{{Unreferenced, date=November 2021
A crotyl group is an organic
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the res ...
with the formula RCH2CH=CHCH3. Systematically, it is called a but-2-en-1-yl group and exhibits
geometric isomerism
Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
, being either ''cis'' (''Z'') or ''trans'' (''E''). There are many simple compounds in which the crotyl group forms base carbon chain:
crotyl alcohol
Crotyl alcohol, or crotonyl alcohol, is an unsaturated alcohol. It is a colourless liquid that is moderately soluble in water and miscible with most organic solvents. Two isomers of this alcohol exist, cis and trans.
It can be synthesized by th ...
,
crotonaldehyde
Crotonaldehyde is a chemical compound with the formula CH3CH=CHCHO. The compound is usually sold as a mixture of the ''E''- and ''Z''-isomers, which differ with respect to the relative position of the methyl and formyl groups. The ''E''-isome ...
,
crotonic acid
Crotonic acid ((2''E'')-but-2-enoic acid) is a short-chain unsaturated carboxylic acid, described by the formula CH3CH=CHCO2H. It is called crotonic acid because it was erroneously thought to be a saponification product of croton oil. It crysta ...
2-butene
But-2-ene is an acyclic alkene with four carbon atoms. It is the simplest alkene exhibiting ''cis''/''trans''-isomerism (also known as (''E''/''Z'')-isomerism); that is, it exists as two geometric isomers ''cis''-but-2-ene ((''Z'')-but-2-ene) and ...
(either isomer): this reaction must be performed in the presence of organometallic reagents, as a base, usually
alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloal ...
lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...
, 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 reactions
Crotylation readily occurs with
alkoxy
In chemistry, the alkoxy group is an alkyl group which is singularly bonded to oxygen; thus . The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the organic compound ethyl phenyl ether (, also ...
boronates to form crotylboronates.
Crotylboronates are useful reagents in the formation of crotyl alcohols. They react with the acidic protons of
aldehydes
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
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.
Alkenyl groups