Corey-Winter reaction

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 ... 

Iodotrimethylsilane formed in situ from the reaction of chlorotrimethylsilane and sodium iodide, also effects the conversion of 2-ene-l,4-diols to 1,3-dienes (equation 16)46. Allylic thionocarbonates on heating with triphenylphosphite undergo deoxygenation (Corey-Winter reaction) to generate olefins47. This procedure has been used for making hexatrienes (equation 17)47b. 

Other reactions that may be used in a similar way are the Corey Winter reaction that converts 1,2-diols to alkenes270 other eliminations of known stereochemical course in suitable cases, fragmentations271. 

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... 

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... 

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... 

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-... 

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... 

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

However, evidence opposing the intermediacy of a carbene species in the Corey-Winter olefin synthesis also exists.3 Thermal decomposition of hydrazone salt 14, which is proposed to proceed via carbene 12, leads to a mixture of products 13, 15, and 16.7 Thus, an alternative mechanism has been proposed for the Corey-Winter reaction that invokes a phosphorus ylide. In this mechanistic scenario, initial reaction of thionocarbonate 10 with trimethylphosphite affords zwitterion 11. Cyclization generates... 

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 has found use in complex natural product synthesis. In one example, treatment of thionocarbonate 26 with diazaphospholidine 21 afforded diene 27 in 82% yield. This diene was ultimately used in a total synthesis of (-)-taxol.14... 

Overman and co-workers used the Corey-Winter reaction in total syntheses of two complex alkaloids. Treatment of thionocarbonate 28 with trimethylphosphite gave didehydrostemofoline 29 in 66% yield. Under the same conditions, isodidehydrostemo-foline 31 was obtained from thionocarbonate 30 in 64% yield.15... 

The Corey-Winter reaction has also been used in a formal synthesis of the AIDS drug (-)-abacavir (35).16 Thionocarbonate 33 was prepared from diol 32 in 78% yield. Then, treatment of 33 with phospholidine 21 afforded olefin 34 in 65% yield. The preparation of 34 constitutes a formal synthesis of (-)-abacavir (35). 

Note The modified Corey-Winter reaction, using 21, can also be run without solvent.16... 

This variation of the Corey-Winter reaction is not stereoselective thus the thionocarbonates of either cis- or fra/ji-cyclooctane-1,2-diol give only cis-cyclooctene. 

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