Home

About

Advanced Search

Browse by Discipline

Scientific Societies

E-print Alerts

Add E-prints

E-print Network
FAQHELPSITE MAPCONTACT US


  Advanced Search  

 
Radical-Anionic Cyclizations of Enediynes: Remarkable Effects of Benzannelation and Remote Substituents on
 

Summary: Radical-Anionic Cyclizations of Enediynes: Remarkable
Effects of Benzannelation and Remote Substituents on
Cyclorearomatization Reactions
Igor V. Alabugin* and Mariappan Manoharan
Contribution from the Department of Chemistry and Biochemistry, Florida State UniVersity,
Tallahassee, Florida 32306-4390
Received December 10, 2002; E-mail: alabugin@chem.fsu.edu
Abstract: The reasons for large changes in the energetics of C1-C5 and C1-C6 (Bergman) cyclizations
of enediynes upon one-electron reduction were studied by DFT and Coupled Cluster computations. Although
both of these radical-anionic cyclizations are significantly accelerated relative to their thermal counterparts,
the acceleration is especially large for benzannelated enediynes, whose reductive cyclizations are predicted
to proceed readily under ambient conditions. Unlike their thermal analogues, the radical-anionic reactions
can be efficiently controlled by remote substitution, and the effect of substituent electronegativity is opposite
of the effect on the thermal cycloaromatization reactions. For both radical-anionic cyclizations, large effects
of benzannelation and increased sensitivity to the properties of remote substituents result from crossing of
out-of-plane and in-plane MOs in the vicinity of transition states. This crossing leads to restoration of the
aromaticity decreased upon one-electron reduction of benzannelated enediynes. Increased interactions
between nonbonding orbitals as well as formation of new aromatic rings (five membered for the C1-C5
cyclization and six membered for C1-C6 cyclizations) are the other sources of increased exothermicity for
both radical-anionic cyclizations. The tradeoff between reduction potentials and cyclization efficiency as

  

Source: Alabugin, Igor - Department of Chemistry and Biochemistry, Florida State University

 

Collections: Chemistry; Biology and Medicine