thumb|right|Crotyl groups attached to R. A '''crotyl group''' is an organic functional group with the formula {{chem2|RCH_{2}CH\dCHCH_{3}|}}.<ref>{{Cite Merriam-Webster|crotyl}}</ref> 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) by deprotonation with highly basic organometallic reagents,<ref name=":1">{{Cite journal |last=Helmboldt |first=Hannes |last2=Köhler |first2=Daniel |last3=Hiersemann |first3=Martin |date=2006-04-01 |title=Synthesis of the Norjatrophane Diterpene (−)-15-Acetyl-3-propionyl- 17-norcharaciol |url=https://pubs.acs.org/doi/10.1021/ol060115t |journal=Organic Letters |language=en |volume=8 |issue=8 |pages=1573–1576 |doi=10.1021/ol060115t |issn=1523-7060|url-access=subscription }}</ref><ref name=":0">{{Cite journal |last=Batey |first=Robert A. |last2=Thadani |first2=Avinash N. |last3=Smil |first3=David V. |date=1999-07-01 |title=Potassium allyl- and crotyltrifluoroborates: Stable and efficient agents for allylation and crotylation |url=https://linkinghub.elsevier.com/retrieve/pii/S0040403999007741 |journal=Tetrahedron Letters |language=en |volume=40 |issue=23 |pages=4289–4292 |doi=10.1016/S0040-4039(99)00774-1|url-access=subscription }}</ref> typically organolithium reagents.<ref>{{Cite journal |last=Dolgoplosk |first=B.A. |last2=Beilin |first2=S.I. |last3=Vollershtein |first3=E.L. |last4=Teterina |first4=M.P. |date=1975-03-25 |title=Studies of crotyl anion reactions and some regularities of copolymerization in hexamethylphosphortriamide |url=https://linkinghub.elsevier.com/retrieve/pii/0014305775900786 |journal=European Polymer Journal |language=en |volume=11 |issue=3 |pages=287–291 |doi=10.1016/0014-3057(75)90078-6|url-access=subscription }}</ref> The negative charge is delocalised over three of the carbon atoms of the {{chem name|crotylate}} group.
==Crotylation reactions== Crotyl halides, crotyl alcohols,<ref name=":0" /> crotyl silanes,<ref>{{Cite journal |last=O'Hora |first=Paul S. |last2=Incerti‐Pradillos |first2=Celia A. |last3=Kabeshov |first3=Mikhail A. |last4=Shipilovskikh |first4=Sergei A. |last5=Rubtsov |first5=Aleksandr E. |last6=Elsegood |first6=Mark R. J. |last7=Malkov |first7=Andrei V. |date=2015-03-16 |title=Catalytic Asymmetric Crotylation of Aldehydes: Application in Total Synthesis of (−)‐Elisabethadione |url=https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.201500176 |journal=Chemistry – A European Journal |language=en |volume=21 |issue=12 |pages=4551–4555 |doi=10.1002/chem.201500176 |issn=0947-6539}}</ref><ref>{{Cite journal |last=Arefolov |first=Alexander |last2=Panek |first2=James S. |date=2005-04-01 |title=Crotylsilane Reagents in the Synthesis of Complex Polyketide Natural Products: Total Synthesis of (+)-Discodermolide |url=https://pubs.acs.org/doi/10.1021/ja043168j |journal=Journal of the American Chemical Society |language=en |volume=127 |issue=15 |pages=5596–5603 |doi=10.1021/ja043168j |issn=0002-7863|url-access=subscription }}</ref> crotonaldehyde and crotyl boronates are useful reagents for synthesizing crotyl and allyl compounds. Crotyl and allyl compounds are common intermediates in total synthesis<ref name=":1" /> due to their ability to undergo sigmatropic rearrangements.
Crotylboronates are easily made from reaction of crotyl anions with alkoxy boronates,<ref>{{Cite journal |last=Lachance |first=Hugo |last2=Lu |first2=Xiaosong |last3=Gravel |first3=Michel |last4=Hall |first4=Dennis G. |date=2003-08-01 |title=Scandium-Catalyzed Allylboration of Aldehydes as a Practical Method for Highly Diastereo- and Enantioselective Construction of Homoallylic Alcohols |url=https://pubs.acs.org/doi/10.1021/ja036807j |journal=Journal of the American Chemical Society |language=en |volume=125 |issue=34 |pages=10160–10161 |doi=10.1021/ja036807j |issn=0002-7863|url-access=subscription }}</ref><ref>{{Cite journal |last=Tan |first=Qiuyuan |last2=Wang |first2=Xinqiao |last3=Xiong |first3=Yang |last4=Zhao |first4=Zimeng |last5=Li |first5=Lu |last6=Tang |first6=Pei |last7=Zhang |first7=Min |date=2017-04-18 |title=Chiral Amino Alcohol Accelerated and Stereocontrolled Allylboration of Iminoisatins: Highly Efficient Construction of Adjacent Quaternary Stereogenic Centers |url=https://onlinelibrary.wiley.com/doi/10.1002/anie.201700581 |journal=Angewandte Chemie International Edition |language=en |volume=56 |issue=17 |pages=4829–4833 |doi=10.1002/anie.201700581 |issn=1433-7851|url-access=subscription }}</ref> and are useful reagents in the formation of crotyl and allyl alcohols.<ref name=":0" />
Trans-crotonaldehyde is commonly used to determine the effective Lewis acidity of Lewis acids,<ref>{{Cite journal |last=Childs |first=Ronald F. |last2=Mulholland |first2=D. Lindsay |last3=Nixon |first3=Alan |date=1982-03-15 |title=Lewis acid addticts of α,β-unsaturated carbonyl and nitrile compounds. A calorimetric study |url=https://cdnsciencepub.com/doi/10.1139/v82-118 |journal=Canadian Journal of Chemistry |language=en |volume=60 |issue=6 |pages=809–812 |doi=10.1139/v82-118 |issn=0008-4042|url-access=subscription }}</ref> determined from the change in <sup>1</sup>H NMR shift of the crotonaldehyde handle on binding to a Lewis acid. Limitations of the method include secondary interactions to the <sup>1</sup>H NMR handle obscuring the true effect of the Lewis acid, and weak donor strengths of trans-crotonaldehyde resulting in incomplete Lewis acid-base adduct formation.<ref>{{Cite journal |last=Erdmann |first=Philipp |last2=Schmitt |first2=Manuel |last3=Janus |first3=Lara |last4=Greb |first4=Lutz |date=2025-02-17 |title=Critical Evaluation of Childs Method for the NMR Spectroscopic Scaling of Effective Lewis Acidity: Limitations and Resolution of Earlier Discrepancies |url=https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202404181 |journal=Chemistry – A European Journal |language=en |volume=31 |issue=10 |doi=10.1002/chem.202404181 |issn=0947-6539|doi-access=free }}</ref>
==References== {{reflist}}
{{Functional groups}} Category:Alkenyl groups Category:Crotyl compounds