Metallation and functionalization of <i>N</i>‐vinylpyrrole

Abstract

Abstract Metallation of N ‐vinylpyrrole under presumed kinetic conditions, using n ‐butyllithium in THF/hexane mixtures, n ‐butyllithium/ N,N,N′,N ′‐tetramethylethanediamine in hexane, or n ‐butyllithium/potassium tert ‐butoxide (1:1 molar ratio) in THF/hexane mixtures gives almost equal amounts of derivatives metallated at the α‐vinyl or 2‐pyrrole position. In the presence of 7–10 mol% diisopropylamine the α‐vinyl‐lithiated compound is transformed relatively slowly into the pyrrole‐lithiated derivative at ∼ +30°c. The combined use of catalytic amounts of diisopropylamine and equivalent amounts of n ‐butyllithium and potassium tert ‐butoxide gives rise to a fast and almost complete conversion into the pyrrole‐metallated derivative at temperatures in the range ‐60 to –80°c. A number of 2‐substituted N ‐vinylpyrroles have been obtained in good yields by reaction with various electrophilic reagents, in most cases preceded by the addition of anhydrous lithium bromide. N ‐Deprotection is successful only in the case of N ‐vinyl‐2‐pyrrole‐carboxaldehyde.