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Archive for the ‘Ring contraction’ Category

This transformation involves making the ring smaller.

Ring size matters

Posted by naturalproductman on August 6, 2012

Petr Klan (Masaryk University) and Richard Givens (University of Kansas) have reported in JOC on a study of the photo-Favorskii rearrangement.

ring size

JOC paper

Posted in Cascade Reactions, Favorskii rearrangement, Light Mediated, Methodology, Named Reactions, Ring contraction | Leave a Comment »

Transannular Claisen rearrangement

Posted by naturalproductman on October 23, 2011

Donald Craig and co-workers at Imperial College have reported in Organic and Biomolecular Chemistry on a transannular Claisen rearrangement converting a lactone into a cyclobutane.

Claisen

OBC paper

Posted in Claisen rearrangement, Methodology, Named Reactions, Ring contraction | Leave a Comment »

Bi(OTf)3 mediated rearrangement

Posted by naturalproductman on March 1, 2011

Oliver Reiser and co-workers at Universitat Regensburg in Germany have reported in Organic and Biomolecular Chemistry on a bismuth (III) catalyst that rearranges tricyclic guaianolide rings.

rearrangement

OBC paper

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

Vinylogous Amides via Eschenmoser episulfide contractions

Posted by naturalproductman on March 1, 2011

Jan Bergman and co-workers have reported in JOC on an Eschenmoser episulfide contraction reaction to form vinylogous amides.

Eschenmoser

 

JOC paper

Posted in Cascade Reactions, Eschenmoser episulfide contraction, Mechanistic, Methodology, Ring contraction | Leave a Comment »

Ring Contraction via Iodination

Posted by naturalproductman on October 15, 2010

Dias and co-workers at the University of Missouri-Kansas City have published in Chemical Communications on an iodine promoted ring contraction of a C2-symmetric phen-diol.

iodination

 

Chem Comm paper

Posted in Cascade Reactions, Methodology, Ring contraction | Leave a Comment »

6 to 5 Ring Contraction

Posted by naturalproductman on July 5, 2010

Changing a steroid ring from the classical 6,6,6,5-carbon skeleton to a 6,6,5,6-carbon tetracycle can be a challenge, however, it appears to happen in nature with natural products such as cyclopamine and nakiterpiosin.  Athanassios Giannis and co-workers at the Universitat Leipzig in Germany have recently reported in JACS on a way to do such a transformation by using an 11-hydroxy steroid (hydroxy group in only the C-ring adjacent to the axial chiral methyl group)  and subjected to Comin’s reagent (2-[N,N-bis(trifluoromethanesulfonyl)amino]-5-chloropyridine), which is just a triflating agent, and DMAP in toluene under heated conditions to yield the 6 to 5 ring contraction product.

rearrangement

JACS paper

Posted in Cascade Reactions, Comin's, Methodology, Named Reagents, Ring contraction, Steroids | Leave a Comment »

Ring Contraction for Spirocyclic Centers

Posted by naturalproductman on June 21, 2010

Yoshiji Takemoto and co-workers at Kyoto University have published in Chemistry – A European Journal on a ring contraction protocol going from four to three membered rings.

ring contraction

Chemistry A European Journal paper

Posted in Cascade Reactions, Methodology, Ring contraction, Spirocyclic centers | Leave a Comment »

A Ring Contraction Approach for Taiwaniaquinone

Posted by naturalproductman on June 14, 2010

Karl Gademann and co-workers at the University of Basel in Switzerland have published in a ring contraction approach – an intramolecular benzilic acid rearrangement – to access the taiwaniaquinone carbon skeleton.

taiwaniaquinone

Chemistry – a European Journal paper

Posted in Cascade Reactions, Methodology, Ring contraction, Terpenes | Leave a Comment »

Bakkenolide Synthesis

Posted by naturalproductman on April 9, 2010

Luiz Silva and co-workers at the Universidade de Sao Paulo have recently reported in JOC on a ring contraction approach using TTN (thalium III nitrate) to synthesizing the five membered ring in bakkenolide.

ring contraction
JOC paper

Posted in Cascade Reactions, Lactones, Methodology, Ring contraction, Sesquiterpenes | Leave a Comment »

Ring Contraction of Taxol

Posted by naturalproductman on March 22, 2010

T. Narender and co-workers at the Central Drug Research Institute in India have recently reported in the Journal of Natural Products of all places, on a novel contraction of the six membered ring in taxol to a five membered ring using BF3 etherate.

ring contraction

JNP paper

Posted in C-C Bond Breaking, C-X Bond Breaking, Methodology, Ring contraction, Taxanes | Leave a Comment »

 
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