Cohen-Tipson reaction

In addition to these physical studies at the Bureau, Tipson was able to return to his synthetic interests, both alone and in collaboration with other staff members. He was especially pleased to prepare D-talose in crystalline form, an accomplishment that had eluded Emil Fischer. Pursuing his longstanding interest in the reaction of sulfonic esters with iodide and following an earlier observation that the tetratosyl ester of erythritol is converted into butadiene by the action of sodium iodide and zinc, he demonstrated (with A. Cohen) that nonterminal unsaturation may be conveniently introduced into alditol derivatives by reaction of contiguous secondary sulfonates with sodium iodide and zinc dust in boiling A.A-dimethylformamide. This Tipson-Cohen reaction subsequently proved of great utility in other hands for the conversion of more complex carbohydrate structures into vicinal dideoxy derivatives. 

Tipson-Cohen reaction, 30, 2 Tosylhydrazones, 23, 3 39, 1 Tosyhnethyl isocyanide (TosMIC), 57, 3 Transmetallation reactions, 58, 2 Tricar bonyl(r -arene)chromium complexes, 67, 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 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. 

During Tipson-Cohen reaction of ditosylate (16) (Nal/Zn/DMF) a minor by-product (13%) was isolated and identified as the 3-C-aryl derivative (17). The mixed sulfonates (18) and (19) were prepared and subjected to the same conditions to give, as well as the expected alkene (20), the by-products (21) and (17) respectively. A C-3 carbanionic intermediate was postulated which attacked the aromatic ring of the C-2 sulfonate expelling S02. Syntheses from D-glucose of a triquinane and of an intermediate in the synthesis of the ansa chain of... 

The preparation of methyl 4,6-0-benzylidene-2,3-dideoxy-j8-D-e/ > //[ro-hex-2-enopyranoside from the 2,3-disulphonates (84) using the Tipson-Cohen reaction has been noted in Chapter 6. ... 

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). 

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