[3052-45-7] · C3H5Li · Isopropenyllithium · (MW 48.02)
(terpenoid synthesis; precursor of isopropenyl metals2)
Alternate Name: 2-lithiopropene.
Physical Data: 1H NMR data have been reported.5a
Preparative Methods: can be prepared in ethereal solution by reaction of Lithium powder (containing 2% of Na) with isopropenyl chloride or bromide (eq 1)4 or by transmetalation between an organolithium and isopropenyltrialkyltin (eq 2).5
Related reagents can be prepared by reaction of n-Butyllithium with an arenesulfonyl hydrazone (eq 3)6 and by the metal-halogen exchange reaction7 between vinyl bromides or iodides and t-Butyllithium (eq 4).
Handling, Storage, and Precautions: the solution of isopropenyllithium in diethyl ether must be handled with care since it is flammable and may ignite on contact with moisture and air. It should be stored and handled in an inert atmosphere (argon) and measured or transferred by means of a hypodermic syringe or cannula. The solution may deteriorate with time and the concentration of the reagent should be measured by titration3 before use.
Isopropenyllithium reacts with various electrophiles,1-7 for example, aldehydes (eq 5),7 ketones,8 alkyl halides (eq 6),4 amides (eq 7),9 and epoxides (eq 8).10
The conjugate addition of isopropenyllithium to a,b-enones can be accomplished by using 2 equiv of MAD (Methylaluminum Bis(2,6-di-t-butyl-4-methylphenoxide)) (eq 9).11
Isopropenyllithium reacts with trialkylboranes and tetraphenylphosphonium bromide (eqs 10 and 11).12,13
The corresponding cuprates,2 obtained by transmetalation between copper salts and isopropenyllithium (see Lithium Diisopropenylcuprate), react with alkyl halides (eq 12)14 and a,b-enones in a 1,4-fashion (eq 13).15
The organocerium reagent, prepared from isopropenyllithium and anhydrous Cerium(III) Chloride, reacts cleanly with easily enolizable ketones to afford the addition products in good yield (eq 14).16
a-Substituted vinyllithium reagents7a,17 have been described. 4-Chloro-2-lithio-1-butene, readily prepared by transmetalation from the tin derivative, reacts smoothly with aldehydes or ketones (eq 15).5b
The reaction of an a-substituted vinyllithium with copper salts leads to an a-substituted vinylcuprate which reacts easily with an allyl bromide (eq 16).18
Gérard Linstrumelle & Mouâd Alami
Ecole Normale Supérieure, Paris, France