TheCorey–Winter olefin synthesis (also known asCorey–Winter–Eastwood olefination) is a series ofchemical reactions for converting 1,2-diols intoolefins.[1][2][3][4] It is named for the American chemist and NobelistElias James Corey and the American-Estonian chemistRoland Arthur Edwin Winter.[5]
Often,thiocarbonyldiimidazole is used instead ofthiophosgene as shown above, since thiophosgene has a similar toxicity profile as phosgene, whereas thiocarbonyldiimidazole is a much safer alternative.
Thereaction mechanism involves the formation of a cyclic thiocarbonate from the diol andthiophosgene. The second step involves treatment withtrimethyl phosphite, which attacks thesulfur atom, producing S=P(OMe)3 (driven by the formation of a strong P=Sdouble bond) and leaving acarbene.[6] This carbene collapses with loss ofcarbon dioxide to give the olefin.
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 astereospecific reaction:[1] atrans-diol gives atrans-alkene, while acis-diol gives acis-alkene as the product. For instance,cis- andtrans-1,2-cyclodecanediol gives the respectivecis- andtrans-cyclodecene.