2000 Fiscal Year Final Research Report Summary
Selective Generation of Carbocations and Construction of Fused Ring Systems by Using α-Cation-Stabilizing Effect of Fluorine
| Project/Area Number |
11650899
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Synthetic chemistry
|
|---|
| Research Institution | The University of Tokyo |
|---|
Principal Investigator |
ICHIKAWA Junji The University of Tokyo ; Graduate School of Science ; Associate Professor, 大学院・理学系研究科, 助教授 (70184611)
|
|---|
| Project Period (FY) |
1999 – 2000
|
| Keywords | difluoroolefin / α-fluorocarbocation / fused cyclic system / tandem cyclization / protic acid / Friedel-Crafts cyclization / bicyclic ketone / helicene |
|---|
| Research Abstract |
Fluorine possesses (i) α-cation-stabilizing effect and (ii) leaving-group ability as fluoride ion (F^-). Using these properties, we have recently developed fluorine-directed Nazarov cyclizations via α-fluorocarbocations generated from 2,2-difluorovinyl vinyl ketones. Our interest on fluorine-containing carbocations prompted us to investigate their generation from simple 1,1-difluoroolefins without a carbonyl group, which would allow ring constructions by intramolecular trapping of the cations with unsaturated groups. Furthermore, to expand the scope of α-fluorocarbocation chemistry, we also explored the generation of fluoroallyl cations from conjugated 1,1-difluorodienes by regioselective protonation of the non-fluorinated double bond. Thus, we have accomplished intramolecular Friedel-Crafts cyclizations of 1,1-difluoro-1-alkenes and 1,1-difluoro-1,3-alkadienes bearing one or two aryl groups. These reactions efficiently provide a variety of fused polycyclic compounds.
Treatment of 1,1-difluoro-1-alkenes or 1,1-difluoro-1,3-alkadienes bearing an aryl group with FSO_3H SbF_5 or p-toluenesulfonic acid, respectively, promotes intramolecular Friedel-Crafts reactions in (CF_3)_2CHOH (HFIP). The cyclizations proceed via terminal α-fluorocarbocations generated by regioselective protonation of the double bond. Bicyclic ketones are eventually obtained after spontaneous hydrolysis of the C-F bonds.
In the case of difluoroolefins bearing two aryl groups, tandem cyclizations successfully occur to afford fused polycyclic compounds, whose dehydrogenation with palladium on activated carbon leads to [4]helicenes in high yields.
|
Research Products
(2 results)
