Eschenmoser's salt

In organic chemistry, Eschenmoser's salt is the ionic, organic compound. It is the iodide salt of the dimethylaminomethylene cation.
The dimethylaminomethylene cation is a strong dimethylaminomethylating agent, used to prepare derivatives of the type. Enolates, silyl enol ethers, and even more acidic ketones undergo efficient dimethylaminomethylation. Once prepared, such tertiary amines can be further methylated and then subjected to base-induced elimination to afford methylidenated ketones. The salt was first prepared by the group of Albert Eschenmoser after whom the reagent is named.

Structure and bonding

Dimethylaminomethylene cation is described as a resonance hybrid of the carbocation and an iminium cation:
The atoms are coplanar. The cation is isoelectronic with isobutene.

Preparation

Pyrolysis of iodomethyltrimethylammonium iodide affords the desired salt:
An alternative route starts with bismethane:

Related salts

Other salts of the dimethylaminomethylene cation:

Dimethylammonium trifluoroacetate.
Dimethylammonium chloride