Crotyl group
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A crotyl group is an organic functional group with the formula {{chem2|RCH_{2}CH\dCHCH_{3}|}}.{{Cite Merriam-Webster|crotyl}} Systematically, it is called a but-2-en-1-yl group and exhibits geometric isomerism, being either cis (Z) or trans (E). There are many simple compounds in which the crotyl group forms base carbon chain: crotyl alcohol, crotonaldehyde, crotonic acid, and crotyl acrylate are examples.
Synthesis of {{chem name|crotylates}}
{{chem name|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 {{chem name|crotylate}} group and there is resonance between the two possible delocalised forms (one for each terminal carbon).
Crotylation reactions
Crotylation readily occurs with alkoxy boronates to form {{chem name|crotylboronates}}.
{{chem name|Crotylboronates}} are useful reagents in the formation of crotyl alcohols. They react with the acidic protons of aldehydes to form alcohols. The mechanism involves a six-membered ring involving the carbonyl oxygen and boron in a chair-like structure. Such reactions are highly diastereoselective.