IDCP: 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],... 

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]. 

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. 

Other promoters (MeOTf, NIS, iodonium dicollidine perchlorate (IDCP), and iodonium dicollidine triflate (IDCT)) have also been investigated, but DMTST usually seems to be the right choice [16]. 

Alternatively, Mootoo and coworkers [82,83] have developed a two-step iodoether-ification/Ag-catalyzed cychzation method for the synthesis of spiroacetals from homoallyhc alcohols 150 (Scheme 37). Treatment of the diol with iodonium dicollidine perchlorate (IDCP), followed by exposure to silver triflate in the presence of collidine affords the spiroacetals 154 in moderate to good yield as diastereomeric mixtures. This method was most recently applied in their synthesis of a simplified monensin analogue, polyether spiroacetal 156 [84]. Thus, two-step treatment of diol 155 under the established conditions provided spiroacetal 156 as a 2 1 mixture of epimers. 

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