By the Corey-Winter

Another theoretically interesting molecule, spiro[2.3]hex-4-ene (51), is obtained in 80% yield by the Corey-Winter elimination20 of ra-4,5-(thiocarbonyldioxy)spiro[2.3]hexane (50).21... 

Enantiomerically pure (.E)-l,l,3,3,6,6-hexamethyl-l-sila-4-cycloheptene 25, the smallest nonbridged (it)-cycloalk-ene which can be isolated in a pure form at room temperature, was synthesized by the Corey-Winter elimination of hexamethyl-l-sila-fra r-4,5-cycloheptanethiocarbonate 24 with l,3-dimethyl-2-phenyl-l,3,2-diazaphospholidine (Equation 7) C1997AGE159, 1999TA3483>. 

The absolute configuration of radiosumin, a novel potent trypsin inhibitory dipeptide, was determined by T. Shioiri and co-workers by carrying out the first enantioselective total synthesis of the natural product. The s-trans 1,3-diene in one of the key synthetic intermediates was installed by the Corey-Winter olefination using the Corey-Hopkins reagent (1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine). 

Crich, D. Pavlovich, A.B. Wink, D.J. Synthesis of fully-substituted enediynes by the Corey-Winter reaction. Synth. Commun. 1999, 29, 359-377. 

As expected, the yields of catenanes by this approach are low, which is why improved methods for the preparation of such compounds have been developed. The acyloins are often only intermediate products in a multistep synthesis. For example they can be further transformed into olefins by application of the Corey-Winter fragmentation. 

By application of the Corey-Winter reaction,vicinal diols 1 can be converted into olefins 3. The key step is the cleavage of cyclic thionocarbonates 2 (1,3-dioxolanyl-2-thiones) upon treatment with trivalent phosphorus compounds. The required cyclic thionocarbonate 2 can be prepared from a 1,2-diol 1 and thio-phosgene 4 in the presence of 4-dimethylaminopyridine (DMtVP) ... 

The Corey-Winter reaction provides a useful method for the preparation of olefins that are not accessible by other routes. For instance it may be used for the synthesis of sterically crowded targets, since the initial attack of phosphorus at the sulfur takes place quite distantly from sterically demanding groups that might be present in the substrate molecule. Moreover the required vicinal diols are easily accessible, e.g. by the carbon-carbon bond forming acyloin ester condensation followed by a reductive step. By such a route the twistene 10 has been synthesized ... 

Cyclic thionocarbonates (41) can be cleaved to olefins (the Corey-Winter reaction)274 by heating with trimethyl phosphite275 or other trivalent phosphorus compounds276 or by treatment with bis(l,5-cyclooctadiene)nickeI.277 The thionocarbonates can be prepared by treatment of 1,2-diols with thiophosgene and 4-dimethyIaminopyridine (DMAP) 278... 

The Corey-Winter olefin synthesis is based on the stereospecific loss of carbon dioxide or carbon disulfide from the carbenes formed by treatment with bivalent organophosphorus compounds of thionocarbonates or trithiocarbonates [218-220]. 

Alkenes from 1,2-diols (7, 385-386). An efficient synthesis of (S)-(—)-y-methoxymethyl-a, /J-butenolide (3) from (+)-5-0-methyl-D-ribonolactone (1) involves conversion to the cyclic orthoformate 2 followed by pyrolysis to give 3 in 66.5% overall yield.1 In this case, the Corey-Winter reaction and the Hanessian route (8,192) were... 

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 di-O-tosylates (prepared by action of tosyl chloride in pyridine) are reduced with zinc (Nal/Zn route e Tipson-Cohen reaction) [13]. Cyclic ortho-esters (prepared by reaction of the diol with ethyl orthoformate) are transformed into olefins by simple heating in the presence of acids (Eastwood reaction, route b) [14]. Cyclic thiocarbonates (obtained by reaction of a diol with thiophosgene or (V,(V -thiocarbonyl-di-imidazole) are reduced to olefin with trimethyl phosphite (Corey-Winter method, route c) [15]. Finally, reduction of vicinal di-xanthates with tri- -butyltin hydride according to the Barton procedure [16] affords olefins via a reductive elimination process route a). The Corey-Winter, Garegg, and Tipson-Cohen methods are most commonly applied for deoxygenation of sugar diols. 

The high temperatures and protracted reaction times required for the Corey-Winter reaction can lead to detrimental side reactions. Much lower reaction temperatures can be achieved by using 1,3-dimethyl-... 

The enantiospecific synthesis of naturally occurring cyclohexane epoxides such as (+)-crotepoxide and (+)-boesenoxide was accomplished by T.K.M. Shing et al. The key Intermediate 1,3-cyclohexadlene was prepared using the Corey-Winter protocol on a c/s-vicinal diol. The resulting diene was then converted to the natural product after several steps. 

