Trichloromethyllithium

Li-CCl3

[2146-66-9]  · CCl3Li  · Trichloromethyllithium  · (MW 125.30)

(dichlorocyclopropanation and for nucleophilic trichloromethylation)

Physical Data: low-temperature 13C and 6Li NMR data are available,1 as are matrix IR data.2

Preparative Methods: solutions of the title compound can be obtained by treatment of Chloroform with n-Butyllithium in THF/ether/pentane (4:1:1) or ether/pentane (1:1) at -110 °C for 20 min.3 Alternatively, CCl4 or BrCCl3 may be treated with Methyllithium or n-BuLi in THF/ether/petroleum ether mixtures at -110 °C.4 The TMEDA complex with LiCCl3 can be prepared by reaction of either CHCl3 or BrCCl3 with the n-BuLi.TMEDA complex in isopentane at -108 °C.5 Deprotonation of CHCl3 with lithium dimethylamide in THF/HMPA at -105 °C does not proceed cleanly.6

Handling, Storage, and Precautions: generally stable from -110 °C to about -80 °C, depending on the solvent. There is evidence that carbenoids of this nature show greater thermal stability in THF than in ether.7 At -70 °C, solutions turn from clear to dark brown with a dark brown-black precipitate. Isolation of the decomposition products reveals what appear to be carbene-derived compounds.3b In contrast, the TMEDA complex is stable above -80 °C and decomposes to a brown-black solid material at -60 °C. When the reagent is generated in the presence of LiBr, a rapid exchange to give Li-CBrCl2 occurs.4b The reagent is probably best generated from lithium halide-free solutions of alkyllithiums.

General Considerations.

Alkyllithiums bearing halogens on the a-carbon are frequently referred to as carbenoids, reflecting a major mode of reactivity. Good general reviews of such species are available.8 At very low temperatures, however, the reagent reacts like a typical alkyllithium. The accumulated data suggest that there may be more than one isomeric form of LiCCl3. In solution a C-Li structure is present, as shown by the observation of Li-C J coupling in the 13C NMR spectrum.3a A calculational study suggests that the reagent may also exist as the rather unusual triply bridged species (1).9 It should be noted that Li-CCl3 has been studied much more intently than the analogous Li-CBr3, perhaps due to the greater thermal stability of the former. However, the reagents are not analogous in all of their reactions.

Cyclopropanations.

Formal loss of LiCl from Li-CCl3 would provide dichlorocarbene and, indeed, when alkenes are added to solutions of Li-CCl3 at around -70 °C, rapid reaction occurs resulting in dichlorocyclopropanes.3c,4b,10,11 Alkene geometry is maintained in these reactions. The situation appears to involve conversion to :CCl2 and subsequent cyclopropanation.12 The TMEDA.LiCCl3 complex is more stable in the presence of alkenes and gives dichlorocyclopropanes only slowly at -78 °C, requiring extended periods of time (eq 1).13

Similarly, reaction of Li-CCl3 with alkynes provides the dichlorocyclopropenes (3), which can be hydrolyzed to cyclopropenones (4) in overall yields of about 20% (eq 2).14

Nucleophilic Trichloromethylation.

Li-CCl3 reacts as a nucleophile within its temperature limitations. Electrophiles which require reaction temperatures higher than about -70 °C will not react well with the reagent. Yamamoto has partially solved the problem by generating the lithium reagent via deprotonation of CHCl3 with amide base in the presence of carbonyl compounds, resulting in trichlorocarbinols (eq 3).15 While this appears to be a general reaction between haloalkyllithiums and aldehydes and ketones, reactions of Li-CCl3 have only been reported with cyclohexanone and cyclopentanone. However, using CCl4/n-BuLi generating conditions, Blumbergs reported the addition of Li-CCl3 to phenyl cyclobutyl ketone and phenyl isopropyl ketone to provide adducts (5) and (6) in 44% and 54% yields, respectively.16 There is a single report of the nonselective addition of Li-CCl3 to 2-cyclopenten-1-one in low yield.17

Transformations of Trichloromethylcarbinol Adducts.

