Iodine-mediated reactions

Diels-Alder reaction of N-allylic enamides and lactam derivatives through iodine-mediated activation [98]... 

Kanny G, Pichler W, Morisset M, et al T-cell-mediated reactions to iodinated contrast media evaluation by skin and lymphocyte activation tests. J Allergy Clin Immunol 2005 115 179-185. 

Such reactions are also possible in vitro, as several mild oxidizing agents are at hand nowadays. Thus, the Dess-Martin periodinane (DMP) [50] has been proven to be a versatile and powerful reagent for the mild oxidation of alcohols to the corresponding carbonyl compounds. In this way, a series of new iodine(V)-mediated reactions has been developed which go far beyond simple alcohol oxidation [51], Ni-colaou and coworkers have developed an effective DM P-mediated domino polycy-clization reaction for converting simple aryl amides, urethanes and ureas to complex phenoxazine-containing polycycles. For example, reaction of the o-hydroxy anilide 7-101 with DMP (2 equiv.) in refluxing benzene under exposure to air led to polycycle 7-103 via 7-102 in a yield of 35 % (Scheme 7.28) [52]. 

TABLE 5-1. Iodine-Mediated Asymmetric Diels-Alder Reaction of ( + )-44... 

In addition to the procedures listed in Table 3.38, further reactions have been used to generate halides upon cleavage. In Section 3.5.2, iodolactonization is presented as a method for the preparation of iodomethyl lactones from resin-bound pentenoic or hexenoic acid derivatives. Closely related to the iodolactonization is the iodine-mediated formation of 2-(iodomethyl)tetrahydrofurans from resin-bound isoxazoli-dines (Entry 9, Table 3.38 for the mechanism, see Figure 15.5). Nitriles can also be prepared by cleavage and simultaneous dehydration of amides RCONH2 from the Rink or Sieber linkers with TFA anhydride (Entry 10, Table 3.38). 

The survey is intended to cover the published literature on the subject as fully as possible. Although the four halogens are well known as constituents of a wide range of carbohydrate compounds, radical-mediated halogenations have, in most cases, been realized only with bromine. There are, however, some examples of chlorinations to the best of our knowledge, there are no reported fluorinations or iodinations which occur by direct, radical-mediated processes. The radical-mediated reactions by which bromodeoxy carbohydrates are obtainable from benzylidene acetals17-19 are not considered. 

Copper(I) mediated reactions of alkenyliodonium salts with nucleophiles proceed with complete retention of configuration, which is probably explained by the mechanism involving oxidative addition of cuprates, ligand coupling at the iodine center of 67, and then ligand coupling at the copper(III) of 68 (Scheme 31) [42,54]. 

Pioneering studies on hypervalent iodine-induced reactions toward total syntheses of several natural products had been reported from the 1970s to the early 1980s. That is, Kishi and co-workers accomplished the total synthesis of sporidesmin A (120), which is a toxic metabolite of Pithomyces chartarum, by PIDA-mediated cyclization of tryptamine derivative 121, but, the yield of tricyclic compound 122 was only 30% [85] (Scheme 1). 

Other applications of iodine(III)-mediated reactions toward total syntheses of bioactive alkaloids such as salutaridine (123), (-)-codeine (124), and 6a-epipretazettine (125) were reported by White et al. and Szantay et al. in the early 1980s [46-48] (Schemes 2-4). 

Iodine-mediated removal of both prenyl protecting groups from aryl ether 506 leads to the unexpected formation of 3-(3-iodo-2,2-dimethylchroman-6-yl)propan-l-ol. The reaction proceeds via formation of the ortho-allylic phenol intermediate 507 by electrophilic removal of a prenyl species, followed by an iodine promoted electrophilic cycliza-tion (Scheme 111) <2001SL1989, 2002T5689>. 

The Schmitz reaction can be unsuccessful in sterically demanding environments in such circumstances, the electrophilic aminating agent reacts faster with ammonia than with hindered ketones <1965JA2665>. Consequently, the synthesis of 2-azi-camphane 64, a compound which is unobtainable under standard conditions <1996TL6647>, was achieved by slow diaziridination of camphor imine hydrochloride 63 (rather than camphor itself) with hydroxylamine-O-sulfonic acid (HOSA)-ammonia, followed by iodine-mediated oxidation (Scheme 22) <2001S379>. 

Scheme 6.3 Mechanism of Et3B-mediated iodine transfer reaction.

The Bohlmann-Rahtz reaction is a classic pyridine synthesis that has been studied and modified in many ways. Bagley et al. has elaborated on his previous work and reported an iodine-mediated catalytic Bohlmann-Rahtz reaction of aminodienone intermediates <05SL649>. This modified process is reported to be rapid at ambient temperatures resulting in good yields. Moreover, Bagley and co-workers presented a one-pot, three-component Bohhnann-Rahtz reaction to synthesize 2,3,6-trisubstituted and 2,3,4,6-tetrasubstituted pyridines 8 and 9 from P-ketoesters 10 and alkynes 11 as shown in Seheme 3 <05JOC1389>. 

In an Arbuzow reaction phosphite tricsters can be immobilized to obtain phosphorothiolates. Iodine-mediated transesterification of phosphorothiolates leads to cyclic phosphate of oligonucleotides [238],... 

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