The phosphonium salt from tributylphosphine and 2,6‐di(4‐methoxyphenyl)pyrylium perchlorate (3) reacted with diisopropylethylamine in acetonitrile to give 2,2′,6,6′‐tetra(4‐methoxyphenyl)‐Δ4.4′‐bi‐4H‐pyran in quantitative yield. The reaction of 3 and other 4H‐pyrylium salts with tertiary amines gave 4H‐pyrans.
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Reynolds et al. (1981) studied this question.
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