Ethers dichloromethyl methyl, reaction with aromatic

Besides 1-15 to 1-17, several other formylation methods are known.302 In one of these, dichloromethyl methyl ether formylates aromatic rings with Friedel-Crafts catalysts.303 ArCHClOMe is probably an intermediate. Orthoformates have also been used.304 In another method, aromatic rings are formylated with formyl fluoride HCOF and BF3.305 Unlike formyl chloride, formyl fluoride is stable enough for this purpose. This reaction was successful for benzene, alkylbenzenes, PhCl, PhBr, and naphthalene. Phenols can be regioselectively formylated in the ortho position in high yields by treatment with two equivalents of paraformaldehyde in aprotic solvents in the presence of SnCL and a tertiary amine.306 Phenols... 

The synthesis of dichloromethyl methyl ether has been included because of its usefulness as a reagent for the preparation of aromatic aldehydes (Expt 6.115). It is readily obtained by the reaction of phosphorus pentachloride in admixture with phosphorus oxychloride with methyl formate (Expt 5.71). 

Aldehyde synthesis [before references]. A fairly general route to aromatic aldehydes is illustrated by the synthesis of mesitylaldehyde by TiCl4-catalyzed reaction of mesitylene with dichloromethyl methyl ether (which see, this volume). 

FormyMestannylation. A trimethylstannyl group attached to an aromatic ring or an alkenyl position is liable to replacement on reaction with dichloromethyl methyl ether. Aldehydes are formed. 

Gross and Mirsch found that reaction of aromatics with dichloro methyl methyl sulfide and aluminum chloride yield aromatic aldehydes. However, the yields were lower compared to using dichloromethyl ethers as formylating agent. Cumene aldehyde was obtained in a 41%, mesityl aldehyde in 49% and 2-naphthyl aldehyde in 52% yield (Eq 1.16). 

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