Hydroxygardnerine, Hydroxygardnutine, Gardnerine, (E)-16-epi-Normacusine B, and Koumine syntheses

Hiromitsu Takayama and co-workers from Chiba University have reported in Organic Letters on the syntheses of some indole alkaloids using a gold catalyzed 6-exo dig cyclization – which looks like a Conia-ene reaction.

 

OL paper

Gomerone C synthesis

Erick Carreira and co-worker have reported in ACIE on the synthesis of gomerone C.

ACIE paper

Ag/La mediated Conia-ene

Masakatsu Shibasaki and co-workers at the University of Tokyo have reported in ACIEE on a silver/lanthanum catalyzed Conia-ene reaction.

ACIEE paper

Copper/amine cooperative catalysis

Veronique Michelet and co-workers from CNRS have reported in the European Journal of Organic Chemistry on a copper/amine cooperative catalyzed Conia-ene type reaction.

European JOC paper

A Cool Cascade

Chi-Sing Lee and co-workers at Peking University have published in Organic Letters on a cascade reaction that leads to 5,6-bicyclic rings.  This reaction catalyzed by zinc (II) bromide involves a Diels-Alder reaction followed by a reaction that looks like the Conia-ene reaction.

 

OL paper

Zn/Yb-Mediated Conia-Ene Reaction

Jin-Heng Li and co-workers from Hunan Normal University have published in Synthesis on a Conia-ene reaction using Yb and Zn.  This reaction is catalytic in zinc but stoichiometric in ytterbium.  When a terminal alkyne is used, the cyclization is in the exo-dig mode, but when an internal alkyne is used, the cyclization is in the endo-dig mode.

Synthesis paper

Indium-Catalyzed Cyclization

Virginie Ratovelomanana-Vidal and co-workers at Chimie ParisTech have published in Organic Letters on what looks like an indium promoted Conia-Ene cyclization.

OL paper

A Michael/Conia-ene Cascade Reaction

There are a lot of biologically active compounds out there with 5,7-bicyclic ring systems and because of these compounds exist, many different approaches for obtaining 5,7-ring systems are attempted.  Chi-Sing Lee and co-workers at Peking UniVersity Shenzhen Graduate School have recently published in Organic Letters on the synthesis of clavukerin A, a natural product that possesses this 5,7-bicyclic ring system.  The carbon skeleton is interesting, but I have to admit that the new reaction that was developed is even more interesting!  The starting substrate is an alpha,beta-ketone activated with an electron withdrawing group on the alpha position with an alkyne and an aldehyde.  Basically, they use a secondary amine (diethylamine) to do some enamine chemistry – specifically, a Michael addition of the aldehyde onto the enone and then with the presence of zinc (II) iodide, a Conia-ene reaction occurs to form the five membered ring.

OL paper