Solubility: prepared as a solution in ether; presumably can also be prepared in THF.
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 phenyl ketone is measured by GC, the response of which is calibrated using authentic product and n-dodecane as internal standard.
Handling, Storage, and Precautions: best results are obtained with high purity copper(I) salts,9 dry, oxygen-free solvents, and alkyllithium solutions free of contaminating alkoxides or hydroxides.10 n-BuLi is used to prepare the intermediate reagents lithium thiophenoxide and 3,3-diethoxy-2-lithiopropene, and is pyrophoric;11 due care must be exercised in its handling. Thermal decomposition occurs at &egt;-40 °C. Use in a fume hood.
This vinylic organometallic reagent is representative of the heterocuprate class of organocopper reagents. The vinylic group is reactive as a nucleophile, whereas the SPh group is not. Such nontransferable groups are called dummy ligands;12 the SPh dummy ligand in particular is typically found to provide 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 relatively high reaction temperatures are required, or when the organolithium used to form the cuprate is difficult or expensive to prepare.
1,4-Adduct (1) has been used to prepare a-methylene-d-valerolactones (eq 3),5 common structural motifs in marine cembranolides.3a If a 4-trimethylsilyloxy- or 4-t-butyldimethylsilyloxy-2-cycloalkenone is used as substrate for the 1,4-addition, trans-a-methylene-g-butyrolactones can be prepared;14 this strategy utilizes the steric control effect of the 4-silyloxy substituent, which causes the nucleophile to attack at the opposing face of the double bond.
Although the phenylthiocuprate is reported to be unreactive with cyclohexene epoxide, the homocuprate Lithium Bis(3,3-diethoxy-1-propen-2-yl)cuprate and mixed homocuprate lithium (3,3-diethoxy-1-propen-2-yl)(3,3-dimethyl-1-butynyl)cuprate undergo both 1,2- and 1,4-additions to cycloalkadiene monoepoxides (eq 4).15 1,4-Addition is distinctly favored when diethyl ether is used as solvent. The hydroxyacetal adducts can be used in the stereospecific construction of a-methylene-g-butyrolactones of 1,3-diols. For example, when (2) is isolated from (3) by vacuum distillation, transacetalization affords a cyclic mixed acetal. Upon oxidation with Jones reagent, the corresponding trans-a-methylene-g-butyrolactone is isolated (eq 5). If 1,4-adduct (3) is hydrolyzed, the resultant aldehyde can be oxidized to its corresponding acid; iodolactonization provides a cis-a-methylene-g-butyrolactone (eq 6).
3,3-Diethoxy-1-propen-2-ylcopper; Lithium Bis(3,3-diethoxy-1-propen-2-yl)cuprate; and Lithium (3,3-Diethoxy-1-propen-2-yl)(3,3-dimethyl-1-butynyl)cuprate; for related heterocuprates, see Lithium Methyl(phenylthio)cuprate; for discussion of lithium dialkylcuprates, see Lithium Dimethylcuprate.
3. For a recent review: Petragnani, N.; Ferraz, H. M. C.; Silva, G. V. J. S 1986, 157. As components in total syntheses of natural products: (a) Marshall, J. A. In Studies in Natural Products Chemistry; Rahman, A.-u., Ed.; Elsevier: New York, 1992; Vol. 10, p 3. (b) McMurray, J. E.; Dushin, R. G. In Studies in Natural Products Chemistry; Rahman, A.-u., Ed.; Elsevier: New York, 1991; Vol. 8, p 15.
5. Grieco, P. A.; Wang, C.-L. W.; Majetich, G. JOC 1976, 41, 726.
6. Claisen, L. CB 1898, 31, 1015.
7. Ficini, J.; Depezay, J.-C. TL 1969, 4797.
8. (a) For preparation of PhSCu in THF, see Corey, E. J.; Boger, D. L. TL 1978, 4597. (b) PhSCu in purities of 95->98% is commercially available.
9. 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.
11. Wakefield, B. J. Organolithium Methods; Academic: New York, 1988; pp 11-15.
13. Marino, J. P.; Floyd, D. M. TL 1975, 3897.
14. Boeckman, R. K. Jr.; Ramaiah, M. JOC 1977, 42, 1581.
15. Marino, J. P.; Farina, J. S. JOC 1976, 41, 3213.
16. (a) Baillargeon, V. P.; Stille, J. K. JACS 1986, 108, 452. (b) Schoenberg, A.; Heck, R. F. JACS 1974, 96, 7761.
17. Mahoney, W. S.; Brestensky, D. M.; Stryker, J. M. JACS 1988, 110, 291.