[67811-22-7]  · C3H2ClLi  · 3-Chloro-1-propynyllithium  · (MW 80.44)

(undergoes addition/substitution reactions3-5 with electrophiles; adducts with organoboranes are good sources of allenes,2 enynes,7,8 alkenes,9 and alkynes2,6)

Alternate Name: lithium chloropropargylide.

Solubility: sol ether, THF.

Form Supplied in: not commercially available; used as a solution prepared prior to reaction.

Preparative Methods: to freshly distilled Propargyl Chloride (20 mmol) in THF (10 mL) at -70 °C is added 1.6 M Methyllithium (20 mmol) in ether. The resulting clear solution is ready for use.2 Use of n-Butyllithium in place of MeLi is reported to result in lower yields in the subsequent reactions.3

Handling, Storage, and Precautions: highly moisture sensitive; use soon after preparation, in a fume hood.

Reaction with Electrophiles.

The carbenoid is used for C-C/C-X bond formation with a number of electrophiles, as shown in eqs 1-5.3-5

Synthesis of Alkylallenes.2

Trialkylboranes add to 3-chloro-1-propynyllithium in THF at -70 °C to form the adduct (1) (eq 6), which after being warmed to 25 °C can be protonated with acetic acid to give terminal alkylallenes (2) (eq 7). Where chiral, the migrating alkyl group retains its configuration.

Synthesis of a-Allenic and Homopropargylic Alcohols.6

The intermediate organoborane (1) can be treated with an aldehyde to form a C-C bond, resulting in an allenic or alkynic alcohol, depending on the temperature at which the organoborane precursor is maintained. Warming the adduct (1) to 25 °C and cooling back to -78 °C before reacting with aldehyde affords a-allenic alcohol (3) after oxidative workup (eq 8). On the other hand, if the organoborane is maintained at -78 °C or below throughout and treated with aldehyde, the resulting product, after an oxidative workup, is homopropargylic alcohol (4) (eq 9). The reaction conditions permit a wide variety of structural features in both the organoborane and aldehyde.

Synthesis of 1,5-Enynes.7

The organoborane (1) is converted to a 1,5-enyne by treating it with an allylic bromide in the presence of Copper(I) Iodide and LiOMe (eq 10).

Synthesis of Alkylallenes and 1,3-Enynes.8

As a g-halo organolithium compound, 3-chloro-1-propynyllithium has been used for C-C bond formation with organotransition metals via migratory insertion to give terminal alkylallenes or 1,3-enynes (eqs 11 and 12).

Synthesis of a,b-Unsaturated Aldehydes or Ketones.9

1,2-Dienols can be obtained by treating the title reagent with an aldehyde, followed by reduction with Lithium Aluminum Hydride. These allenols can be coupled to aryl or alkenyl halides under palladium catalysis in the presence of a tertiary amine, resulting in a facile synthesis of b-methyl-a,b-unsaturated carbonyls (eq 13).

Enones containing other carbonyl groups in the same molecule that are not accessible by the conventional aldol condensation can be synthesized using this approach.

Related Reagents.

Propargyl bromide, 3-chloro-1-butyne, and 3-chloro-3-methyl-1-butyne can also be metalated, and the derived lithium reagents, 3-bromo-1-propynyllithium, 3-chloro-1-butynyllithium, and 3-chloro-3-methyl-1-butynyllithium, can be trapped with electrophiles.10

See also Lithium Acetylide; Propynyllithium; and 3,3-Diethoxy-1-propyne.

1. Brandsma, L. Preparative Acetylene Chemistry, 2nd ed.; Elsvier: Amsterdam, 1988.
2. Leung, T.; Zweifel, G. T. JACS 1974, 96, 5620.
3. Olomucki, M.; Le Gall, J.-Y.; Barrand, I. CC 1982, 1290.
4. (a) Ref. 1, p. 82. (b) Ref. 1, p. 121. (c) Ref. 1, p. 132.
5. Picotin, G.; Miginiac, P. JOM 1987, 328, 249.
6. Zweifel, G.; Backlund, S. J.; Leung, T. JACS 1978, 100, 5561.
7. Hara, S.; Satoh, Y.; Suzuki, A. CL 1982, 1289.
8. Negishi, E.; Akiyoshi, K.; O'Connor, B.; Takagi, K.; Wu, G. JACS 1989, 111, 3089.
9. Shimizu, I.; Sugiura, T.; Tsuji, J. JOC 1985, 50, 537.
10. Battioni, J. P.; Chodkiewicz, W. BSF(2) 1969, 911.

A. V. Rama Rao

Indian Institute of Chemical Technology, Hyderabad, India

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