Lithium Phenylthio(2-vinylcyclopropyl)cuprate1

[61754-34-5]  · C11H12CuLiS  · Lithium Phenylthio(2-vinylcyclopropyl)cuprate  · (MW 246.79) (cis)

[71647-04-6] (trans)


(heterocuprate useful in 1,4-addition-elimination reactions2 and annulations3)

Solubility: sol THF; less sol ether.

Analysis of Reagent Purity: an assay to determine relative thermal stabilities4 can be used to estimate reagent quality and concentration: a sample of known volume and temperature is quenched with excess PhCOCl; the yield of 2-vinylcyclopropyl phenyl ketone is measured by GC or HPLC, the response of which is calibrated using authentic product and an appropriate internal standard.

Preparative Method: 2-vinylcyclopropyllithium5 is prepared by cooling a 0.25 M ether or THF solution of 1-bromo-2-vinylcyclopropane6 under Ar to -78 °C. Dropwise addition of 1.1-1.4 equiv of a solution of t-Butyllithium is followed by stirring for 2 h. One equiv of Phenylthiocopper(I)7 is added, and the resultant slurry is diluted with 5 mL THF per mmol of cyclopropane. The reaction is warmed to -20 °C; a clear, light brown solution of cuprate forms after stirring for 20 min. It is cooled to -78 °C and is used directly.

Handling, Storage, and Precautions: best results are obtained with PhSCu prepared from high purity CuI salts,8 dry, O2-free solvents, and alkyllithium solutions free of contaminating alkoxides or hydroxides.9 t-BuLi is pyrophoric;10 care must be exercised in its handling. Use in a fume hood.

This cyclopropyl organometallic reagent is representative of the heterocuprate class of organocopper reagents.11 Only the cyclopropyl group, and not the SPh group, is nucleophilically reactive. The nontransferable SPh group, or dummy ligand,12 provides enhanced thermal stability and solubility compared to the analogous homocuprate. Heterocuprates generally exhibit less nucleophilic reactivity than the corresponding homocuprates; however, increased thermal stabilities coupled with greater efficiency in use of the transferable ligand make them reasonable alternative reagents. This is particularly true when higher reaction temperatures are required, or when the organolithium used to form the cuprate is difficult or expensive to prepare.

Lithium phenylthio(2-vinylcyclopropyl)cuprate has been used in acylations3 and 1,4-addition-elimination reactions with 3-halo-2-alkenones.13 The products of these reactions undergo high-yield thermal ring expansions (see Lithium Cyclopropyl(phenylthio)cuprate), providing a two-step, seven-membered ring annulation method. 4-Cycloheptenones and various seven-membered ring bicycloalkadienones and spiroalkadienones (eq 1)13 can be prepared.

Either the cis- or trans-isomer or a mixture of isomeric 1-bromo-2-vinylcyclopropanes can be used in the reaction, although rearrangement is more facile with the cis-isomer. The method has been used in a convergent total synthesis of the sesquiterpene b-himachalene to assemble the 7,6-fused ring core of the natural product.14

Related Reagents.

Lithium Bis(2-vinylcyclopropyl)cuprate; Lithium Dimethylcuprate; Lithium Methyl(phenylthio)cuprate.

1. (a) Lipshutz, B. H.; Sengupta, S. OR 1992, 41, 135. (b) Posner, G. H. An Introduction to Synthesis Using Organocopper Reagents; Wiley: New York, 1980.
2. (a) Perlmutter, P. Conjugate Addition Reactions in Organic Synthesis; Pergamon: New York, 1992. (b) Kozlowski, J. A. COS 1991, 4, 169. (c) Hulce, M.; Chapdelaine, M. J. COS 1991, 4, 237. (d) Chapdelaine, M. J.; Hulce, M. OR 1990, 38, 225. (e) Posner, G. H. OR 1975, 22, 253. (f) Posner, G. H. OR 1972, 19, 1.
3. Piers, E.; Burmeister, M. S.; Reissig, H.-U. CJC 1986, 64, 180.
4. Bertz, S. H.; Dabbagh, G. CC 1982, 1030.
5. Wender, P. A.; Filosa, M. P. JOC 1976, 21, 3490.
6. (a) Landgrebe, J. A.; Becker, L. W. JOC 1968, 33, 1173. (b) Seyferth, D.; Yamazaki, H.; Alleston, D. L. JOC 1963, 28, 703.
7. PhSCu in purities of 95 to >98% is commercially available. For the preparation of PhSCu in THF, see Corey, E. J.; Boger, D. L. TL 1978, 39, 4597.
8. Purification methods: (a) Posner, G. H.; Sterling, J. J. JACS 1973, 95, 3076. (b) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals, 3rd ed.; Pergamon: New York, 1988; p 322. (c) Lipshutz, B. H.; Whitney, S.; Kozlowski, J. A.; Breneman, C. M. TL 1986, 27, 4273.
9. Corey, E. J.; Naef, R.; Hannon, F. J. JACS 1986, 108, 7114.
10. Wakefield, B. J. Organolithium Methods; Academic: New York, 1988; pp 11-15.
11. Posner, G. H.; Whitten, C. E.; Sterling, J. J. JACS 1973, 95, 7788.
12. Lipshutz, B. H. SL 1990, 119.
13. Piers, E.; Morton, H. E.; Nagakura, I.; Thies, R. W. CJC 1983, 61, 1226.
14. Piers, E.; Ruediger, E. H. CJC 1983, 61, 1239.

Martin Hulce

Creighton University, Omaha, NE, USA

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