Aprocess for the assembly of carbazole alkaloids has been developed on the basis of ring-closing metathesis (RCM) and ringrearrangement-aromatization (RRA) as the key steps. This method is based on allyl Grignard addition to isatin derivatives to provide smooth access to 2,2-diallyl 3-oxindole derivatives through a 1,2-allyl shift. The diallyl derivatives were used as RCM precursors to afford a novel class of spirocyclopentene-3-oxindole derivatives, which underwent a novel RRA reaction to afford carbazole derivatives. The synthetic sequence to carbazoles was shortened by combining the RCM and RRA steps in an orthogonal tandem catalytic process. The utility of this methodology was further demonstrated by the straightforward synthesis of carbazole alkaloids, including amukonal derivative, girinimbilol, heptaphylline, and bis(2-hydroxy-3-methylcarbazole).

„Der Teil meines Berufs, den ich am meisten schätze, ist junge Menschen zu motivieren, zu unterstützen und zu bilden. Das größte Problem, dem Chemiker gegenüberstehen, ist die Bedeutung und Schönheit der Naturwissenschaften deutlich zu machen …︁“ Dies und mehr von und über Albert Schenning finden Sie auf Seite 6628.

Click" chemistry is combined with organocatalysis to fabricate a multifunctional C 3 -symmetrical dendritic prolinamide with a hydrophobic aromatic core and hydrophilic triazolinium arms that exhibit high efficiency in catalyzing the asymmetric aldol reaction with cyclic ketones. The catalyst is water-compatible and remains active for five consecutive catalytic runs with a low catalyst loading (2 mol%), yielding the aldol products in high yields, diastereo-and enantioselectivities.

The first organocatalytic enantioselective approach to precursors of tubuvaline (pre-Tuv) is presented employing a prolinamide-catalyzed aldol reaction of easily accessible thiazole-carbaldehyde with methyl isopropyl ketone "on water" in excellent yield as well as regio-and enantioselectivities. The analogues of pre-Tuv were achieved using an lproline-catalyzed direct asymmetric aldol reaction of substituted thiazole-carbaldehydes with acetone. A direct and flexible approach to the tubavaline (Tuv) core of tubusylins has been established employing the reductive amination of the pre-Tuv species. The key aldol reaction should greatly expand the potential of this strategy to the synthesis of natural product tubulysins and a range of analogues.Scheme 2. Synthesis of tubuvaline analogues.

Aprocess for the assembly of carbazole alkaloids has been developed on the basis of ring‐closing metathesis (RCM) and ringrearrangement–aromatization (RRA) as the key steps. This method is based on allyl Grignard addition to isatin derivatives to provide smooth access to 2,2‐diallyl 3‐oxindole derivatives through a 1,2‐allyl shift. The diallyl derivatives were used as RCM precursors to afford a novel class of spirocyclopentene‐3‐oxindole derivatives, which underwent a novel RRA reaction to afford carbazole derivatives. The synthetic sequence to carbazoles was shortened by combining the RCM and RRA steps in an orthogonal tandem catalytic process. The utility of this methodology was further demonstrated by the straightforward synthesis of carbazole alkaloids, including amukonal derivative, girinimbilol, heptaphylline, and bis(2‐hydroxy‐3‐methylcarbazole).