[78-88-6] · C3H4Cl2 · 2,3-Dichloropropene · (MW 110.97)
(general purpose alkylating agent)
Physical Data: bp 94 °C; nD 1.4611; d 1.204 g cm-3.
Form Supplied in: colorless liquid; widely available.
Preparative Method: can be prepared from 1,2,3-trichloropropane in 87% yield by the elimination of hydrogen chloride, using NaOH in a refluxing aqueous or ethanolic solution.1 Recently it has been shown that the addition of quaternary basic salts such as [Me(CH2)7]3
Handling, Storage, and Precautions: highly flammable liquid (fp 10 °C); toxic; corrosive. Use in a fume hood.
2,3-Dichloropropene (1) is a general purpose alkylating agent, useful for the incorporation of allyl side chains. Additions to carbonyl enolate anions are common,3,4 for instance in the final stages of the total synthesis of (-)-hypnophilin (eq 1).5
The additions of (1) to alcohols,6 amines,7 sulfones,8 ketimines,9 and Schiff bases10 are also known.
In a number of cases the disposition of the (2-chloro)allyl side chain allows the alkylation to be followed by a Claisen rearrangement,6,11,12 for instance in the bis(chloroallyl) ether (3) of anthrarufin (2) (eq 2).13
2,3-Dichloropropene also undergoes alkylation reactions with Grignard reagents.14-16 This has been used in the synthesis of cyclic ketones by cyclization of the allyl side chain onto an alkene using 97% Formic Acid (eq 3).17
Cyclization of alkynylanilines to indoles under palladium catalysis, in the presence of allyl chlorides, gives 3-allylindoles in good yields (eq 4).18 The reaction mixture must contain proton scavengers to avoid trapping of the intermediate organopalladium species by H+.
Although many routes to Allene are described in the literature, most give a mixture of allene and methylacetylene. However, reductive elimination of 2,3-dichloropropene with Zinc dust gives allene in a reproducible manner in good yield, with 2-chloropropene as the only impurity (eq 5).19
2,3-Dichloropropene acts as an electron acceptor in the radical coupling of aryl Grignard reagents (eq 6).20 The high yield and avoidance of toxic thallium compounds give this method an advantage over other aryl coupling reactions. This method has been extended to the production of aryl polymers. Poly(p-phenylene) (PPP) has been produced using 2,3-dichloropropene and difunctional aryl Grignards (eq 7).21
In the presence of Sodium Iodide, 2,3-dichloropropene undergoes halogen exchange in the 3-position (eq 8).22
2,3-Dichloropropene has been shown to undergo oxidative addition to form complexes with transition metals, for instance with ruthenium.23
Functionalized cyclopentanes can be prepared from vinylcyclopropanes and 3-substituted propenes (e.g. 1) by both photochemical and DBU initiation methods (eq 9).24
Michael J. Cherry
University of Cambridge, UK