posted on 2013-09-06, 00:00authored byPieter Claes, Jan Jacobs, Bart Kesteleyn, Tuyen Nguyen Van, Norbert De Kimpe
2H,3′H-Spiro[benzofuran-3,2′-naphthoquinones],
constituting a new spiroheterocyclic skeleton, were synthesized starting
from 2-aryloxymethyl-1,4-naphthoquinones by means of a palladium(II)-catalyzed
reaction, which is a new spirocyclic transformation. Under optimal
conditions, i.e. 10 mol % of palladium(II) acetate, 15 mol % of 3,5-dichloropyridine,
and 5 mol % of trifluoroacetic acid in acetic acid at 110 °C,
various 2H,3′H-spiro[benzofuran-3,2′-naphthoquinones]
were synthesized in yields strongly dependent on the substitution
pattern of the aryloxy group. Unsubstituted or ortho-substituted 2-aryloxymethyl-1,4-quinones were found to rearrange
toward the corresponding 2-(4-hydroxyaryl)-1,4-quinones upon treatment
with trifluoroacetic acid.