Abstract
Pyrylium Compounds. 30. C‐Alkylation of 1,3,5‐Triaryl‐pentene‐1,5‐dione Enolates: A Simple Approach to 3‐Alkylsubstituted 2,4,6‐Triarylpyrylium Salts1,3,5‐Triaryl‐pentene‐1,5‐dione enolates (10), obtainable in crystalline form from 2,4,6‐triarylpyrylium pseudobases (9) and sodium methoxide in benzene/ether, react in dipolar aprotonic solvents (e.g. DMSO, DMF) with various types of alkyl iodides to give C‐alkylation products (11) which afford 3‐substituted 2,4,6‐triarylpyrylium salts (12) on treatment with perchloric acid. This reaction sequence proved to be a convenient synthetic route to pyrylium salts (12) having 3‐oriented substituents such as normal or branched alkyl groups CnH2n+1 (e.g.n = 1–5), isotopically modified alkyl groups (e.g. C[2H3], C2[2H5]), allyl type substituents (e.g. CH2CHCH2, MeCHCHCH2, CH2, CH2CMeCH2) or benzyl groups (e. g. PhCH2, 4‐BrC6H4CH2). Bifunctional alkylating agents (e.g. 1,4‐diiodobutane, o‐xylylenediiodide) resulted in a novel type of bispyrylium salts (14) with 3,3′‐linkage. The pyrylium salts obtained were characterized by their 1H‐n.m.r. and u.v. spectra as well as, in most cases, by transformation into the corresponding pyridine derivatives (13) and bispyridines (15) respectively.
Published Version
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