Explorations on the asymmetric total synthesis of isoschizogamine.

Two approaches to the synthesis of isoschizogamine were reported. Both routes utilized an efficient aza-Claisen rearrangement to establish the absolute stereochemistry of the all-carbon quaternary center in the natural product. In the first approach, a highly diastereoselective (10:1) hetero-Diels-Alder reaction was utilized to reach a densely functionalized tetrahydroquinoline derivative as an advanced intermediate to the targeted alkaloid. An acylamidine intermediate was prepared and studied in the intramolecular cyclization reaction under acidic conditions in our second approach.

Phosphine-mediated coupling of gramines with aldehydes: a remarkably simple synthesis of 3-vinylindoles.

A new and practical synthesis of terminally substituted 3-vinylindoles is described involving tributylphosphine-mediated coupling of gramines with aldehydes.

Chemoselective cyclizations of divinyl ketones to cyclohexenones mediated by Lewis acid and base.

[reaction: see text] Chemoselective cyclizations of divinyl ketones to cyclohexenones mediated by a sterically demanding Lewis acid and an amine base have been accomplished under mild reaction conditions. The extension of this methodology to the synthesis of eight-membered rings is also demonstrated.

Remarkably facile hexatriene electrocyclizations as a route to functionalized cyclohexenones via ring expansion of cyclobutenones.

This Communication describes a cascade reaction sequence that leads to highly functionalized cyclohexenones starting from reaction of cyclobutenones with alpha-lithio-alpha,beta-unsaturated sulfones and amides. The hexatriene-cyclohexadiene cyclization steps presumed to be involved in these transformations are among the most facile hexatriene electrocyclizations reported thus far.

Efficient construction of cyclopenta[b]quinoline core of isoschizozygane alkaloids via intramolecular formal hetero-Diels-Alder reaction.

[reaction: see text] Acid-catalyzed condensation of aromatic amines with delta,epsilon-unsaturated aldehydes, followed by intramolecular formal hetero Diels-Alder reaction, is described as a potential route to the cyclopenta[b]quinoline substructure of isoschizozygane alkaloids. Reactions are highly diastereoselective and produce adducts with up to four contiguous stereocenters.