Trichloromethylcarbinols serve as intermediates in the production of 1,1-dichloroalkenes and alkynes via a b-elimination process, as well as in a homologation process via an a-elimination to produce a-chloro ketones.18 A trichloromethylcarbinol adduct (7) from an aldehyde or ketone can be converted to a methyl or a trimethylsilyl ether (8) via O-alkylation. This can be treated with n-BuLi to provide the lithium reagent (9) which undergoes Fritsch-Buttenberg-Wiechell rearrangement to (11) or it may undergo loss of RO-Li to give (10), depending on the identity of R1, R2, and R3 (eq 4). The reactivity observed appears to be linked to the sizes of the three R groups. Large alkyl groups favor the rearrangement process leading to chloro ketones. When R1 = H and R2 is not too large, dichloroalkenes and alkynes result.

Counterions Other than Li.

The analogous reagents NaCCl3 and KCCl3 have also been prepared by deprotonation of CHCl3 using the requisite metal hexamethyldisilazide.19 No significant chemical reactivity was reported.

Related Reagents.

Dibromomethyllithium; Dichloromethyllithium; Tribromomethyllithium.


1. (a) Seebach, D.; Siegel, H.; Gabriel, J.; Hassig, R. HCA 1980, 63, 2046. (b) Heinzer, J.; Oth, J. F. M.; Seebach, D. HCA 1985, 68, 1848. (c) Seebach, D.; Hassig, R.; Gabriel, J. HCA 1983, 66, 308.
2. (a) Andrews, L.; Carver, T. G. J. Phys. Chem. 1968, 72, 1743. (b) Hatzenbuhler, D. A.; Andrews, L.; Cary, F. A. JACS 1975, 97, 187.
3. (a) Kobrich, G.; Flory, K.; Drischel, W. AG(E) 1964, 3, 513. (b) Kobrich, G. AG(E) 1967, 6, 41. (c) Hoeg, D. F.; Lusk, D. I.; Crumbliss, A. L. JACS 1965, 87, 4147.
4. (a) Kobrich, G.; Flory, K.; Merkle, H. R. TL 1965, 973. (b) Miller, Jr., W. T.; Whalen, D. M. JACS 1964, 86, 2089.
5. Langer, Jr., A. W. Trans. N. Y. Acad. Sci. 1965, 27, 741.
6. Castro, B.; Villieras, J. CR(C) 1967, 264, 1609.
7. (a) Kobrich, G.; Merkle, H. R.; Trapp, H. TL 1965, 969. (b) Kobrich, G.; Merkle, H. R. CB 1966, 99, 1782. (c) Kobrich, G.; Trapp, H. CB 1966, 99, 670. (d) Kobrich, G.; Breckoff, W. E.; Heinemann, H.; Akhtar, A. JOM 1965, 3, 492.
8. (a) Siegel, H. Top. Curr. Chem. 1982, 106, 55. (b) Taylor, K. G. T 1982, 38, 2751. (c) Kobrich, G. AG(E) 1972, 11, 473. (d) ref. 3b.
9. Clark, T.; Schleyer, P.v. R. JACS 1979, 101, 7747.
10. Kobrich, G.; Flory, K.; Fischer, R. H. CB 1966, 99, 1793.
11. Kobrich, G.; Fischer, R. H. T 1968, 24, 4343.
12. Kobrich, G.; Buttner, H.; Wagner, E. AG(E) 1970, 9, 169.
13. Skell, P. S.; Cholod, M. S. JACS 1969, 91, 7131.
14. (a) Breslow, R.; Altman, L. J. JACS 1966, 88, 504. (b) Wittig, G.; Hutchinson, J. J. LA 1970, 741, 79.
15. (a) Taguchi, H.; Yamamoto, H.; Nozaki, H. JACS 1974, 96, 3010. (b) Taguchi, H.; Yamamoto, H.; Nozaki, H. BCJ 1977, 50, 1588.
16. Blumbergs, P.; LaMontagne, M. P.; Stevens, J. I. JOC 1972, 37, 1248.
17. Krebs, J.; Weber, A.; Neuenschwander, M. C 1981, 35, 55.
18. (a) Villieras, J.; Bacquet, C.; Normant, J. F. JOM 1972, 40, C1. (b) Villieras, J.; Bacquet, C.; Normant, J. F. JOM 1975, 97, 325 and 355. (c) Villieras, J.; Bacquet, C.; Normant, J. F. BSF(2) 1974, 1731.
19. Martel, B.; Hiriart, J. M. TL 1971, 2737.

Kim F. Albizati

University of California, San Diego, CA, USA



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