Crotyl group

[1] Systematically, it is called a but-2-en-1-yl group and exhibits geometric isomerism, being either cis (Z) or trans (E).

Crotylate (crotyl anions) can be synthesised from 2-butene (either isomer): this reaction must be performed in the presence of organometallic reagents, as a base, usually alkyl lithium, or any alkylates of s-block metals, in a solvent, typically THF, and at low temperatures, generally below -20 °C.

The negative charge is delocalised over three of the carbon atoms of the crotylate group and there is resonance between the two possible delocalised forms (one for each terminal carbon).

Crotylation readily occurs with alkoxy boronates to form crotylboronates.

They react with the acidic protons of aldehydes to form alcohols.