Iodonium perchlorate

Amino sugars. Glycals undergo addition with the iodonium perchlorate and 2-(trimethylsilyl)ethanesulfonamide to afford 2-iodo-l-sulfonamide adducts which are transformed into the protected aminoglycosides on alcoholysis. 

The reaction of the cyclic hindered iodonium perchlorate (46) with triphenylphosphine led unexpectedly to the vinyl iodide (75) as the major product, along with the expected vinylphosphonium salt (76). This result was explained by the formation of an iodophosphonium intermediate (77) which follows two different pathways for the ligand coupling process.i (Scheme 5.6)... 

Bielawska and Michalska [511] have introduced S-(2-deoxyglycosyl)phosphor-othioates as glycosyl donors. Activation of these compounds for glycosidation with silver salts (AgF, AgC104 or AgOTf) resulted in the formation of 2 -deoxydisacchar-ides as anomeric mixtures. Thiem and coworkers reported [507] an efficient activation method for S-(2-deoxyglycosyl)phosphorothioate donors 102 by using N-iodo-succinimide (NIS) or iodonium bis(2,4,6-trimethylpyridine) perchlorate (IDCP) (Scheme 4.94). 

An elecrophilic Br+ or I+ can be successfully transferred to hydroquinidine (13) and two of its commercially available derivatives (4-chlorobenzoate and 9-phenanthryl ether hydroquinidines) simply by mixing two equivalents of the hydroquinidine with one equivalent of sym(co d ne)2-X+ perchlorate in methylene chloride or acetonitrile. H NMR studies (31) showed that the iodonium ion was associated with the nitrogen at the quinuclidine portion of the hydroquinidine instead of the aromatic nitrogen and also that all of the sym-collidines were removed from the X+ since only free collidine and no collidine-I+ peaks were observed. The (hydroquinidine)2-halonium ion is stable in solution for more than 30 minutes at room temperature these ions (and their parent amines) are more soluble in methylene chloride than in acetonitrile, and having R group other than hydrogen also improves the solubility. 

Scheme 5.1 Mechanism of thioglycoside activation (a) by thiophiles X1 such as /V-bromosuccinimicle (NBS), 11,12 methyl triflate,13 dimethyl(methylthio)sulfonium triflate (DMTST),14 phenylselenyl triflate (PhSeOTf),17,18 iV-iodosuccinimide/triflic acid (MS/TfOH),19 20 and iodonium di-sym-collidine perchlorate (IDCP)21 (b) by tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBPA,+)25 and (c) via anomeric sulfoxides.26 The stereochemical outcome of these glycosylations follows the same general trends as with many other glycosyl donor/promoter combinations (m-CPBA = mcta-chloroperbenzoic acid).

Scheme 5.7 (a) Mechanism of the w-pentenyl glycoside-based glycosylation method. Electrophiles commonly employed include iodonium di-sym-collidine perchlorate (IDCP) and A-iodosuccinimide/triethylsilyl triflate (NIS/Et3SiOTf) (b) Mechanism for the activation of NIS by EtsSiOTf.55... 

A promoter of intermediate potency is iodonium di-vym-collidinc perchlorate (IDCP), which was successfully used for coupling reactive (armed) NPGs.62 A problem is that some IDCP-promoted reactions tend to stall, leaving substantial amounts of unreacted starting material, an effect probably caused by liberation of collidine during the course of the reaction. 

Iodine-copper(II) acetate, 267 Iodine-mercury(II) oxide, 267-268 Iodine monochloride, 268-269 Iodine-silver carboxylates, 268 Iodine-silver nitrate, 268 lodoamination, 265-266 Iodocarbamation, 264-265 Iodocarbonates, 263 2 Iodoestradiol, 267 2-Iodoestrone, 267 Iodoiactonization, 263-264 C,-Iodomethylcephalosporins, 273 Iodonium di-svm-collidine perchlorate, 269 19-Iodononadecanic acid, 488 Iodophenylbis(triphenylphosphine)palladium, 269... 

Lemieux and Thiem developed the iodine glycosylation.16 You need an I+-reagent e. g. Y-iodosuccinimide (l-iodo-2,5-pyrrolidinedione, NIS) (47) or I(coll)2 (iodonium di-.sym-collidine perchlorate) (48). The mechanism of this step with the bromine reagent of 48 was evaluated by Brown. 1... 

The first step is a reversible dissociation of 48 into free collidine (49) and a reactive intermediate, coll-I+ (50). The electrophilic collidine-iodonium cation forms with glycal 16 the cyclic compound 52. The perchlorate anion of 48 is not nucleophilic enough to attack the sustained intermediate 52, but 52 is captured by nucleophilic attack of benzenesulfonamide (51). This attack proceeds from the back and leads to trans product 17. 

Anodic iodination 24°) involves an iodonium intermediate, probably N-iodo-acetonitrilium perchlorate (29) undergoing electrophilic aromatic substitition (Eq. (100) ). A radical cation (28) as intermediate is improbable in this case. Electrolysis of iodine and aromatics in CH3CN/LiC104 yields the corresponding... 

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],... 

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