[3756-30-7] · C4H7I · Methallyl Iodide · (MW 182.01)
(unstable but reactive alkylating agent attacking C, N, and S nucleophiles; the products are susceptible to addition reactions, especially electrophilically, across C=C systems)
Physical Data: golden-yellow liquid; bp 116-118 °C (dec), 37-40 °C/29 mmHg, 25-30 °C/3-5 mmHg.
Solubility: misc most organic solvents; sparingly misc aqueous media.
Preparative Methods: prepared from Methallyl Chloride by reaction with Sodium Iodide in acetone, MEK, or DMF.
Purification: wash with aq. Na2S2O3; dry, and distill under reduced pressure.1a
Handling, Storage, and Precautions: sensitive to light and heat; prepare as required; decomposes appreciably after a few hours. Use in a fume hood.
The major reported use of methallyl iodide is as an allylating agent when its reactivity outweighs its sensitivity to light and heat.1 The expected chemical reactions are those of the other methylallyl halides and, by extension, those of allyl halides. N-Alkylation occurs with iodo lactams2 and with indoles.3 N,O-Diacetylhydroxylamine is also N-methallylated when Potassium Carbonate is added to a solution of it and methallyl iodide in DMF; the methallyl iodide is preformed from the chloride and NaI in DMF (rt, 3 h; 91% conversion to the iodide).4 Li derivatives of silylated acrylate esters (deprotonated by Methyllithium) are specifically attacked on C by substituted allyl iodides.5 2-Cyclohexenone derivatives6,7 give 6-(methallyl) derivatives via the corresponding carbanion (eq 1).
The crystalline Na enolate salts of 2,4-pentanedione derivatives similarly undergo specific (meth)allylation at C-3 using aprotic solvents such as DMSO.8 The carbanion derived (LDA-THF-HMPA, -75 °C) from methyl crotonate apparently undergoes a-attack with an allylic shift (eq 2).9
Stereoselective attack occurs with chiral half-esters of methylmalonic acid, using Lithium Diisopropylamide (2 mole) and RI (R = allyl, methallyl).10 Similarly, the glycine enolate synthon (1) has been used to provide a-(methallyl)glycine in a remarkably stereoselective process.11
Friedel-Crafts alkylation of benzene and other simple arenes may be brought about with Lewis acids (e.g. Aluminum Chloride, Boron Trifluoride) but (meth)allyl iodide with Cl3CCO2Ag (20 °C; 2 h) attacks benzofuran at both the 2- and 3-positions, though benzothiophene is allylated only at C-2.12
University of Surrey, Guildford, UK