1995 Fiscal Year Final Research Report Summary
Novel-Generation of Active Intermediates by Rearrangement of Main-Group Metals and Its Application to Heterocyclic Design
| Project/Area Number |
06453138
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Synthetic chemistry
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| Research Institution | Osaka University |
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Principal Investigator |
KOMATSU Mitsuo Osaka Univ., Faculty of Engineering, Professor, 工学部, 教授 (60029197)
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| Co-Investigator(Kenkyū-buntansha) |
ITOH Shinobu Osaka Univ., Faculty of Engineering, Associate Professor, 工学部, 助教授 (30184659)
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| Project Period (FY) |
1994 – 1995
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| Keywords | main-group metals / intramolecular migration / 1,3-dipoles / molecular design / cycloaddition / heterocyclic compounds / azomethine ylides |
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| Research Abstract |
In this project, novel methodology for generation of 1,3-dipolar active intermediates by rearrangement of main-group metals, such as silicon and stannane, has been developed and applied to heterocyclic design. One of the features of the methodology is that the intermediates can be generated under completely neutral conditions without any additive such as bases and/or demetallation agents.
Thermal rearrangement of alpha-silylimines to N-silylaziridines occurred via N-silylated azomethine ylides stereoselectively, while stannyl and germyl analogs did not isomerize to aziridines. On the other hand, the 1,3-dipolar intermediates were successfully generated from all the imines upon heating via 1,2-metal shift onto the imino nitrogen and they cycloadded to various dipolarophiles to give heterocyclic compounds with high stereoselectivity. These stereoselectivities are well explained by semi-empirical MO calculations. The order of the ease of migration of the metals was Sn>Si>Ge in contrast to that of their Lewis acidity. The greater migratrory ability of stannane enabled application of the methodology to generation of wider range of azomethine ylides.
Furthermore, 1,4-shift of the silyl group of alpha-silylamides onto the oxygen atom gave rise to azomethine ylides having an alpha-siloxy group. The in situ generated ylides were sffectively utilized for synthesis of heterocycles by cycloaddition with a variety of dipolarophiles.
Another new method for generation of azomethine ylides by fluorosilylation of azaallyl anions has been devised to lower the reaction temperature of the above thermal methods. Thus azaallyl anions generated from alpha-silylimines were treated with a difluorosilane to give N-fluorosilylazomethine ylides, which reacted with various dipolarophiles to afford nitrogen-containing heterocycles even at room temperature.
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