[4885-02-3] · C2H4Cl2O · Dichloromethyl Methyl Ether · (MW 114.96)
(carbon monoxide equivalent in reactions with boranes and borinates; formylating reagent for aromatic compounds and vinylsilanes; formation of a-keto acid chlorides)
Alternate Names: dichloromethoxymethane; DCME.
Physical Data: bp 85 °C; d 1.271 g cm-3.
Solubility: sol most common organic solvents.
Form Supplied in: commercially available in 98% purity.
Preparative Method: from Methyl Formate and Phosphorus(V) Chloride.1
Purification: by distillation.
Handling, Storage, and Precautions: dichloromethyl methyl ether is moisture sensitive, a lachrymator, and a suspect carcinogen. Handle in a fume hood.
Dichloromethyl methyl ether functions as a carbon monoxide equivalent in the reaction with boranes to yield tertiary alcohols. The reaction works well with both symmetrical and unsymmetrical boranes and for boranes containing tertiary alkyl groups (eq 1).2,3 Hindered lithium alkoxides are the preferred bases.
A similar reaction occurs with borinate esters to yield ketones.4 This reaction has been used in a facile synthesis of bicyclo[3.3.0]nonan-9-one from 9-Borabicyclo[3.3.1]nonane (eq 2).5 The insertion reaction proceeds with retention of configuration of the migrating alkyl groups and provides a route to optically active ketones from chiral borinates and boronates (eq 3).6 This reaction is applicable to the enantioselective synthesis of a-alkynyl ketones7 and alkenones,8 and as in the reaction of boranes with dichloromethyl methyl ether, hindered lithium alkoxides are the preferred bases. Borinates also undergo an elimination-rearrangement reaction to yield alkenes on treatment with dichloromethyl methyl ether and heat or Silver(I) Nitrate (eq 4).9
Dichloromethyl methyl ether has been used extensively to formylate aromatic compounds.10-12 The reaction works well for the formylation of arenes and heterocycles such as indoles and pyrroles. Titanium(IV) Chloride has generally been used as the Lewis acid but an improved procedure recommending Tin(IV) Chloride has been reported.13 A typical example is shown in eq 5.14
Vinylsilanes are formylated by reaction with dichloromethyl methyl ether, providing a route to a,b-unsaturated aldehydes (eq 6).15,16 This reaction is also works well for the synthesis of dienals from 1-trimethylsilyl-1,3-dienes.17
Dichloromethyl methyl ether is used in the preparation of a-keto acid chlorides. Conventional reagents such as oxalyl chloride or phosphorus halides give poor results (eq 7).18
Kevin E. Henegar
The Upjohn Company, Kalamazoo, MI, USA