Corey–Winter olefin synthesis
The Corey–Winter olefin synthesis (also known as Corey–Winter–Eastwood olefination) is a series of chemical reactions for converting 1,2-diols into olefins.{{cite journal |last1=Corey |first1=E. J. |last2=Winter |first2=R. A. E. |author1-link=Elias James Corey |title=A New, Stereospecific Olefin Synthesis from 1,2-Diols |journal=J. Am. Chem. Soc. |date=1963 |volume=85 |issue=17 |pages=2677–2678 |doi=10.1021/ja00900a043|bibcode=1963JAChS..85.2677C }}{{cite journal |last1=Corey |first1=E. J. |last2=Carey |first2=F. A. |last3=Winter |first3=R. A. E. |title=Stereospecific Syntheses of Olefins from 1,2-Thionocarbonates and 1,2-Trithiocarbonates. trans-Cycloheptene |journal=J. Am. Chem. Soc. |date=1965 |volume=87 |issue=4 |pages=934–935 |doi=10.1021/ja01082a057|bibcode=1965JAChS..87..934C }}{{cite journal |last1=Corey |first1=E. J. |last2=Hopkins |first2=J. |title=A mild procedure for the conversion of 1,2-diols to olefins |journal=Tetrahedron Lett. |date=1982 |volume=23 |issue=19 |pages=1979–1982 |doi=10.1016/S0040-4039(00)87238-X}}{{cite journal |last1=Crank |first1=G. |last2=Eastwood |first2=F. W. |title=Derivatives of orthoacids. II. The preparation of olefins from 1,2-diols |journal=Australian Journal of Chemistry |date=1964 |volume=17 |issue=12 |pages=1392–1398 |doi=10.1071/CH9641392}} It is named for the American chemist and Nobelist Elias James Corey and the American-Estonian chemist Roland Arthur Edwin Winter.Block, E. Org. React. 1984, 30, 457. {{doi|10.1002/0471264180.or030.02}}
File:Corey-Winter olefination overview.svg
Often, thiocarbonyldiimidazole is used instead of thiophosgene as shown above, since thiophosgene has a similar toxicity profile as phosgene, whereas thiocarbonyldiimidazole is a much safer alternative.
Mechanism
The reaction mechanism involves the formation of a cyclic thiocarbonate from the diol and thiophosgene. The second step involves treatment with trimethyl phosphite, which attacks the sulfur atom, producing S=P(OMe)3 (driven by the formation of a strong P=S double bond) and leaving a carbene.Horton, D.; Tindall, Jr., C. G. J. Org. Chem. 1970, 35(10), 3558-3559. ({{doi|10.1021/jo00835a082}}) This carbene collapses with loss of carbon dioxide to give the olefin.
File:Corey-Winter olefination mechanism v1.svg
An alternative mechanism does not involve a free carbene intermediate, but rather involves attack of the carbanion by a second molecule of trimethylphosphite with concomitant cleavage of the sulfur-carbon bond. The phosphorus stabilized carbanion then undergoes an elimination to give the alkene, along with an acyl phosphite, which then decarboxylates.
The Corey-Winter olefination is a stereospecific reaction: a trans-diol gives a trans-alkene, while a cis-diol gives a cis-alkene as the product. For instance, cis- and trans-1,2-cyclodecanediol gives the respective cis- and trans-cyclodecene.
References
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{{Alkenes}}
{{Organic reactions}}
Category:Olefination reactions
Category:Elimination reactions
Category:Organic redox reactions
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