(R1 = R2 = H) (allyl)

[690-19-7]  · C3H5F3Si  · Allyltrifluorosilane  · (MW 126.15) (R1 = Me, R2 = H) (Z-crotyl)

[51676-18-74]  · C4H7F3Si  · Crotyltrifluorosilane  · (MW 140.18) (R2 = Me, R2 = H) (E-crotyl)

[114067-35-5] (R1 = R2 = Me) (Me-crotyl)

[114067-34-4]  · C5H9F3Si  · (Methylcrotyl)trifluorosilane  · (MW 154.21)

(highly regioselective and stereoselective allylation and crotylation reagent, usually activated by fluoride ions or hydroxy compounds1a)

Physical Data: (Z)-crotyl: bp 52 °C; Me-crotyl: bp 71 °C.

Solubility: sol common organic solvents.

Analysis of Reagent Purity: 1H NMR.

Purification: by distillation.

Preparative Methods: allyltrifluorosilanes are most conveniently prepared by the reaction of the corresponding trichlorosilanes with SbF32 or ZnF2.4H2O.3 Stereohomogeneous (E)- and (Z)-crotyltrifluorosilanes are prepared as shown in eqs 1 and 2.4

Handling, Storage, and Precautions: the reagents can be stored in a glass bottle but must be protected from moisture. Use in a fume hood.

Fluoride Ion-Mediated Allylation of Aldehydes.

Allyltrifluorosilanes undergo regiospecific and stereospecific allylation reactions with a variety of aldehydes. Thus in the presence of an excess amount of Cesium Fluoride, allyltrifluorosilanes form pentacoordinate tetrafluorosilicates which undergo the allylation reaction with aldehydes, presumably through a six-membered transition state. The regio- and stereochemistry of the products are consistent with this postulate (eq 3).

Hydroxy Compound-Mediated Allylation.

Allylation reactions of aldehydes with allyltrifluorosilanes can also be effected in the presence of a wide variety of hydroxy compounds and Triethylamine to give the corresponding homoallyl alcohols in a regio- and stereospecific manner.5 Typically in the case with catechol, allyldifluorosilicon catecholate is proposed to be the intermediate (eqs 4 and 5). No rigorous drying of the reaction system is necessary. Interestingly, this reagent system can discriminate linear from a-branched alkanals. The structure-reactivity relationships in pentacoordinate allylsilicates are explained in terms of the Lewis acidity of the silicon centers.

Allylation of a-Hydroxy Ketones.

Allyltrifluorosilanes react with a-hydroxy ketones, without protection of the hydroxy group, in the presence of triethylamine to yield tertiary homoallyl alcohols with extremely high regio- and diastereospecificity (eqs 6 and 7).6

Crotylation of Aldimines.

Aliphatic and aromatic aldimines are crotylated in a selective manner by the reaction with (E)- and (Z)-crotyltrifluorosilanes in the presence of CsF (eq 8).

Related Reagents.

B-Allyldiisocaranylborane; B-Crotyldiisopinocampheylborane; Crotyldimethoxyborane; Crotyltrichlorosilane; Diisopropyl 2-Allyl-1,3,2-dioxaborolane-4,5-dicarboxylate.

1. (a) Sakurai, H. SL 1989, 1. (b) Sakurai, H. Selectivities in Lewis Acid Promoted Reactions; Schinzer, D., Ed.; NATO ASI Series, 1988; Chapter 11. (c) Sakurai, H. Chemistry and Technology of Silicon and Tin; Kumar Das, V. G.; Weng, N. S.; Gielen, M., Eds.; Oxford: OUP, 1992; Chapter 3. (d) Fieser, M.; Fieser, L. F. FF 1975, 5, 617; 1979, 7, 396.
2. &RRbreve;e&rbreve;icha, R.; &CCbreve;apka, M. CCC 1974, 39, 144.
3. Kira, M.; Kobayashi, M.; Sakurai, H. TL 1987, 28, 4081.
4. Kira, M.; Hino, T.; Sakurai, H. TL 1989, 30, 1099.
5. Kira, M.; Sato, K.; Sakurai, H. JACS 1990, 112, 257.
6. Sato, K.; Kira, M.; Sakurai, H. JACS 1989, 111, 6429.

Hideki Sakurai

Tohoku University, Sendai, Japan

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