[75-30-9] · C3H7I · 2-Iodopropane · (MW 170.00)
(heterolytic and homolytic alkylating agent; mediator of thiocarbonate conversion to alkenes; can add across carbon-carbon triple and double bonds; used in the preparation of the a-isopropoxymethylene blocking group)
Alternate Name: isopropyl iodide.
Physical Data: mp -90 °C; bp 88-90 °C; d 1.073 g cm-3.
Form Supplied in: colorless liquid; stabilized with copper.
Purification: the reagent can be washed with aqueous Na2S2O3 or NaHSO3, then water, dried over magnesium sulfate and distilled at slightly reduced pressure. Alternately, the reagent can be simply filtered through a plug of activated alumina.1
Handling, Storage, and Precautions: the reagent is a cancer suspect agent and should be handled in a fume hood with protective gloves. Storage in the dark over a small quantity of mercury is recommended.
2-Iodopropane is commonly employed as an alkylating agent toward, for example, the anions of esters,2 nitriles,3 sulfones,4 phenols,5 and pyrroles.6 a,b-Unsaturated esters7 and amides8 undergo a-alkylation. Monoalkylation of the dianions of b-keto esters,9 b-ketophosphonates,10 and the trianion of Boc-protected glycine11 has been achieved. The asymmetric alkylation of the sultam-derived glycinate equivalent (1) has been reported (eq 1).12 An enantioselective synthesis of 3-substituted 2-keto esters has been achieved by the SAMP hydrazone method (eq 2).13 A method for replacement of the N-methyl group of codeine (2) with an isopropyl group has been reported (eq 3).14
4-Methylpyridine (3) on protonation undergoes regioselective alkylation with 2-iodopropane in the presence of Hydrogen Peroxide and an Fe2+ salt (eq 4).15
Heating the thiocarbonate (4) in neat 2-iodopropane at reflux afforded the corresponding iodo thiocarbonate. Subsequent reduction with Zinc dust provided the alkene (5) in good overall yield (eq 5).16
Triethylborane induced addition of 2-iodopropane to alkynes17 and vinylsilanes18 has been reported (eqs 6 and 7). Similarly, the former process can also be induced with Triphenylstannane.19
The ketone (6) has been methylated at the more sterically congested site by the use of the isopropoxymethylene blocking group (eq 8).20
Peter D. Wilson
The Ohio State University, Columbus, OH, USA