[41294-30-8]  · C5H9Br2Li  · 1,1-Dibromopentyllithium  · (MW 235.88)

(used in conjunction with n-butyllithium for homologation of carbonyl compounds1)

Solubility: sol ether, THF.

Preparative Method: prepared by the reaction of 1,1,1-tribromopentane with butyllithium in THF-ether at -100 °C.1

Handling, Storage, and Precautions: stable only at very low temperature (-100 °C); cannot be stored.

Homologation of Ketones.

1,1-Dibromo-1-pentyllithium adds readily to aldehydes or ketones. In the presence of a second equiv of n-Butyllithium, a further lithium carbenoid2,3 can be generated which undergoes a rearrangement in which a preferential migration of a hydrogen over an organic group is observed (eq 1). After hydrolysis, a mixture of two isomeric carbonyl compounds is observed (eqs 2 and 3). In some cases, only one rearrangement product is produced (eq 4)1. The reaction can be extended to other 1,1-dibromides (eq 5),1 as well as to the performance of ring expansions (eq 6).1 The related homologation of esters using Dibromomethyllithium has been extensively investigated.4

1. Villiéras, J.; Perriot, P.; Normant, J. F. S 1979, 968.
2. (a) Villiéras, J.; Bacquet, C.; Normant, J. F. JOM 1972, 40, C1. (b) JOM 1973, 97, 325. (c) Villiéras, J.; Bacquet, C.; Normant, J. F. BSF 1975, 1797. (d) Köbrich, G.; Grosser, J. TL 1972, 4117. (e) Villiéras, J.; Reliquet, A.; Normant, J. F. JOM 1978, 144, 263. (f) Villiéras, J.; Reliquet, A.; Normant, J. F. S 1978, 27.
3. (a) Villiéras, J. BSF 1967, 1511, 1520. (b) Villiéras, J.; Rambaud, M.; Tarhouni, R.; Kirschleger, B. S 1981, 68. (c) Villiéras, J.; Kirschleger, B.; Tarhouni, R.; Rambaud, M. BSF 1986, 470. (d) Villiéras, J.; Tarhouni, R.; Kirschleger, B.; Rambaud, M. BSF 1985, 825. (e) Villiéras, J.; Rambaud, M.; Kirschleger, B.; Tarhouni, R. BSF 1985, 837.
4. (a) Kowalski, C. J.; Haque, M. S. JACS 1986, 108, 1325. (b) Kowalski, C. J.; Lal, G. S. TL 1987, 28, 2463. (c) Kowalski, C. J.; Lal, G. S. JACS 1988, 110, 3693. (d) Kowalski, C. J., Reddy, R. E. JOC 1992, 57, 7194.

Paul Knochel

Philipps-Universität, Marburg, Germany

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