Sakurai reaction
{{Short description|Chemical reaction}}
{{Use dmy dates|date=December 2022}}
{{Reactionbox
|Name = Sakurai reaction
|Type = Addition reaction
|NamedAfter = Hideki Sakurai
Akira Hosomi
|Section3 = {{Reactionbox Identifiers
| OrganicChemistryNamed = hosomi-sakurai-reaction
| RSC_ontology_id = 0000443
}}
}}
The Sakurai reaction (also known as the Hosomi–Sakurai reaction) is the chemical reaction of carbon electrophiles (such as a ketone shown here) with allyltrimethylsilane catalyzed by strong Lewis acids.{{Cite journal|last=Hosomi|first=Akira|author1-link=Akira Hosomi|date=1988-05-01|title=Characteristics in the reactions of allylsilanes and their applications to versatile synthetic equivalents|journal=Accounts of Chemical Research|volume=21|issue=5|pages=200–206|doi=10.1021/ar00149a004|issn=0001-4842}}{{Citation|last1=Fleming|first1=Ian|title=The Electrophilic Substitution of Allylsilanes and Vinylsilanes|date=2004|work=Organic Reactions|pages=57–575|publisher=American Chemical Society|language=en|doi=10.1002/0471264180.or037.02|isbn= 9780471264187|last2=Dunoguès|first2=Jacques|last3=Smithers|first3=Roger}}{{Cite book|last=Fleming|first=Ian|title=2.2 – Allylsilanes, Allylstannanes and Related Systems|date=1991-01-01|chapter-url=http://www.sciencedirect.com/science/article/pii/B978008052349100041X|work=Comprehensive Organic Synthesis|pages=563–593|editor-last=Trost|editor-first=Barry M.|publisher=Pergamon|doi=10.1016/b978-0-08-052349-1.00041-x|isbn=9780080523491|editor2-last=Fleming|editor2-first=Ian|chapter=Allylsilanes, Allylstannanes and Related Systems}} The reaction achieves results similar to the addition of an allyl Grignard reagent to the carbonyl.
File:Sakurai Reaction Scheme.png
Strong Lewis acids such as titanium tetrachloride, boron trifluoride, tin tetrachloride, and AlCl(Et)2 are all effective in promoting the Sakurai reaction. The reaction involves electrophilic allyl shift via a beta-silyl carbocationic intermediate, the beta-silicon effect.{{Cite web|url=https://www.organic-chemistry.org/namedreactions/hosomi-sakurai-reaction.shtm|title=Hosomi-Sakurai Reaction|website=organic-chemistry.org|access-date=2019-09-01}}
Mechanism
Allylation of a carbonyl ketone (compound containing a ketone group and two different functional groups) has been shown. In the given reaction, the electrophilic compound (carbon with a ketone group) is treated with titanium tetrachloride, a strong Lewis acid and allyltrimethylsilane. According to the general principle, the Lewis acid first activates the electrophilic carbon in presence of allyltrimethylsilane which then undergoes nucleophilic attack from electrons on the allylic silane.{{Cite journal|last1=Yamasaki|first1=Shingo|last2=Fujii|first2= Kunihiko|last3=Wada|first3=Reiko|last4=Kanai|first4=Motomu|last5=Shibasaki|first5=Masakatsu|date= 2002-06-01|title=A General Catalytic Allylation Using Allyltrimethoxysilane|journal=Journal of the American Chemical Society|volume=124|issue=23|pages=6536–6537|doi=10.1021/ja0262582|pmid=12047165|issn=0002-7863}} The silicon plays the key role in stabilizing the carbocation of carbon at the β-position. The Sakurai reaction is also applicable for other functional groups such as enones, where conjugate addition is usually seen. In figure 2, the Sakurai reaction has been shown using a cinnamoyl ketone. This reaction follows the same mechanism as the previous reaction shown here.
As displayed in the scheme, the Sakurai reaction is proposed to give a secondary carbocation intermediate. Secondary carbocations are high in energy, however it is stabilized by the silicon substituent ("β-silicon effect", a form of silicon-hyperconjugation).
Literature of historic interest
- {{cite journal |last1=Sakurai |first1=Hideki |last2=Hosomi |first2=Akira |last3=Kumada |first3=Makoto |title=Addition of trichloromethyl radicals to alkenylsilanes |journal=The Journal of Organic Chemistry|date=1969 |volume=36 |issue=4 |pages=1764–1768 |doi=10.1021/jo01258a052}}
- {{Cite journal|last1=Hosomi|first1=Akíra|last2=Sakurai|first2=Hideki|title=Syntheses of γ,δ-unsaturated alcohols from allylsilanes and carbonyl compounds in the presence of titanium tetrachloride|journal=Tetrahedron Letters|year=1976 |volume=17|issue=16|pages=1295–1298|doi=10.1016/S0040-4039(00)78044-0|issn=0040-4039}}
- ({{Cite journal|last1=Hosomi|first1=Akira|last2=Endo|first2=Masahiko|last3=Sakurai|first3=Hideki|date=1976-09-05|title=Allylsilanes as synthetic intermediates. ii. syntheses of homoallyl ethers from allylsilanes and acetals promoted by titanium tetrachloride|journal=Chemistry Letters|volume=5|issue=9|pages=941–942|doi=10.1246/cl.1976.941|issn=0366-7022|doi-access=free}}
- {{Cite journal|last1=Hosomi|first1=Akira|last2=Sakurai|first2=Hideki|date=1977-03-01|title=Chemistry of organosilicon compounds. 99. Conjugate addition of allylsilanes to .alpha.,.beta.-enones. A New method of stereoselective introduction of the angular allyl group in fused cyclic .alpha.,.beta.-enones|journal=Journal of the American Chemical Society|volume=99|issue=5|pages=1673–1675|doi=10.1021/ja00447a080|issn=0002-7863}}
References
{{reflist}}
External links
- [https://www.organic-chemistry.org/namedreactions/hosomi-sakurai-reaction.shtm Hosomi-Sakurai reaction @ www.organic-chemistry.org]
- [https://web.archive.org/web/20121018161907/http://www.geocities.jp/ksntsuku70/ Akira Hosomi homepage]
Category:Nucleophilic addition reactions