Phosphite Corey-Winter olefin synthesis

Corey-Winter olefin synthesis. The Corey-Winter olefin synthesis (1, 1233-1234) involves treatment of a thionocarbonale with trimethyl phosphite ... 

Corey-Winter olefin synthesis (I. I23.3-I234). Chong and Wiseman were able to demonstrate the transient existence of bicyclo[3.2.l]octenc-l (2, a bridgehead alkene which violates Bredt s rule) by application of the Corey-Winter olefin synthesis. Thus treatment of the thionocarbonatc (I) with triethyl phosphite at reflux (165°) fur 24 hr. in the presence of I,3-diphenyli obenzofurane (1, 342-343 2, 178-179) leads to the formation of two Diels-Alder adducts (3) and (4) derived from (2). 

The Corey-Winter olefin synthesis is a two-step transformation of a diol 1 to an olefin 3.1"3 A cyclic thionocarbonate 2 is prepared from the diol 1, and subsequent heating of 2 with phosphite affords olefin 3. 

Corey-Winter olefin synthesis (1, 1233-1234 2,439-441 3,315-316 4, 269-270, 541-542 5,34, 661). Vedejs and Wu converted thionocarbonates into olefins by alkylation with methyl iodide (90°, DME, sealed tube) followed by reduction (zinc dust—ethanol or magnesium amalgam—THF). This two-step procedure was used for preparation of the cyclobutene (2) in this case the reaction with triethyl phosphite was immeasurably slow. 

Phosphites can abstract the sulfur from the thione group to generate a car-bene. Trithiocarbonates are similarly desulfurized (110) and this reaction forms the basis of the Corey-Winter olefin synthesis (111). 

Olefin synthesis. Corey and Winter" devised a novel olefin synthesis from 1,2-diols utilizing in the first step the reaction with thiocarbonyldiimidazole (2), a reagent prepared from 2 moles of imidazole and 1 mole of thiophosgene. Corey postulated that treatment of the cyclic thionocarbonate (3) with a reagent which would abstract sulfur to form the curbenc (4) would effect cis elimination to the olefin and found that trimethyl phosphite effects this reaction cleanly and in high yield. [Pg.1350]

---