Glycals iodinated

Palladium catalyzed cross-coupling reactions of 1-substituted glycals have not only been limited to tributylstannyl derivatives. In fact, the versatility of this approach is significantly enhanced by the fact that C-l zinc-, indium-, or iodine-substituted glycals (easily accesible from glycals, see Scheme 7)... 

It was known from solution-based studies that an iodonium electrophile adds to the glycal linkage, in the presence of a sulfonamide, in a transdiaxial fashion.24 This results in formation of a 1 -a-sulfonamido-2-p-iodo product. Furthermore, displacement of iodine can be induced by nucleophilic attack of a thiolate nucleophile... 

In addition, iodine snccessfnlly catalyzed the electrophilic snbstitntion reaction of indoles with aldehydes and ketones to bis(indonyl)methanes [225], the deprotection of aromatic acetates [226], esterifications [227], transesterifications [227], the chemoselective thioacetalization of carbon functions [228], the addition of mercaptans to a,P-nnsatnrated carboxylic acids [229], the imino-Diels-Alder reaction [230], the synthesis of iV-Boc protected amines [231], the preparation of alkynyl sngars from D-glycals [232], the preparation of methyl bisnlfate [233], and the synthesis of P-acetamido ketones from aromatic aldehydes, enolizable ketones or ketoesters and acetonitrile [234],... 

Bis(5> m-collidine)iodine(I) tetrafluoroborate in DMSO has been found to be a convenient reagent for the conversion of alkanes to a-iodocarbonyl compounds. When dihydrofuran (305a) and dihydropyran (305b) are the substrates, this reaction affords the corresponding a-iodolactones 306 (Scheme 77). This method converts certain glycals such as 307 to their corresponding a-iodo-a,/3-unsaturated lactones 309, presumably because of elimination of a molecule of acetic acid from the initially formed lactone 308 (86S727) (Scheme 78). 

Phenylselenyl chloride adds to the double bond of the glycal 26 to give a phenyl-selenoxonium ion which is tra/w-opened by an approaching nucleophile to the glycoside 27. Other electrophiles have also been used likep-toluenesulfonic acid, bromine, or iodine. Acid conditions, however, may cause destruction of labile 2-deoxy sugar products and the value of such reagents will be diminished by this evident disadvantage. 

A. Kirschning, G. Drager, and J. Harders, Regioselective oxidation of glycals with hypervalent iodine reagents, Synlett, (1993) 289-290. 

The mechanism of glycal addition was further examined by Horton and coworkers,86 who have used this method to form (7S,9S)-4-demethoxy-7-0-(2,6-dideoxy-2-iodo-a-L-mannopyranosyl)-adriamycinone87 and -daunomycinone,88 which are iodinated analogs of natural antitumor compounds. The nature of the solvent was found to be critical. In particular, they were able to generalize that in non-coordinating polar solvents, where no possibility for interaction with iodine exists—that is, no lone-pair interactions—the formation of the iodonium intermediate was irreversible, and the resultant stereochemistry reflects the electronic... 

A number of 2-deoxy-2-iodopyranosyl isothiocyanates 12 have been prepared in good yields and high diastereoselectivity by treatment of glycals 11 with an iodine/potassium thiocyanate/ silica gel system189 204-206. 

The synthesis of the nucleoside 20 was eventually performed by addition of a silylated base to the double bond of the furanoid glycal 19 after activation with iodine. The reaction proceeds with total stereoselectivity and the configuration of the newly introduced stereogenic centers was assigned by H NMR214. 

Addition of iodine azide to glycals gives mostly the l,2-trows-2-deoxy-2-iodoglycosyl azides [75]. In view of the hazardous nature of iodine azide, two mild methods were devel-... 

To install the appropriate functionality at C2, solution phase chemistry has relied on a trans-diaxial addition of an iodonium electrophile in the presence of an amine to form an iodosulfonamide. Displacement of iodine proceeds presumably through an aziridine intermediate and may be induced by a thiolate nucleophile to fashion thioethyl 2-amidoglycosyl donors [38]. Successful transfer of this method to the solid support allowed polymer-bound glycals to be converted into thioethyl gly-cosyl donors. These donors were in turn coupled with a variety of glycosyl acceptors, including glycals [39]. 

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