Reviews and Accounts
ARKIVOC 2015 (vi) 446-493
12 Preparation of the Reagent For general application in organic synthesis, AlI3 can be prepared in situ. Colorless AlI3 crystal is available by reacting aluminum and iodine in hexane or by reacting aluminum with sublimed iodine in a vitreous pipe at 500~525 oC.189 12.1 In situ preparation of AlI3 A mixture of aluminum powder or foil (250 mg, 9.3 mmol) and elementary iodine (1.9 g, 15 mmol) were mixed in an inert solvent (benzene, toluene, acetonitrile, carbon disulfide, or cyclohexane, 8 ml). The mixture was stirred under reflux for about 3 h, till the purple color of iodine faded. The solution can be used directly without further purification.25 12.2 Preparation of crystalline AlI3 To a stirred mixture of aluminum foil (3 mmol, 0.1 mm thick) in hexane (100 ml) was added elementary iodine (4.5 mmol). Then the mixture was refluxed under slow argon flush for 1 hour until the purple color faded. Unreacted metal was filtered off while hot. After cooling to room temperature, colorless crystals precipitated and were collected, yield 96%, mp 191 oC.190
13 Conclusions AlI3 is a strong Lewis acid and iodide source. Its unique oxophilicity has been widely and extensively applied in deoxygenation and deoxydehydration of a broad range of substrates such as oxiranes, diols, sulfoxides, sulfonyl chlorides, oximes, N-arylnitrones azoxyarenes, and Nheteroarene N-oxides. It can be used in generation of aluminum enolates from -haloketones which in turn can be quenched with water to afford dehalogenated products, or be captured by unsaturated ketone affording Michael addition products. AlI3 also serves as a precursor of HI in hydroiodination of alkenes or alkynes. Generally AlI3 is not suitable for application in FriedelCrafts reactions due to its unique oxophilicity and electroaffinity character. Among the broad range of other synthetic applications, ether cleavage and ester cleavage have been frequently applied in synthesis. Non-hydrolitic ester cleavage is suitable for substrates sensitive to strong acidic or basic conditions. Efficient demethylation of alkyl aryl ethers has made AlI3 an ideal alternative to BBr3.
14 Acknowledgements The financial support from open project program of Hubei Key Laboratory of Drug Synthesis and Optimization, Jingchu University of Technology (No. OPP2015YB03) is acknowledged.
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