Reactions Bergman cycloaromatization

To make the Bergman cyclization synthetically more appealing, the reaction temperature had to be lowered 

Porphyrin chromophores have received much attention, particularly as photoelectric devices and molecular wires. Efficient re-electronic communication between porphyrin macrocycles is pivotal in various complex functions. K.M. Smith et al. showed that neighboring acetylenic units on porphyrins provide a means for the efficient construction of aromatic superstructures triggered by the Bergman cyclization reaction conditions and give rise to novel [n]phenacenoporphyrins, which belong to a new class of highly re-extended porphyrins.  

Research by S.J. Danishefsky et al. has shown that calicheamicin/esperamicin antibiotics containing an allylic trisulfide trigger can undergo a mild Bergman cyclization when treated with benzyl mercaptan.  

When the enediyne substrate has functional groups that can trap the initially formed Bergman diradical, the rapid construction of complex fused ring systems becomes feasible. J.E. Anthony and co-workers prepared an acenaphthene derivative as well as a substituted perylene using this concept.  

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Figure 9.9 Bergman cycloaromatization reactions for ltex-3-ett-l,5-diyne and its perfluorinated congener, as well as a photochemical reaction scheme for generating the perfluorinated diradical from an iodinated precursor. What spectral features would be expected to be most diagnostic of the different intermediates What levels of theory would be appropriate for predicting these spectral signatures (Note that equilibrium arrows of unequal length indicate which species predominates at equilibrium.)...

Irradiation of a series of 4,5-bis(alkyn-l-yl)imidazoles (R = Me, Bu, Ph) (450 W low-pressure Hg) induced Bergman cycloaromatization reactions providing benzimidazole derivatives. The cyclized product (R = Ph) was obtained in highest yields (26-64%) with the best result obtained in THF (Scheme 121) <2005TL1373>. 

Bergman cycloaromatization reaction Thermal or photochemical cycloaromatization of enediynes to form substituted benzene rings. 56... 

Related reactiens Bergman cycloaromatization reaction, Danheiser benzannulation ... 

Turro, N.J. Evenzahav, A. Nicolaou, K.C. Photochemical analogue of the Bergman cycloaromatization reaction. Tetrahedron Lett. 1994, 35, 8089-8092. 

Draw mechanism arrows to show electron movements in the Bergman cycloaromatization reaction that leads to the dimdical believed responsible for the DNA-deaving action of the antitumor agent calicheamicin (see Why Do These Topics Matter after Section 10.12). 

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