Triphenyl- and tetraphenyl-cyclopentadienylidene-pyrans and -thiins

Abstract
Triphenyl- and tetraphenyl-diazocyclopentadienes react with 2,6-dimethyl-4H-pyran-4-thione to form cyclopentadienylidenepyrans. A thiin has been similarly prepared from the corresponding thiinthione. The triphenyl derivative does not undergo electrophilic substitution readily. Bases do not attack these pyrans. With acids they form salts, which react with bases either to regenerate the original pyran or to produce a cyclopentadienylidenedihydropyridine.

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