Cyclic thionocarbonates (78) by heating with trimethyl phosphite yield (Z)-alkenes (84) (the Corey-Winter reaction). The starting thionocarbonates (78) may be prepared by condensation of thiophosgene with v/c-glycols (82) (X = 0) or v/c-thiols (82) (X = S) (Scheme 43). The Corey-Winter reaction may proceed via the carbenoid intermediate (83), which subsequently collapses to yield the (Z)-alkene... 

The Corey-Winter reaction is a valuable route for the synthesis of unsaturated sugars and complex cycloalkenes. Alkenes may also be obtained by pyrolysis of methyl xanthates... 

Double bonds can be created by a number of available stereospecific reactions (E2 elimination, pyrolytic elimination, e.g. Cope, Chugaev reactions), stereoselective Wittig and related reactions, reduction of triple bonds, by cisitrans isomerisation of existing double bonds either photochemically or by wet chemistry, e.g. the Corey-Winter procedure. [17]... 

There have been several modifications to the Corey-Winter reaction, the most significant of which was published by the Corey group in 1982.9 Corey and Hopkins reported that by using a diazaphospholidine in place of trimethylphosphite, thionocarbonates could be converted to the corresponding olefins at significantly lower temperatures. Thus, thionocarbonate 20 was prepared from diol 19 in 93% yield, and subsequent treatment of 20 with diazaphospholidine 21 afforded olefin 22 in 88% yield. Several complex examples were disclosed in which olefins were generated in 70-94% yield.9... 

The Corey-Winter reaction proceeds with complete stereospecificity by a syn elimination pathway, allowing the stereospecific synthesis of alkenes. Thus, anti-1,2-diphenylethane-1,2-diol was converted into cis -stilbene (2.45), whereas the corresponding syn-diol gave irans -stilbene. The strained fi-cyclooctene was prepared from the Z-isomer using this procedure (2.46). An alternative stereospecific route to alkenes proceeds from the diol with ethyl orthoformate or WA(-dimethylformanude dimethyl acetal, or by conversion of the diol to a 2-phenyl-1,3-dioxolane and treatment with an organolithium reagent to promote proton abstraction at C-2 and... 

Elimination of thionocarbonates is termed the Corey-Winter reaction (see Section 2.5). Attack by the phosphorus reagent on the sulfur atom is followed by fragmentation to give the alkene. See A. Krief, L. Provins and A. Froidbise, Tetrahedron Lett., 43 (2002),... 

Alkene Synthesis. The Corey-Winter alkene synthesis is an effective method for the deoxygenation of vicinal diols. The method involves formation of a l,3-dioxolane-2-thione [cyclic thionocarbonate (or thiocarbonate)] by treatment of a vicinal diol with TCDI. Decomposition of the thionocarbonate, usually with a phosphorus compound, affords the alkene (eq 1 ). The breakdown of the thionocarbonate occurs in a stereospecific sense details of investigations into the mechanism have been summarized. ... 

The method has found its niche in the chemistry of sugars. Their polyhydroxylated nature make them excellent substrates provided the by-standing hydroxyls are protected (eq 3). The 2 - and 3 -oxygens of nucleosides are readily are removed under the Corey-Winter conditions. ... 

Transformation of diols to the corresponding olefins by sequential treatment with l,r-thiocarbonyldiimidazole and trimethylphosphite. Also known as Corey-Winter reductive elimination, or Corey-Winter reductive olefmation. 

Corey and Winter converted 1,2-diol into a cyclic thionocarbonate 4.23 on heating with thiocarbonyldiimidazole (4.22) in toluene or xylene. Thionocarbonates 4.23 can also be prepared by the reaction of diol with n-butyllithium, followed by the reaction with carbon disulfide and methyl iodide. Desulfurization-decarboxylation is carried out by heating the cyclic thionocarbonate 4.23 with trimethylphosphite, and alkene is produced (Scheme 4.17). 

Diols are easily accessible from alkenes by the reaction with osmium tetroxide, and constitute another protection of the double bond since a variety of methods for the reformation of the alkenes from them is available. Among the important methods which proceed stereospecifically, the desulfurization of 2-thioxo-l,3-dioxolanes (e.g. 102, Corey-Winter reaction),the acid-catalyzed decomposition of... 

Corey-Winter olefin synthesis. Synthesis of olefins from 1,2-diols and thiocarbonyldiimidazole. Treatment of the intermediate cychc thionocarbo-nate with trimethylphosphite yields the olefin by els elimination. 

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. 

---