Synthesis of Coumarins by Flash Vacuum Pyrolysis of3-(2-Hydroxyaryl)propenoic Esters, 1

Abstract

Flash vacuum pyrolysis of 3-(2-hydroxyaryl)propenoic esters gives coumarins (and other fused -pyrones) in high yield.

Racemic synthesis of 1,2-secomicrominutinin

“…On the other hand, the chemical shifts of the hydrogens on the acrylic β-carbons of these compounds were 7.80 and 7.66, respectively. Based on numerous examples from the literature, 21 we can suggest that the prepared compounds are E isomers.…”

“…This failure can be another evidence for the fact that the double bond of compound 25 has an E configuration, since it is wellknown that E isomers of 3-(2-hydroxyaryl)propenoic esters are difficult to cyclize to the corresponding coumarins by traditional methods. 21 The lability of the ketal function present in the compounds under investigation prevents the use of more drastic methods such as heating or pyrolisis.…”

Approaches to benzo[b]thiophenes by gas-phase pyrolysis of methyl 2-(alkylthio)cinnamates

“…The hydrogen atom flux is provided by the decomposition of the t-butyl radicals to 2-methylpropene. It is also known that FVP of 2-hydroxycinnamates is a good synthetic route to coumarins 14 so we propose that the thiocoumarin 9 is formed from the thiophenol 19 by an analogous mechanism (Scheme 5). The thiophenol 19 itself may be obtained directly by intramolecular decomposition of the precursor 7, or by hydrogen capture by the thiophenoxyl 15 prior to cyclisation.…”

Improved Solvent-Free Synthesis and Structure Elucidation of (E)- and (Z)-4-(Arylmethylene)-3-isochromanones

“…The maximal and minimal transmissions were between 0.992 and 0.963. Both structures were solved by direct methods in SHELXTL5 [27] and refined by full-matrix, least squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms were placed in calculated ideal positions on their respective heavy atoms.…”