· Aluminum Iodide
· (MW 407.72)
(cleavage of O-N and S-O bonds;1 reductive dehalogenation of a-halocarbonyls;2 deoxygenation of epoxides and vicinal diols;3,4 ether, acetal, and ester cleaving reagent;5 iodination of allylic, benzylic, and tertiary alcohols;4a hydroiodination of alkenes and alkynes;6 Friedel-Crafts catalyst7)
Physical Data: mp 191 °C; bp 382 °C; d 3.98 g cm-3.
Solubility: sol CS2, alcohols, ether, liq. NH3.
Form Supplied in: white leaflets if pure; commercial grade yellowish to blackish-brown lumps. Exists as the dimer (Al2I6) in solid and gas phases.
Preparative Method: some applications require freshly prepared AlI3. This is conveniently done by heating clean Aluminum foil with Iodine in dry MeCN or CS2 under nitrogen with refluxing for 3 h or until the iodine color disappears. The solution obtained can be directly used for the reaction.
Handling, Storage, and Precautions: use in a fume hood; fumes in moist air; strong exothermic reaction with H2O; corrosive; moderately toxic. Keep tightly closed and protected from light.
Cleavage of N-O and S-O Bonds.
AlI3 in MeCN is a general reagent for deoxygenation of N-arylnitrones, azoxybenzenes, and N-arene N-oxides in high yield.1a It provides an efficient and facile preparation of o-aminobenzophenones by a highly selective reductive cleavage of O-N bonds in 2,1-benzoisoxazoles (eq 1).1b Chromone 3-aldonitrones are converted by a facile AlI3-catalyzed rearrangement to the 3-carboxamides.1c Ketoximes undergo Beckmann rearrangement to the carboxamide while aldoximes are readily dehydrated to the nitrile in the presence of AlI3.1d Aryl or alkyl sulfonyl chlorides and sulfoxides are reduced to the disulfide and sulfide, respectively.1e
Cleavage of C-X and C-O Bonds.
In the AlI3-mediated reductive dehalogenation of a-halocarbonyl compounds, aluminum enolates are readily generated and can be trapped via aldol reactions (eq 2).2 The deoxygenation of oxiranes with AlI3 proceeds at room temperature in MeCN or benzene to give high yields (typically >90%) of alkenes.3 With less reactive epoxides the iodohydrin can be isolated. Certain vicinal diols (cis and trans secondary-tertiary and allylic bis-secondary) are converted to the alkene by this reagent (eq 3).4a Bis-secondary vic-diols remain unchanged.
AlI3 is a highly regioselective ether cleaving reagent, in some cases having a novel cleavage pattern.5a Aryl alkyl ethers are cleaved with 1 equiv AlI3 to give the phenol and alkyl iodide. Selective ether cleavage is possible in the presence of benzoate esters. This method can be improved by the addition of quaternary ammonium iodide salts which give higher yields in shorter reaction times.5b AlI3 exhibits superior regioselectivity over Aluminum Chloride or Aluminum Bromide in the cleavage of epoxides to the halohydrin.5c It is also an efficient reagent for deprotection of a wide variety of carboxylic esters (2 equiv AlI3).5d Phenol esters, however, undergo Fries rearrangement. A nonaqueous procedure for
conversion of acetals to the carbonyl compound is provided using this reagent.5e Thioacetals are unreactive under these conditions. Allylic, benzylic, and tertiary alcohols are regioselectively converted to the corresponding iodide by AlI3. Saturated primary and secondary alcohols are unaffected. Aryl methyl ethers were shown to survive at short reaction times.4a
Good yields of hydroiodinated product are formed by treatment of alkenes and alkynes with AlI3 and H2O via in situ generation of Hydrogen Iodide.6 The use of AlI3 as a Friedel-Crafts catalyst is limited since it frequently gives lower yields than either AlCl3 or AlBr3. One exception occurs in the isopropylation of benzene.7 An interesting AlI3-catalyzed addition of MeCN has been reported (eq 4) but this does not appear to be a general reaction.8
- 1. (a) Konwar, D.; Romesh, C.; Boruah, R. C.; Sandhu, J. S. S 1990, 337. (b) Konwar, D.; Boruah, R. C.; Sandhu, J. S. CI(L) 1989, 191. (c) Mahajan, A. R.; Boruah, R. C.; Sandhu, J. S. CI(L) 1990, 261. (d) Konwar, D.; Boruah, R. C.; Sandhu, J. S. TL 1990, 31, 1063. (e) Babu, J. R.; Bhatt, M. V. TL 1986, 27, 1073.
- 2. Borah, H. N.; Boruah, R. C.; Sandhu, J. S. CC 1991, 154.
- 3. (a) Halton, B.; Russell, S. G. G. JOC 1991, 56, 5553. (b) Sarmah, P.; Barua, N. C. TL 1988, 29, 5815.
- 4. (a) Sarmah, P.; Barua, N. C. T 1989, 45, 3569. (b) Broome, J.; Brown, B. R.; Summers, G. H. R. JCS 1957, 2071.
- 5. (a) Bhatt, M. V.; Babu, J. M. TL 1984, 25, 3497. (b) Andersson, S. S 1985, 437. (c) Eisch, J. J.; Liu, Z.-R.; Ma, X.; Zheng, G.-X. JOC 1992, 57, 5140. (d) Mahajan, A. R.; Dutta, D. K.; Boruah, R. C.; Sandhu, J. S. TL 1990, 31, 3943. (e) Sarmah, P.; Barua, N. C. TL 1989, 30, 4703.
- 6. Dutta, D. K.; Lekhok, K. C.; Boruah, R. C.; Sandhu, J. S. CI(L) 1991, 175.
- 7. Kline, E. R.; Campbell, B. N.; Spaeth, E. C. JOC 1959, 24, 1781.
- 8. Sammes, P. G.; Swanson, A. G.; Whitby, R. J. JCR(S) 1988, 162.
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