Some mercuration reactions of substituted pyrroles

Abstract

Mercuration of N-unsubstituted pyrroles with mercury(I1) acetate results in immediate precipitation of the N-mercurated derivative, which is insoluble in virtually all organic solvents. If the pyrrole N atom is protected (e.g. with Me, CH20CH2Ph, or C02t-Bu) then mercuration takes place efficiently at unsubstituted pyrrole carbons. Subsequent palladium/olefin (Heck-type) reactions afford the corresponding pyrrole acrylate when, for example, the olefin is methyl acrylate; deprotection (when the N-substituent is CH20CH2Ph or C02t-Bu) then affords the required carbon-substituted pyrrole. Attempts to deprotect the N-methylpyrroles were unsuccessful.

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…For N-H pyrroles, mercuration with mercury(II) acetate leads to N-mercuration, while various N-substituted pyrroles are mercurated at C2 or C3. Such C-mercurated pyrroles undergo Heck-type reactions with alkenes [405].…”

Palladium‐Catalysed Cross‐Coupling and Related Reactions Involving Pyrroles

“…In a similar vein, Smith’s group reported that C3‐unsubstituted pyrroles are readily converted into the corresponding C3‐mercurated derivatives upon reaction with Hg(OAc) 2 . Treatment of such derivatives with LiPdCl 3 and methyl acrylate then affords – presumably via trans ‐metallation then a Heck reaction – the expected β‐substituted acrylate 47. Monti and Sleiter have described related processes involving C3‐thallated pyrroles 48…”

Metallation of N-vinylpyrroles and -indoles with Hg(OAc)2: N-vinyl vs. pyrrole nucleophilic sites

“…12 In light of the easy mercuration of pyrroles (even in aqueous media 10 ), of certain interest are the cross-coupling reactions of the N-protected mercurated pyrroles (e.g., pyrrolyl mercuric acetate) with functional olefins to afford the corresponding functionalized C-vinylpyrroles. 13 Since recently, N-vinylpyrroles and -indoles with diverse substituents have become readily available via the direct reactions of ketones (in the form of their ketoximes) with acetylene in the superbasic KOH/DMSO suspensions (Trofimov reaction). 14 This new large group of reactive pyrroles and indoles proved to be rewarding building blocks and monomers for the design of optoelectronic materials 15 and pharmaceuticals.…”