Ring size matters

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

JOC paper

Transannular Claisen rearrangement

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.

OBC paper

Bi(OTf)3 mediated rearrangement

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.

OBC paper

Vinylogous Amides via Eschenmoser episulfide contractions

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

 

JOC paper

Ring Contraction via Iodination

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.

 

Chem Comm paper

6 to 5 Ring Contraction

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.

JACS paper

Ring Contraction for Spirocyclic Centers

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.

Chemistry A European Journal paper

A Ring Contraction Approach for Taiwaniaquinone

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.

Chemistry – a European Journal paper

Bakkenolide Synthesis

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.

JOC paper

Ring Contraction of Taxol

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.

JNP paper