Crotyl group

A crotyl group is an organic functional group with the formula RCH₂CH=CHCH₃.¹ 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 crotylates

Crotylate (crotyl anions) can be synthesised from 2-butene (either isomer) by deprotonation with highly basic organometallic reagents,²³ typically organolithium reagents.⁴ The negative charge is delocalised over three of the carbon atoms of the crotylate group.

Crotylation reactions

Crotyl halides, crotyl alcohols,³ crotyl silanes,⁵⁶ crotonaldehyde and crotyl boronates are useful reagents for synthesizing crotyl and allyl compounds. Crotyl and allyl compounds are common intermediates in total synthesis² due to their ability to undergo sigmatropic rearrangements.

Crotylboronates are easily made from reaction of crotyl anions with alkoxy boronates,⁷⁸ and are useful reagents in the formation of crotyl and allyl alcohols.³

Trans-crotonaldehyde is commonly used to determine the effective Lewis acidity of Lewis acids,⁹ determined from the change in ¹H NMR shift of the crotonaldehyde handle on binding to a Lewis acid. Limitations of the method include secondary interactions to the ¹H 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.¹⁰

References

"crotyl". Merriam-Webster.com Dictionary. Merriam-Webster. OCLC 1032680871.
Helmboldt, Hannes; Köhler, Daniel; Hiersemann, Martin (2006-04-01). "Synthesis of the Norjatrophane Diterpene (−)-15-Acetyl-3-propionyl- 17-norcharaciol". Organic Letters. 8 (8): 1573–1576. doi:10.1021/ol060115t. ISSN 1523-7060.
Batey, Robert A.; Thadani, Avinash N.; Smil, David V. (1999-07-01). "Potassium allyl- and crotyltrifluoroborates: Stable and efficient agents for allylation and crotylation". Tetrahedron Letters. 40 (23): 4289–4292. doi:10.1016/S0040-4039(99)00774-1.
Dolgoplosk, B.A.; Beilin, S.I.; Vollershtein, E.L.; Teterina, M.P. (1975-03-25). "Studies of crotyl anion reactions and some regularities of copolymerization in hexamethylphosphortriamide". European Polymer Journal. 11 (3): 287–291. doi:10.1016/0014-3057(75)90078-6.
O'Hora, Paul S.; Incerti‐Pradillos, Celia A.; Kabeshov, Mikhail A.; Shipilovskikh, Sergei A.; Rubtsov, Aleksandr E.; Elsegood, Mark R. J.; Malkov, Andrei V. (2015-03-16). "Catalytic Asymmetric Crotylation of Aldehydes: Application in Total Synthesis of (−)‐Elisabethadione". Chemistry – A European Journal. 21 (12): 4551–4555. doi:10.1002/chem.201500176. ISSN 0947-6539.
Arefolov, Alexander; Panek, James S. (2005-04-01). "Crotylsilane Reagents in the Synthesis of Complex Polyketide Natural Products: Total Synthesis of (+)-Discodermolide". Journal of the American Chemical Society. 127 (15): 5596–5603. doi:10.1021/ja043168j. ISSN 0002-7863.
Lachance, Hugo; Lu, Xiaosong; Gravel, Michel; Hall, Dennis G. (2003-08-01). "Scandium-Catalyzed Allylboration of Aldehydes as a Practical Method for Highly Diastereo- and Enantioselective Construction of Homoallylic Alcohols". Journal of the American Chemical Society. 125 (34): 10160–10161. doi:10.1021/ja036807j. ISSN 0002-7863.
Tan, Qiuyuan; Wang, Xinqiao; Xiong, Yang; Zhao, Zimeng; Li, Lu; Tang, Pei; Zhang, Min (2017-04-18). "Chiral Amino Alcohol Accelerated and Stereocontrolled Allylboration of Iminoisatins: Highly Efficient Construction of Adjacent Quaternary Stereogenic Centers". Angewandte Chemie International Edition. 56 (17): 4829–4833. doi:10.1002/anie.201700581. ISSN 1433-7851.
Childs, Ronald F.; Mulholland, D. Lindsay; Nixon, Alan (1982-03-15). "Lewis acid addticts of α,β-unsaturated carbonyl and nitrile compounds. A calorimetric study". Canadian Journal of Chemistry. 60 (6): 809–812. doi:10.1139/v82-118. ISSN 0008-4042.
Erdmann, Philipp; Schmitt, Manuel; Janus, Lara; Greb, Lutz (2025-02-17). "Critical Evaluation of Childs Method for the NMR Spectroscopic Scaling of Effective Lewis Acidity: Limitations and Resolution of Earlier Discrepancies". Chemistry – A European Journal. 31 (10). doi:10.1002/chem.202404181. ISSN 0947-6539.

