[-] · C4H6Li2O · Lithium 2-Lithiomethyl-2-propenolate · (MW 83.98)
(nucleophilic reagent for the generation of functionalized isoprenoid compounds through alkylation or addition reactions)
Physical Data: gold colored solid.
Solubility: insol hexane.
Preparative Methods: metalation of methallyl alcohol with n-Butyllithium-Potassium t-Butoxide.
Handling, Storage, and Precautions: air, water, and temperature (greater than 0 °C) sensitive.
The allylic dianion is prepared by the action of t-BuOK/n-BuLi (i.e. Schlosser's base) in hexane on methallyl alcohol.1 The active reagent is formed immediately upon the completion of the alcohol addition (0 °C). The yield of allylic anion formed appears to be extremely sensitive to reaction conditions (e.g. fresh n-BuLi,1 solvent2).
The methallyl alcohol dianion can be alkylated with alkyl halides (eq 1)3 or epoxides (eq 2),4 silylated (eq 3),2,5 or undergo addition reactions with aldehydes or ketones (eq 4).1 This carbon-carbon bond-forming process introduces a functionalized isoprenoid unit.
A similar transformation is observed with 2-ethylallyl alcohol derived from commercially available 2-ethylacrolein (eq 5). The observed addition products are mixtures of 1,4-diols derived from attack on both the primary and secondary carbons. Oxidation with activated Manganese Dioxide gives the a-methylene- and (Z)-a-ethylidenebutyrolactones (eq 5).6 See also Methallyllithium.
Robert M. Carlson
University of Minnesota, Duluth, MN, USA