomycin is accomplished using the endo 1 : 1 adduct of (R)-allene 1,3-dicarboxylate and cyclopentadiene.

No abstract