Bergman cyclization

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Masamune-Bergman cyclization
Named after Satoru Masamune

Robert George Bergman

Reaction type Ring forming reaction
Identifiers
Organic Chemistry Portal bergman-cyclization
RSC ontology ID RXNO:0000240

The Masamune-Bergman cyclization or Masamune-Bergman reaction or Masamune-Bergman cycloaromatization is an organic reaction and more specifically a rearrangement reaction taking place when an enediyne is heated in presence of a suitable hydrogen donor (Scheme 1).[1][2] It is the most famous and well-studied member of the general class of cycloaromatization reactions.[3] It is named for Japanese-American chemist Satoru Masamune (b. 1928) and American chemist Robert G. Bergman (b. 1942). The reaction product is a derivative of benzene.

Scheme 1. Bergman cyclization
Scheme 1. Bergman cyclization

The reaction proceeds by a thermal reaction or

1,4-dichlorobenzene and with methanol the reaction product is benzyl alcohol
.

When the enyne moiety is incorporated into a 10-membered hydrocarbon ring (e.g. cyclodeca-3-ene-1,5-diyne in scheme 2) the reaction, taking advantage of increased ring strain in the reactant, is possible at the much lower temperature of 37 °C.

Scheme 2. Bergman reaction of cyclodeca-3-ene-1,5-diyne
Scheme 2. Bergman reaction of cyclodeca-3-ene-1,5-diyne

Naturally occurring compounds such as

mylotarg.[5]

A

biradical mechanism is also proposed for the formation of certain biomolecules found in marine sporolides that have a chlorobenzene unit as part of their structure. In this mechanism a halide salt provides the halogen. A model reaction with the enediyene cyclodeca-1,5-diyn-3-ene, lithium bromide as halogen source and acetic acid as hydrogen source in DMSO at 37 °C supports the theory:[6][7]

Bergman cyclization with capture by lithium bromide
Bergman cyclization with capture by lithium bromide

The reaction is found to be

anion intermediate B. The anion is a powerful base, stripping protons even from DMSO to final product. The dibromide or dihydrogen product (tetralin
) never form.

Reversible Bergman cyclization of diyne induced by an AFM tip: model (top) and false-color AFM images (bottom)

In 2015 IBM scientists demonstrated that a reversible Masamune-Bergman cyclisation of diyne can be induced by a tip of an

atomic force microscope (AFM). They also recorded images of individual diyne molecules during this process.[8] When learning about this direct experimental demonstration Bergman commented, "When we first reported this reaction I had no idea that it would be biologically relevant, or that the reaction could someday be visualized at the molecular level.[9]

References

  1. doi:10.1039/C29710001516
    .
  2. doi:10.1021/ja00757a071
    .
  3. PMID 23600723
    .
  4. doi:10.1021/ar00008a003
    .
  5. doi:10.3998/ark.5550190.0007.719
    .
  6. PMID 17378569
    .
  7. ^ Borman, Stu (April 2, 2007). "New Route For Halide Addition". Chemical & Engineering News. Retrieved December 30, 2021.
  8. S2CID 21611919
    .
  9. ^ Sciacca, Chris (25 January 2016). "30 Years of Atomic Force Microscopy: IBM Scientists Trigger and Observe Reactions in an Individual Molecule". IBM Research News. IBM. Retrieved 25 January 2016.

External links

Wikimedia Commons has media related to Bergman cyclization.
  • Bergman Cycloaromatization Powerpoint Whitney M. Erwin 2002
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