Bergman rearrangements

It is noteworthy that Jones and Darby, who pioneered the enediyne rearrangement, now known as the Bergman rearrangement, and Nicolaou, who achieved the first total synthesis of the enediyne antibiotic calicheamicin 7 / were under the joint supervision of Profs. Franz Sondheimer and Peter Garratt. It might seem that all researchers in the enediyne field have been influenced by Sondheimer and Garratt. 

Detailed thermochemical data for the Bergman rearrangement were determined by Roth et al. from gas-phase NO trapping experiments. The activation barrier for ring opening of 28 to enediyne (Z)-16 was reported as 19.8 kcal/mol, the enthalpy of formation of (Z)-16 293 = 129.5 kcal/mol) is lower than that of p-benzyne... 

The aza-Bergman rearrangement of C,A-dialkynylimines to p-alkynyl acrylonitriles has also been studied intensively. In 1997, David and Kerwin investigated the thermochemistry of (Z)-118 in solution and observed rearrangement to (Z)-119... 

Photoexciting 1,4-dibromobenzene in a molecular beam with 307-nm pump pulse photons leads to sequential loss of both bromine atoms within 100 fs the excited dibromide has a lifetime of 50 fs and the monobromide of 80 fs. The p-benzyne generated decays relatively slowly, showing a lifetime of 400 ps. It presumably leads to (Z)-3-hexene-l,5-diyne through a valence isomerization of the sort associated with the Bergman rearrangement. 

Feng, L., Kumar, D., Kerwin, S. M. /tn Extremely Facile /tza-Bergman Rearrangement of Sterically Unencumbered Acyclic 3-Aza-3-ene-... 

Conformational changes are observed also in the 1,2-aryldiyne system 117 bearing two phosphine groups at its extremities synthesized by Warner et al. " in this case the complexation to ions such as Pd and Pt " " activates the Bergman rearrangement, while Hg stabilizes the aryldiyne moiety (Scheme 19.32). The author proposes that not only conformational changes, but also electronic effects, may contribute to the reactivity. Electronic effects are observed in a third example by Wang and Finn ... 

Scheme 7-6 Tandem Claisen/Bergman rearrangement strategy for stereocontrolled tetrahydionaph-thalene synthesis (Magriods and Kim).

Both vinyl- and alkynyl-9-BBN derivatives are effective dieno-philes in Diels-Alder cycloadditions, leading to boron-functionalized cyclohexenes in a selective manner (eqs 37 and 38). Silylated allenylboranes add selectively as allylboranes to aldehydes, a reaction which has been effectively used to prepare the steroid nucleus through a Hudrlik elimination followed by a Bergman rearrangement (eq 39). ... 

Scheme 3.1 Structure of the C-1027 chromophore 3.407 and its Masamune-Bergman rearrangement to 3.411.

Feng, L., Zhang, A. and Kerwin, S.M. (2006) Enediynes from aza-enediynes C,N-dialkynyl imines undergo both aza-Bergman rearrangement and conversion to enediynes and fumaronitriles. Organic Letters, 8(10), 1983-1986. 

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