Naturalproductman’s Blog

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Archive for July, 2009

Nitrone-Ketene Coupling

Posted by naturalproductman on July 31, 2009

Andrew Smith and co-workers at the University of St. Andrews in the UK have recently published in Organic Letters where they have reported on a reaction cascade that involves a nucleophilic addition of the nitrone onto the ketene followed by a 3,3-sigmatropic rearrangement to eventually form an oxindole.  The reaction takes place in a dry ice bath temperature and the ketene is formed in-situ from an acid chloride with triethylamine.
ketene nitrone

OL paper

Posted in Cascade Reactions, Cycloaddition, Methodology, Sigmatropic Rearrangements | Leave a Comment »

Neodymium Chemistry

Posted by naturalproductman on July 31, 2009

Min Shi and co-worker from the Shanghai Institute of Organic Chemistry have recently published in the European Journal of Organic Chemistry on an intermolecular coupling reaction between an allenyl cyclopropane and an enynol using a Nd catalyst.  It results in the formation of a 5,7,6-fused tricycle that shares the carbon cyclic backbone with a famous antibiotic, guanacastapene.

neodymium

European Journal of Organic Chemistry

Posted in Allenes, Cascade Reactions, Methodology, Ring expansion, Ring forming, Ring Opening | Leave a Comment »

The Novelty of an Olefin Metathesis Reaction

Posted by naturalproductman on July 31, 2009

Subrata Ghosh and co-workers at the Indian Association for the Cultivation of Science have recently published their progress toward a natural product, Caribenol A in Tetrahedron Letters.  It’s a very interesting entry to making 5,7-bicyclic rings.  I know that olefin metathesis is becoming very common and not as exciting and novel but the olefin metathesis they did in this case involved the opening of the norbornene derivative that gave rise to the five membered ring.

olefin metathesis

TL paper

Posted in Methodology, Ring forming, Seven-Membered Rings, Transition Metal | Leave a Comment »

Platensimycin Studies

Posted by naturalproductman on July 31, 2009

Sheo Singh and co-workers at Merck have recently published in Tetrahedron Letters on the interaction of platensimycin with the enzyme FabF, an enzyme found in the fatty acid biosynthetic pathway.  Inhibition of these classes of enzymes leads to the compound’s antibiotic activity.  They even have a co-crystal structure reported in the paper between the molecule and the enzyme.

platensimycin

Nature paper

TL paper

Posted in Antibiotics, Mechanistic | Leave a Comment »

Four Component Reaction

Posted by naturalproductman on July 30, 2009

Shu-Jiang Tu (Xuzhou Normal University and Suzhou University) and coworkers in collaboration with Guigen Lee (Texas Tech) and co-workers have recently published in JACS on a four component reaction that involves the combining of an aldehyde, ketone and two cyanoamides to form tricyclic 5,6,6-rings that look like alkaloid type molecules. It’s a simple protocol that requires microwave heating at 120 degrees celsius for 12 min in the presence of 1 equivalent of potassium carbonate.

microwave mcc

JACS article

Posted in Cascade Reactions, Cycloaddition, Methodology, Multi-Component Coupling, Ring forming | Leave a Comment »

A Five Component Reaction

Posted by naturalproductman on July 29, 2009

Carlos Marcos et al at the Universidad de Extremadura have recently published on a five component coupling reaction in JOC.  Well, basically it’s an Ugi followed by condensation with an amine to form a spiropyrrolidinochromanone.  Ugi reactions normally consist of an aldehyde or ketone, isocyanide, amine and carboxylic acid.  The special type of Ugi reaction we see here has an aldehyde with extra functionality – a chromone moiety.

5 component reaction

JOC paper

Posted in Methodology, Multi-Component Coupling | Leave a Comment »

Uncialamycin Progress

Posted by naturalproductman on July 29, 2009

Nicolau has already synthesized uncialamycin.  However, just because one person has completed the synthesis, it doesn’t mean there will be more elegant ways to access the same target molecule.  This enediyne natural product was isolated from a streptomycete isolated from the surface of a lichen, Cladonia uncialis.  It has interesting anti-tumor activities.  The highlight of the synthesis from Pierre van de Weghe from the Universite de Rennes in France is the intramolecular imino-alkyne diels alder to form a subsituted quinoline.  You can check out the synthesis in JOC.

uncialamycin
JOC paper

Posted in Cycloaddition, Enediynes, Methodology | Leave a Comment »

Ugi Reaction to Make Dihydrophenanthridines

Posted by naturalproductman on July 28, 2009

Last year, Jieping Zhu et al at CNRS published in nthe Beilstein Journal of Organic Chemistry on a four component Ugi reaction followed by an intramolecular C-H functionalization to form a diaryl C-C bond between an aryl halide and an aryl group.  Overall this is a useful method to make dihydrophenanthridines.

dihydrophenanthridines

BJOC paper

Posted in Aromatic, Methodology, Multi-Component Coupling, Ring forming, Transition Metal | Leave a Comment »

Ni Catalyzed Hydroacylation

Posted by naturalproductman on July 28, 2009

Michinori Suginome, Toshimichi Ohmura and co-workers from Kyoto University have recently published in JACS on a hydroacylation reaction catalyzed by Ni(c0d)2 (5 mol%) to potentially yield quaternary centers.  The substrate they reacted the aldehyde with was a vinyl cyclopropane which opened on the saturated end.

ni reaction

JACS paper

Posted in Methodology, Ring Opening, Transition Metal | Leave a Comment »

Cascade Heck Reaction

Posted by naturalproductman on July 27, 2009

Yimin Hu et al at Anhui Normal University in China have recently published in Chemical Communications on a Heck-cascade reaction that leads to five contiguous stereocenters.  It’s not only an intermolecular coupling between an aryl halide and an alpha-beta-unsaturated amide, but also a cyclization that leads to the formation of two new rings – it almost looks like a Diels-Alder reaction except that there is an extra functional group introduced.

heck cascade

Chem Comm paper

Posted in Cascade Reactions, cross coupling, Methodology, Ring forming, Transition Metal | 2 Comments »

 
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