Iodonium dicollidine perchlorate

TV-Bromosuccinirnide (NBS) and NIS are the most widely used electrophiles to activate -pentenyl glycosides. Catalytic amounts of acids such as TfOH or trieth-ylsilyl triflate (TESOTf) are introduced to speed up the generation of bromonium or iodonium ions [43], The stereochemical outcome depends, as usual, on whether a participating group exists at C2. An alternative promoter is iodonium dicollidine perchlorate (IDCP), whose lower reactivity allows it to selectively activate certain disarmed n-pentenyl glycosides [44],... 

To 0.5 mmol of the urethane (e.g 1), dissolved in 15 mL of dry dioxane, 3.5 equiv of iodonium dicollidine perchlorate are added to the refluxing solution in three portions in 45 minutes. The solution is then evaporated to dryness and the residue redissolved in Et20. After washing with 0.5 N HCI, sodium thiosulfate and H.O, the solution is evaporated and chromatographed (silica gel) to afford the bicyclic iodourethane (e.g., 2) in about 70-80% yield. 

In analogy to this approach, the cyclization of unsaturated furanosides and pyranosides, performed with iodonium dicollidine perchlorate [I(collidine)2C104] in dichloromethane, allows ris-2,5-disubstituted tetrahydrofurans to be obtained in moderate yield and with good to high diastereoselection122 -124. 

Abbreviations Ac acetyl Bn benzyl BSP 1-benzenesulfinyl piperidine BTIB bis(trifluoroacetoxy)iodobenzene DAST (diethylamino)sulfur trifluoride DDQ 2,3-dichloro-5,6-dicyano-/)-benzoquinone DMDO dimethyldioxirane DMTSF dimethyl(methylthio)sulfonium tetrafluoroborate DMTST dimethyl(methylthio)sulfonium triflate DTBMP 2,6-Ai-tert-butyl-4-methylpyridine DTBP 2,6-di-tert-butylpyridine DTBPl 2,6-di-tert-butylpyridinium iodide FDCPT l-fluoro-2,6-dichloropyridinium triflate FTMPT l-fluoro-2,4,6-trimethylpyridinium triflate IDCP iodonium dicollidine perchlorate IDCT idonium dicollidine triflate LPTS 2,6-lutidinium p-toluenesulfonate LTMP lithium tetramethylpiperidide Me methyl MPBT S-(4-methoxyphenyl) benzenethiosulflnate NBS A-bromosuccinimide NIS A-iodosuccinimide NlSac A-iodosaccharin PPTS pyridinium p-toluenesulfonate TBPA tris(4-bromophenyl)ammoniumyl hexachloroantimonate Tf trifluoromethanesulfonyl TMTSB methyl-bis(methylthio)sulfonium hexachloroantimonate TMU tetramethylurea Tr trityl TTBP 2,4,6-tri-tert-butylpyrimidine. 

These glycosylation reactions are promoted by NBS, iodonium dicollidine perchlorate (IDCP) or the corresponding triflate (IDCT) [353]. Iodine has also been reported to promote the reaction [254]. NIS, in combination with catalytic amounts of a protic acid such as TfOH [213], or Lewis acids such as TESOTf [17], Sn(OTf>2 [354] or BF3-Et20 [355], was introduced as a more active catalyst. Recently, glycosylation with NIS under microwave irradiation has been developed [356]. 

Veeneman, G H, van Boom, J H, An efficient thioglycoside-mediated formation of a-glycosidic linkages promoted by iodonium dicollidine perchlorate. Tetrahedron Lett., 31, 275 - 278, 1990. 

When n-halosuccinimides (NBS, NIS) are used alone without added acid catalyst, the NPG couplings are relatively slow, often requiring hours or days for completion [15], A promoter of intermediate potency that has been useful in some cases is iodonium dicollidine perchlorate (IDCP) [16], IDCP is not commercially available, but it is easily prepared as a stable crystalline salt by the procedure of Lemieux and Morgan [17]. It has found success for coupling some reactive (armed) NPGs [16], but is not potent enough for use with unreactive (disarmed) NPGs. For this, NIS/EtjSiOTf must be employed (Scheme 6). 

Other methods of preparation of these valuable compounds are shown in O Scheme 3. All of them are based on the intramolecular glycosylation of glycals by a terminal hydroxyl group. Treatment of the 3,4-di-O-benzoyl-D-glucal (4 R = Bz) with iodonium dicollidine perchlorate (IDCP) results in formation of the anhydro derivative 5a (R = Bz), while activation of the hydroxyl group in a free glycal (4 R = H) with (Bu3Sn)20 followed by iodocyclization pro-... 

Thio-sugars [60,61] are excellent glycosyl donors for oligosaccharide synthesis. Excellent reactivity of activated thioglycosides [62,63] by common promoters such as methyltriflate, dimethyl(methylthio)sulfonium triflate (DMSTS), iodonium dicollidine perchlorate (IDCP), and A-iodosuccininude (NIS) alone or with a combination of triflic acid or silver triflate makes them versatile glycosylation donors. 

Alkylation with dibutyltin acetal. h Iodonium dicollidine perchlorate. 

Pentenyl glycosides with a benzyl protection at C 2 are activated by iodonium dicollidine perchlorate and converted to glycosylating agents by the mechanism depicted in Fig. 10.3 (Mootoo et al. 1988). There is no activation with an acetyl protection at C-2. Thus, a pentenyl 2-O-acetylglycopyanoside with a free hydroxyl group behaves as an acceptor. But it may be converted to a glycosyl donor in the next step after de-O-acetylation and 0-benzylation. 

R = Me) (Lafont and Descotes 1988). The amino glycoside is then obtained by hydrazinolysis. Treatment of protected glycals with benzenesulfon-amide and iodonium dicollidine perchlorate gave compounds 10.49. Again, the corresponding aziridines were not isolated but the expected product of opening... 

Initially, the method was based on the differential reactivity conferred on each of the partners by the nature of the protecting groups and by the intrinsic nucleophilicity of the thioaryl leaving groups. However, as the method evolved, it became clear that the choice of the promoter was also an important factor to take into consideration. Indeed, it was demonstrated that a disarmed thioglycoside could be activated in the presence of powerful thiophilic promoters such as A-iodosuccinim-ide/trifluoromethanesulfonic acid (NIS/TfOH), whereas it remained inactivated in the presence of weak thiophilic reagent such as iodonium dicollidine perchlorate or methyl triflate [43,45]. 

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