[1600-49-3] · C20H15N · Triphenylmethyl Isocyanide · (MW 269.36)
(cyanide transfer via metal-isonitrile exchange reaction2)
Alternate Names: trityl isocyanide; isocyanotriphenylmethane.
Physical Data: mp 130-133 °C (benzene).3
Solubility: insol water, cold methanol, hexane; sol common organic solvents.
Form Supplied in: white solid.
Analysis of Reagent Purity: IR n = 2130 cm-1; NMR.
Preparative Method: easily prepared in 94% yield from N-triphenylmethylformamide by dehydration with Dimethylchloromethyleneammonium Chloride (Vilsmeier reagent).4
Purification: recrystallization from benzene.
Handling, Storage, and Precautions: can be stored indefinitely at room temperature; quickly adds water in the presence of acids; easily undergoes isocyanide-nitrile rearrangement (60-80 °C in acetonitrile).5 Since some isocyanides are known to be toxic, appropriate precautions are recommended.6
Addition of organolithium reagents to triphenylmethyl isocyanide leads to the formation of unstable a-metalloaldimines which readily undergo elimination reaction to give nitriles and triphenylmethyllithium (eq 1).7 However, only when t-Butyllithium is used can the nitrile (tertiary) be isolated in high yield (88%). In all other cases, subsequent reaction of the nitrile with the organolithium reagent (used therefore in excess) gives rise to symmetrical ketones upon acid hydrolysis (eq 2). Sequential addition of t-BuLi and another organolithium reagent produces unsymmetrical (t-alkyl-alkyl) ketones in good yields (eq 3). The intermediate ketimine can also be isolated when 2 equiv of t-BuLi are used and the reaction mixture is hydrolyzed with water (eq 4).
Secondary Grignard reagents react readily with triphenylmethyl isocyanide to give secondary nitriles in 70-95% yield. Tertiary and aromatic organomagnesium compounds fail to give synthetically useful reactions. Reaction of primary Grignard reagents gives neither nitriles nor ketones as main products. When n-butylmagnesium bromide is treated with triphenylmethyl isocyanide, 5-amino-4-cyano-4-nonene is isolated in 50-60% yield (eq 5). Reaction of triphenylmethyl isocyanide with organometallic reagents can be stopped at the nitrile stage when organocopper (dialkylcuprate) reagents are used, but low yields mitigate its use as a synthetic tool.7
Triphenylmethyl isocyanide reacts readily with 2-Lithio-1,3-dithiane to give the expected nitrile in 83% yield (eq 6).8 The product can subsequently be alkylated with a variety of alkylating reagents in high yields.
Harry M. Walborsky & Marek Topolski
Florida State University, Tallahassee, FL, USA