Chroman, pyrolysis

Propionic acid, 2-bromo-3-(3-indolyl)-methyl ester rearrangement, 4, 279 Propionic acid, 3-(3,4-dimethyoxyphenyl)-dihydrocoumarin synthesis from, 3, 848 Propionic acid, indolyl-synthesis, 4, 232 Propionic acid, 3-(l-indolyl)-sodium salt pyrolysis, 4, 202 Propionic acid, 3-(3-indolyl)-intramolecular acylation, 4, 220, 221 Propionic acid, 3-phenoxy-chroman-4-one synthesis from, 3, 855 Propionic acid, 3-(3-phenylisoxazoI-5-yl)-bromination, 6, 25... 

The dehydration of chroman-2-ols, the corresponding 3-hydroxy compounds or their acetates yields chrom-2-enes. The elimination of acetic acid may be achieved by pyrolysis (62JA813, 69BSF1715, 70JOC2282), whilst loss of water is usually achieved under acidic conditions (35JCS646, 56JCS4785, 60CB1025). 

The dehydration of ds-chroman-3,4-diols with copper sulfate or p-toluenesulfonic acid gives the chroman-3-one (68BSF4203), whilst pyrolysis of the chlorohydrin (615) yields the naphthopyran-3-one (Scheme 235) (67JCS(C)1472). 

Pyrolysis of o-hydroxybenzyl alcohol at 550 °C resulted in the formation of simple o-quinone methide, which was directly observed using low-temperature IR spectroscopy.122 Pyrolysis of chroman (Scheme 33) at 400-600 °C gives the simple o-quinone methide and ethene along with o-cresol, benzofuran, and styrene.123,124 The o-quinone methide was trapped with alkenes to form Diels Adler adducts, with hydrogen gas or hydrogen atom to form o-cresol, or underwent a further pyrolysis to CO and fulvene. 

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