Life-Long Focus on Four-Membered Rings

Seminar series
Organic Colloquium
Thu, Nov 8 4:00pm
Franz Hall 1178
Speaker Prof. Masahiro Murakami
Kyoto University
Department of Chemistry

Abstract: A four-membered ring is a unique structural motif endowed with strain energy.  Four-membered ring compounds have been posing various challenges for organic chemists to tackle.  How to make four-membered ring compounds starting from more easily available and less strained compounds, how to transform the strained structures into synthetically useful compounds, how to control the reativities peculiar to four-membered ring structures, etc.  My life-long work on the syntheses and reactions of four-membered ring compounds will be presented.

I started a study on four-membered ring compounds in 1994, when it was discovered that the  carbon–carbon bond of a cyclobutanone is cleaved by a rhodium(I) catalyst [Nature, 1994, 370, 540]. 

I also worked on the issue of torquselectivity of the 4 electrocyclic ring-opening reaction of cyclobutenes.  This concept was initially proposed by Professor K. Houk.  I found an interesting electron-accepting nature of the * orbital of a C–Si bond, which operated with 3-silylcyclobutene to favor inward rotation of the silyl group despite of arising steric congestion [Angew. Chem. Int. Ed., 2001, 40, 189].

The most striking behavior of four-membered rings was identified in a palladium-catalyzed reaction of benzocyclobutenone with silacyclobutane.  Two  bonds, one is a carbon–carbon bond and the other is a carbon–silicon bond, are cleaved to undergo exchange, achieving  bond metathesis [J. Am. Chem. Soc. 2017, 139, 12414]. 

On the other hand, the concept of substrate availability has led me to develop a new synthetic method of benzocyclobutenone starting from toluoyl chloride.  It would become a method of choice for preparation of benzocyclobutenone in a laboratory [Org. Lett. 2018, 20, 1224].