Thermal Bergman

Lastly, 2,4-quinazolinedione derivatives 917 have been prepared by thermal Bergman cycloaromatization of diethynylluracils 916 in 1,4-cyclohexadiene at 130 °C, although the yields were quite low <2000TL8741>. 

Rawat, D. S., Zaleski, J. M. Geometric and electronic control of thermal Bergman cyclization. Synlett 200i, 393-421. 

Choy, N. Blanco, B. Wen, J. Krishnan, A. Russell, K.C. Photochemical and thermal Bergman cyclization of a pyrimidine enediynol and enediynone. Organic Lett. 2000, 2, 3761-3764. 

Electronic Structure Contributions to Thermal Bergman CycUzation / 445 Photochemical Bergman CycUzation of Metalloenediynes / 449 Porphyrin—Enediyne Conjugates / 453... 

Electronic Structure Contributions to Thermal Bergman Cyclization... 

It was found that cyclization of benzannulated enediynes can be initiated by irradiation to give the same products as were obtained by thermal Bergman cyclization [238]. Photo-Bergman cyclization, which is also related to the chemistry of benzyne, has not been so extensively investigated. Terminal acyclic enediynes capable of cycloaromatization by thermal C -C route do not undergo photochemical initiation. However, introduction of one or two phenyl substituents in the acetylenic branches facilitates the C -C photocyclization of acyclic enediynes, but any increase in steric hindrance raises the activation barrier and the photochemical yield is significantly lower than in the case of their cyclic... 

A search for compounds capable of cycloaromatization under mild conditions was investigated by the synthesis of some enediynes by photochemical methods such as laser or other photosensitizers [240-249]. The enediynes 3.471 and 3.473 were synthesized by decarbonylation of 2,3-benzobicycloundec-l(10)en-4-yn-ll-one 3.470 [242] or the analogous quinone [243] that are sufficiently thermally stable to not decompose at 84°C for 7 days. The subsequent thermal Bergman cycloaromatization of the enediyne intermediates occurred at 40°C for 88 hours (Scheme 3.15) [242, 243]. 

Benites, P.J., Rawat, D.S. and Zaleski, J.M. (2000) Metalloenediynes ligand field control of thermal Bergman cyclization reactions. Journal of the American Chemical Society, 122(30), 7208-7217. 

---