[1] "crotyl". Merriam-Webster.com Dictionary. Merriam-Webster. OCLC 1032680871.

[:1-2] Helmboldt, Hannes; Köhler, Daniel; Hiersemann, Martin (2006-04-01). "Synthesis of the Norjatrophane Diterpene (−)-15-Acetyl-3-propionyl- 17-norcharaciol". Organic Letters. 8 (8): 1573–1576. doi:10.1021/ol060115t. ISSN 1523-7060.

[:0-3] Batey, Robert A.; Thadani, Avinash N.; Smil, David V. (1999-07-01). "Potassium allyl- and crotyltrifluoroborates: Stable and efficient agents for allylation and crotylation". Tetrahedron Letters. 40 (23): 4289–4292. doi:10.1016/S0040-4039(99)00774-1.

[4] Dolgoplosk, B.A.; Beilin, S.I.; Vollershtein, E.L.; Teterina, M.P. (1975-03-25). "Studies of crotyl anion reactions and some regularities of copolymerization in hexamethylphosphortriamide". European Polymer Journal. 11 (3): 287–291. doi:10.1016/0014-3057(75)90078-6.

[5] O'Hora, Paul S.; Incerti‐Pradillos, Celia A.; Kabeshov, Mikhail A.; Shipilovskikh, Sergei A.; Rubtsov, Aleksandr E.; Elsegood, Mark R. J.; Malkov, Andrei V. (2015-03-16). "Catalytic Asymmetric Crotylation of Aldehydes: Application in Total Synthesis of (−)‐Elisabethadione". Chemistry – A European Journal. 21 (12): 4551–4555. doi:10.1002/chem.201500176. ISSN 0947-6539.

[6] Arefolov, Alexander; Panek, James S. (2005-04-01). "Crotylsilane Reagents in the Synthesis of Complex Polyketide Natural Products: Total Synthesis of (+)-Discodermolide". Journal of the American Chemical Society. 127 (15): 5596–5603. doi:10.1021/ja043168j. ISSN 0002-7863.

[7] Lachance, Hugo; Lu, Xiaosong; Gravel, Michel; Hall, Dennis G. (2003-08-01). "Scandium-Catalyzed Allylboration of Aldehydes as a Practical Method for Highly Diastereo- and Enantioselective Construction of Homoallylic Alcohols". Journal of the American Chemical Society. 125 (34): 10160–10161. doi:10.1021/ja036807j. ISSN 0002-7863.

[8] Tan, Qiuyuan; Wang, Xinqiao; Xiong, Yang; Zhao, Zimeng; Li, Lu; Tang, Pei; Zhang, Min (2017-04-18). "Chiral Amino Alcohol Accelerated and Stereocontrolled Allylboration of Iminoisatins: Highly Efficient Construction of Adjacent Quaternary Stereogenic Centers". Angewandte Chemie International Edition. 56 (17): 4829–4833. doi:10.1002/anie.201700581. ISSN 1433-7851.

[9] Childs, Ronald F.; Mulholland, D. Lindsay; Nixon, Alan (1982-03-15). "Lewis acid addticts of α,β-unsaturated carbonyl and nitrile compounds. A calorimetric study". Canadian Journal of Chemistry. 60 (6): 809–812. doi:10.1139/v82-118. ISSN 0008-4042.

[10] Erdmann, Philipp; Schmitt, Manuel; Janus, Lara; Greb, Lutz (2025-02-17). "Critical Evaluation of Childs Method for the NMR Spectroscopic Scaling of Effective Lewis Acidity: Limitations and Resolution of Earlier Discrepancies". Chemistry – A European Journal. 31 (10). doi:10.1002/chem.202404181. ISSN 0947-6539.

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