Deoxygenation of vicinal diols

B. Reactions in Which Neither Leaving Atom is Hydrogen 17-17 Deoxygenation of Vicinal Diols... 

A new synthesis of olefins by the reductive deoxygenation of vicinal diols using tungsten(iv) compounds, e.g. K2[WCl6], has been described. The process appears to be the reverse of the reaction of OsO with olefins and to involve transition state (90) since, in corresponding reactions, M0CI4 only forms... 

E. Block, Olefin Synthesis via Deoxygenation of Vicinal Diols, Org. React. 1984, 30, 457-566. 

E. Block, Olefin synthesis via deoxygenation of vicinal diols, Org. React. (N.Y.) 1984, 30, 457. M. M. Midland, Asymmetric reduction with organoborane reagents, Chem. Rev. 1989,89, 1553. H. C. Brown and P. V. Ramachandran, Asymmetric reduction with chiral organoboranes based... 

Sharpless, K. B., Flood, T. C. Direct deoxygenation of vicinal diols with tungsten(IV). New olefin synthesis. J. Chem. Soc., Chem. Common. 1972,370-371. 

Olefin Synthesis via Deoxygenation of Vicinal Diols Eric Block... 

Improved Catalytic Deoxygenation of Vicinal Diols and Application to Alditols... 

Judicious modification of the ligand environment in LReOs complexes allows successful catalytic deoxygenation of vicinal diols using PPha as terminal reductant. There is a steric bias toward diol units at the end of a linear chain (versus internal diols) and for erythro internal diols over threo. The potential for synthetic applications is discussed. 

Scheme 3. Catalytic deoxygenation of vicinal diols with Tp ReOs.

We have successfully demonstrated the principle of selective catalytic reductive deoxygenation of vicinal diols. The challenges inherent to this transformation have hindered development of carbohydrate-based organic feedstock chemistry. While there remain aspects of our chemistry that keep it a laboratory methodology, there is now a clear route to development. 

Alkenes. A simple procedure is reported for the reductive deoxygenation of vicinal diols to alkenes the stereospecificity is variable, and tetrasubstituted diols are most rapidly reduced. Typically, l,2-dimethylcyclododecane-l,2-diol in THF was treated with methyl-lithium followed by K2WCI6 hydrolysis gave 1,2-dimethylcyclododecene (58 %). 

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 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. 

As vicinal dibromides are usually made by bromination of alkenes, their utility for synthesis is limited, except for temporary masking of a double bond. Much more frequently it is desirable to convert a diol to an alkene, and several useful procedures have been developed. The reductive deoxygenation of diols via thiono carbonates was... 

Deoxygenation of vie-dials Secondary-tertiary (both cis and tram) vicinal diols are converted into alkenes directly by treatment with chlorotrimethylsilane and sodium iodide in CH3CN at room temperature (80-95% yield, seven examples). 

Saturated O-heterocycles as intermediates in synthesis of olefins by vicinal diol deoxygenation 84OR(30)457. 

The chemistry of )9-(thiocarbonyloxy)alkyl radicals stands in complete contrast to that of the (acyloxy)alkyl radicals, with elimination, while not the rule, being the norm [I]. The difference between the acyloxy and thiocarbonyloxy series is likely a consequence of the much weaker thiocarbonyl bond and the related higher stability of sulfur-centered radicals. The method has been developed in combination with the Barton deoxygenation method (Volume 1, Chapter 1.6) as a means of converting a vicinal diol, via the dixanthate, into an alkene (Scheme 33) [60-62]. Tributyltin hydride has been the reagent of choice for this reaction but it may also be conducted with the triethylsilane/benzoyl peroxide couple [63] and, doubtless, tris(trimethylsilyl)silane. 

Cleavage of Epoxides. Reaction of epoxides with 1 equiv of TMS-I gives the vicinal silyloxy iodide. With 2 equiv of TMS-I, however, epoxides are deoxygenated to afford the corresponding alkene (eq 4). However, allylic alcohols are efficiently prepared by reaction of the intermediate iodosilane with base. Furthermore, acyclic 2-ene-1,4-diols react with TMS-I to undergo dehydration, affording the corresponding diene. ... 

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