2006 Fiscal Year Final Research Report Summary
Development of New Synthetic Reactions Using Organosilicon Compounds
| Project/Area Number |
14078205
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas
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| Allocation Type | Single-year Grants |
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| Review Section |
Science and Engineering
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| Research Institution | University of Tsukuba |
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Principal Investigator |
HOSOMI Akira University of Tsukuba, Department of Chemistry, Professor Emeritus, 名誉教授 (00004440)
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| Project Period (FY) |
2002 – 2005
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| Keywords | Organosilicon Reagents / Indium Catalyst / Reduction / Carbon-Carbon Bond Formation / Silyl Enolates / Aldol Reaction |
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| Research Abstract |
Most of organosilicon reagents have a trimethylsilyl (TMS) group or a more bulky triorganosilyl group. Synthetic utility of silicon reagents bearing a less bulky silyl group has remained unexplored. We have found that dimethylsilyl (DMS)-protected nucleophiles are more reactive than TMS-protected nucleophiles. For example, in the presence of CaCl_2, ketone DMS enolates added smoothly to aldehydes at 30℃ in DMF to give aldols in high yield. Under the same conditions, the corresponding TMS enolates did not react with aldehydes at all. In the reaction of DMS enolates, CaCl_2 would serve as Lewis base to activate the enolates by nucleophilic attack of the silicon by the chloride ion. DMS enolates are useful for the Mannich-type reaction of N-tosylimines and the Michael reaction of a-enones. Similarly, α-DMS-esters are more reactive than the corresponding TMS-based reagents. In the presence of metal chlorides (LiCl, MgCl_2, etc.), aldehydes and ketones underwent efficient aldol reactions of α-DMS-esters.
In general, hydrosilanes do not react spontaneously with carbon electrophiles ; however, their reducing ability can be drawn by activation of the substrates or themselves. A proper choice of activator enables fine control of the reduction process. We have found that PhSiH_3 reacts with haloalkanes in the presence of In(OAc_3) to form the dehalogenated alkanes. This reduction would involve a radical chain mediated by indium hydride species. The PhSiH_3-In(OAc_3) system is applicable to intermolecular radical addition of haloalkanes to electron-deficient alkenes. Additionally, it is valuable also for reductive aldol reaction of a-enones with aldehydes. In this case, a plausible mechanism consists of ionic 1,4-reduction of a-enones with indium hydride species and aldol reaction of the resultant indium enolates.
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