Tipson-Cohen elimination

Synthesis of 2-deoxy-3-demethyoxyfortimicin A (390) has been described by Tadanier and Hallas [224]. This compound was prepared from the methanesulfonyl derivative 388 by application of the Tipson-Cohen elimination protocol to give the... 

Methods for preparation of mdo-glycals include that of Baptistella et al. [72], who used microwave irradiation to obtain mdo-glycals from gluco- and galacto-di-O-mesyl or di-O-tosyl derivatives, by means of Tipson-Cohen elimination reactions [73] (Scheme 12.39). 

Dramatic rate increases for Tipson-Cohen eliminations applied to vicinal dimesylate or ditosylate sugar derivatives to produce 2,3- and 3,4-unsaturated hexose compounds have been brought about by the use of microwave fields. ... 

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 generation of an alkene by the reaction of a v/c-disulfonate ester with iodide (the Tipson-Cohen reaction) has been known since 1943 and in some cases it has proved useful where other methods have failed, as in the preparation of the spirocyclic triene (54 Scheme 22). The mechanism probably involves an initial nucleophilic displacement to give an iodohydrin sulfonate, which then undergoes iodide-induced elimination to the alkene. Methanesulfonates can be used as well as arenesulfonates. 

Simple elimination did not occur as in the pyranoid series (see p. 232) when 2,3-frans-sulfonic esters were treated with the Tipson-Cohen reagent (sodium iodide and zinc in N,N-dimethylformamide) instead, 2,5-anhydro-3,4-di-0-p-tolylsulfonyl-D-xylose diisobutyl dithioacetal underwent a double elimination72 but see Ref. 76a. An alternative means of preparing 2,5-dihydrofuran derivatives that has its analogy in the pyranoid series (see p. 233) is, however, the treatment of appropriate aziridines with sodium nitrite in acetic acid, and, by this means, compound 41 [R = CH(S-isoBu)2, R = H] has been prepared in high yield.77... 

Mild eliminations of uic-diols to olefins, related to the Corey-Winter and Tipson-Cohen procedures, are outlined in Scheme These methods are... 

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