[98946-18-0] · C6H10Cl3NO · t-Butyl 2,2,2-Trichloroacetimidate · (MW 218.51)
Solubility: sol organic solvents, preferably nonpolar ones especially cyclohexane (polar solvents promote ionization and decomposition).
Form Supplied in: white solid; commercially available in small quantities.
Preparative Methods: 1a Potassium t-Butoxide (1.68 g, 15 mmol) was dissolved in t-butanol (30 mL) and this solution was added over 15 min to a stirred solution of Trichloroacetonitrile (21.6 g, 15 mL, 15 mmol) in dry diethyl ether (30 mL) cooled to 0 °C under nitrogen. The yellow mixture was allowed to warm to 20 °C over 1 h, and then heated to reflux for 1 h. After the reaction mixture had been cooled to rt, volatiles were removed on the rotary evaporator and the residual oil was dissolved in pentane (30 mL). The solution was filtered and the pentane was removed on the rotary evaporator. The residue was then distilled to yield 23 g (70%), bp 65-69 °C/12 mmHg, which solidified on storage.
Handling, Storage, and Precautions: the reagent is slowly hydrolyzed by water and thus should be stored cold under an inert atmosphere. The hydrolysis products are isobutene and trichloroacetamide. The use of polar solvents degrades the reagent more quickly due to decomposition in solvents that promote ionization.
The facile preparation of (1) (eq 1) provides an easily handled reagent for formation of t-butyl esters (eq 2),1a extending the usefulness of trichloroacetimidates.6 The typical previous method involved treatment of the acid with Isobutene and an inorganic acid catalyst under pressure.2 The Boron Trifluoride Etherate catalyzed reaction in cyclohexane has the advantages of Lewis acid catalysis, easy reactions on small scales, and simple workup without water or base.1,3 An instructive example is provided from the synthesis of dealanylalahopcin (eq 3).3b Yields are typically 70-90% with a simple nonaqeuous workup.
The methodology for preparing esters with reagent (1) has been extended to include ethers.1a In particular, this method has shown high selectivity for the formation of the less hindered ether (eq 4).1a Typical reactions are carried out in cyclohexane-dichloromethane mixtures for 16-20 h, giving 70% yields. Secondary alcohols require 2 equiv for effective reaction. These conditions compare favorably with the typical isobutene procedure.4
There is a single report of the very encouraging t-butylation of a nitrogen, in this case from the nonbasic hindered aniline (2) (eq 5).5
Lee H. Latimer
Sterling Winthrop, Collegeville, PA, USA