Synthesis of New Hetero-Annulated Coumarins: 2,3-Dihydro-4-oxothiapyrano [2,3-<i>c</i>]-benzopyran-2-ones, 4-Oxothiapyrano[2,3-<i>c</i>]-1-benzopyran-2-ones and 2-Oxo-3,4-dihydrobenzopyrano[4,3-<i>b</i>]-4-piperidones

Abstract

2,3-Dihydro-4-oxothiapyrano[2,3-c]-1-benzopyran-2-ones 4 have been prepared by a double conjugate-addition of hydrogen sulfide to the divinyl ketone structure of 3-(1-oxoalkenyl)-1-benzopyran-2-ones 1. Subsequent oxidation of the hetero-annulated coumarins 4 with R2 = H afforded the 4-oxothiapyrano [2,3-c]-1-benzopyran-2-ones 7. 2-Oxo-3,4-dihydrobenzopyrano[4,3-b]-4-piperidones 8 were obtained by reaction of γ,δ-unsaturated β-oxoesters 2 with the N-methylimine derived from 2-hydroxybenzaldehyde. Compounds 4, 7 and 8 are the first representatives of new c-annulated coumarin ring systems.