Magnesium Iodide


[10377-58-9]  · I2Mg  · Magnesium Iodide  · (MW 278.11)

(mild Lewis acid for Diels-Alder reaction;12 enol acetylation of ketones;14 deoxygenation of oxiranes;1 iodination and opening of epoxides and cyclopropylmethanols8,9)

Physical Data: mp (dec) <637 °C; d 4.43 g cm-3.

Solubility: sol water (1.48 g mL-1 of H2O at 18 °C); slightly sol alcohols, ethers, ammonia.

Preparative Method: mostly prepared in situ from Magnesium turnings and Iodine in refluxing ether.

Handling, Storage, and Precautions: toxicity data not available. May be harmful by inhalation, ingestion, or skin contact.

MgI2 is used in the deoxygenation of oxiranes to the corresponding alkenes via iodohydrins with retention of configuration in high yields.1

Vinyl2 and bridgehead triflates3 are converted into the corresponding iodides by reaction with MgI2, generally in nonpolar solvents such as CS2 (eq 1).

MgI2 can effect the transformation of cyclopropylcarbinols into homoallylic iodides in refluxing Et2O (eq 2).4,5 Tertiary and benzylic alcohols are more reactive than secondary. MgI2 can also be used in the regioselective opening of 2,3-epoxy alcohols and b,g-epoxy sulfones, leading to the corresponding 3-iodo-1,2-diols (eq 3) and b-hydroxy sulfones (eq 4), respectively.6,7

Treatment of silyloxiranes8 and glycidic esters9 with MgI2 results in their rearrangement to the corresponding silyl ketone (eq 5) and a-keto esters.

Carboxylic esters can be hydrolyzed with MgI2 in aprotic solvents like CS2 and toluene.10 It can also be used to demethylate a methoxy group ortho to an acyl group under mild conditions without isomerization of an isopropenyl group (eq 6).11

As a Lewis acid, MgI2 has been shown to increase the regioselectivity, having equal but opposite effect to that of Boron Trifluoride Etherate in Diels-Alder reactions of perihydroxylated naphthoquinones with 1-methoxy-3-methyl-1,3-butadiene (eq 7).12

Radical-mediated reduction of a-iodo-b-alkoxy esters with Tri-n-butylstannane in the presence of catalytic MgI2 results in excellent erythro selectivity. Threo selectivity is seen in the absence of a Lewis acid.13

MgI2.Et2O can be used as a mild Lewis acid catalyst for the enol acetylation of ketones.14

1. Chowdhury, P. K. JCR(S) 1990, 192.
2. Martinez, A. G.; Alvarez, R. M.; Fraile, A. G.; Subramanian, L. R.; Hanack M. S 1986, 222.
3. Martinez, A. G.; Vilar, E. T.; Lopez, J. C.; Alonso, J. M.; Hanack, M; Subramaniam, L. R. S 1991, 353.
4. McCormick, J. P.; Barton, D. L. JOC 1980, 45, 2566.
5. McCormick, J. P.; Barton, D. L. CC 1975, 303.
6. Banini, C.; Righi, G.; Sotgiu, G. JOC 1991, 56, 6206.
7. Najera, C.; Sansano, J. M. T 1991, 47, 5193.
8. Obayashi, M.; Utimo, K.; Nozaki, H. TL 1977, 1807.
9. Coutrot, P.; Legris, C. S 1975, 118.
10. Martinez, A. G.; Barcia, J. O.; Veccio, G. H.; Hanack, M.; Subramanian, L. R. TL 1991, 32, 5931.
11. Yamaguchi, S.; Sugiura, K.; Fukuoka, R.; Okazaki, K.; Takeuchi, M.; Kawase, Y. BCJ 1984, 57, 3607.
12. Kelly, T. R.; Montury, M. TL 1978, 4311.
13. Guindon, Y.; Lavallee, J. F.; Llinas-Brunet, M.; Horner, G.; Rancourt, J. JACS 1991, 113, 9701.
14. Chowdhury, P. K. CI(L) 1990, 9, 299.

Sanjay R. Chemburkar

Abbott Laboratories, North Chicago, IL, USA

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