Iodination nucleophilic displacement

The nucleophilic displacement of the iodine moiety in 2-iodoben-zoates mediated by triphenyltin hydride and di-n-butyltin dichloride in aqueous solution has been demonstrated (Eq. 6.16).33 For example, 2-iodobenzoic acid reacts with a toluene solution of Ph3SnH/l,3-(N02)2 C6H4/aq. NaHC03 to give 89% yield of salicylic acid. 

The reduction of (2,3)-q - and (2,3)-jS-methylenepenam j6-sulfoxides to the corresponding sulfides using potassium iodide and trifluoroacetic anhydride (TFAA) is found to be much faster than for bicyclic jS-lactam jS-sulfoxides.- In the proposed mechanism, initial attack of the sulfoxide oxygen on TFAA is followed by rate-limiting, nucleophilic displacement of trifluoroacetate by iodide ion nucleophilic attack of iodide on the iodine atom then yields the sulfide and iodine. The rate enhancement is accounted for by the stabilization of the transition state in the rate-limiting step by interaction of the p-like orbital of sulfur and the cyclopropane a orbital. 

The oxidative closure of diphenylamines has been achieved with iodine at 350°C and with platinum at 450-540 C. ° Carbon-carbon bonding via displacement of the halogen of a 2-chlorophenyl-3 -hydroxyphenylamine clearly must involve intramolecular nucleophilic displacement para to phe-noxide. ... 

These reactions are related to the reaction of aryl diazonium salts with iodide yielding iodoaryls, the mechanism of which seems to be a one-electron transfer (radical) reaction and not a nucleophilic displacement. Just as iodide is easily oxi- zed to iodine by the aryl diazonium cation, 2.4.6-triphenyl-X -phosphorin is oxidized to the radical cation 58. 

Cyclization of allylic alcohols to form epoxides has been particularly problematical, and the reactions have been more of mechanistic than of synthetic interest. For reactions conducted under basic conditions, it is possible that epoxide formation involves initial halogen addition followed by nucleophilic displacement to form the epoxide. Early examples of direct formation of epoxides from allylic alcohols with sodium hypobromite," bromine and 1.5 M NaOH,12 and r-butyl hypochlorite13 have been reviewed previously.fr Recently it has been shown that allylic alcohols can be cyclized effectively with bis(jym-collidine)iodine(I) perchlorate (equation 3).14 An unusual example of epoxide formation competing with other cyclization types is shown in equation (4).15 In this case, an allylic benzyl ether competes effectively with a -/-hydroxyl group as the nucleophile. 

A simple and efficient procedure for the direct oxidation of C-3 of l,4-benzodiazepin-2-ones, applicable to the preparation of the anxiolytic agents oxazepam and lorazepam, has been developed that represents an improvement over the well-established Polonovsky rearrangement of the N-4 oxide <20060PD1192>. Iodine in AcOH at 65 °C catalyzed acetoxylation in a reaction that involved iodination at C-3 followed by a rapid nucleophilic displacement by KOAc. The liberated HI was recycled to iodine by inclusion of a stoichiometric oxidant, with K2S2O8 being the optimal compromise of cost, availability, and efficiency. 

The Prevost Reaction allows the synthesis of anti-diols from alkenes by the addition of iodine followed by nucleophilic displacement with benzoate in the absence of water. Hydrolysis of the intermediate diester gives the desired diol.The Woodward Modification of the Prevost Reaction gives syn-diols. 

The direct iodination of methylpyridines is rare and iodomethylpyridines are generally obtained by nucleophilic displacement of existing benzylic substituents. 

In comparison with conventional nucleophilic displacement of other groups, such as chlorine, bromine and iodine, fluorodenitration is much faster. Therefore, substitution can be carried out under milder reaction conditions. In particular, lower temperatures allow the synthesis of complex, thermolabile derivatives, e.g. [ F]spiroperidol from its inactive nitro analog using rubidium [ F]fluoride. ... 

The use of /t-iodotoluene difluoride for replacement of iodine by fluorine has beeen described as a nucleophilic displacement of IF2, as a good leaving group, in a pre-formed iodoaUcane difluoride [51]. Note that iodine is displaced in preference to p-TsO in this system (Figure 3.5a). 

Similar functionalization, but at the C-3 position in levoglucosenone, via iodine addition to the conjugate position and then nucleophilic displacement of iodine with a reactive thiol represents another valuable stereoselective strategy to a/p (l-3)-linked 5>thiodisaccharides. 

Closure of 5-halo-amines by nucleophilic displacements of halogen, is complemented by the conversion of iV-chloro-pent-4-enylamines into 3-chloropiperidines by exposure to tetra-n-butylammonium iodide. The process is believed to involve conversion to an A -iodo-amine, which serves as an electrophilic source of iodine, cyclisation to a 2-(iodomethyl)-pyrrolidine, ring closure to a bicyclic aziridinium ion and ring opening via attack by chloride to produce the six-membered heterocycle. 

Iodine of the 5-iodotricyclic 274 was capable of nucleophilic displacement by methoxy-, hydroxyl-, amino-, and mercapto groups. The rearrangement of [3,4- ]-derivatives by refluxing in formamide to [5,1 - ]-analogues is seen in Scheme 81. 

Research on the 3-methyl-4-nitrofuroxan is rather hazardous, on account of its tendency to explode unexpectedly. Nucleophilic displacement of the nitro group in 4-nitrofuroxans occurs readily, and it provides a convenient route to a variety of other derivatives.95,288 Reduction of 4-nitro-3-phenyl-furoxan to the amine has been accomplished using stannous chloride.288 Some nitrofuroxans have been found to liberate iodine from sodium iodide in acetone.83,446... 

The mechanism of the elimination from the 5,6-disulfonates most probably involves nucleophilic displacement of the primary sulfonyloxy group (see other iodo-p-tolylsulfonates, on p. 101), followed by a second attack by iodide on the iodine, and by a concerted elimination of the secondary ester grouping. An elimination also occurs when 1,2-0-... 

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