Cyclization of 4-Phenoxy-2-coumarins and 2-Pyrones via a Double C–H Activation
作者:Katrina Mackey、Leticia M. Pardo、Aisling M. Prendergast、Marie-T. Nolan、Lorraine M. Bateman、Gerard P. McGlacken
DOI:10.1021/acs.orglett.6b00751
日期:2016.6.3
Aryl–heteroaryl coupling via double C–H activation is a powerful transformation that avoids the installation of activating groups. A double C–H activation of privileged biological scaffolds, 2-coumarins and 2-pyrones, is reported. Despite the rich chemistry of these molecular frameworks, the yields are very good. Excellent regioselectivity was achieved on the pyrones. This methodology was applied to the synthesis
Intramolecular Direct Arylation of 3-Halo-2-pyrones and 2-Coumarins
作者:Marie-T. Nolan、Leticia M. Pardo、Aisling M. Prendergast、Gerard P. McGlacken
DOI:10.1021/acs.joc.5b02027
日期:2015.11.6
worked well. The methodology was extended to 2-coumarins and applied to the synthesis of flemichapparin C and a novel analogue. Deuteriumisotope effects, typical of a concerted metalation-deprotonation (CMD) mechanism, were observed in the case of a bromopyrone, but a highly unusual, inverse kinetic isotopeeffect was evident using a chlorocoumarin, implying that a different mechanism is operating.
Laccase-catalyzed domino reactions of 4-hydroxy-6-methyl-2H-pyran-2-one or substituted 4-hydroxy-2H-chromen-2-ones with catechols using molecular oxygen as an oxidant afford coumestans and related O-heterocycles with yields ranging from 51% to 99%.
A copper-catalyzed intramolecular cross dehydrogenative C–O coupling reaction of 2′-hydroxyl-3-arylcoumarins was developed. This protocol provided a facile and efficient strategy for the construction of natural coumestans and derivatives in moderate to high yields. This transformation exhibited good functional group compatibility and was amenable to substrates with free phenolic hydroxyl groups.
Syntheses of pterocarpenes and coumestans via regioselective cyclodehydration
作者:Maloy Nayak、Youngeun Jung、Ikyon Kim
DOI:10.1039/c6ob01451h
日期:——
pterocarpenes and coumestans is described. BCl3-mediated dehydrative cyclization of 1,3-diaryloxyacetones under mild conditions permitted regioselective ring closure to afford 3-((2-iodoaryloxy)methyl)benzofurans which were converted to the corresponding pterocarpenes by Pd-catalyzed intramoleculardirectarylation. The subsequent benzylic oxidation led to coumestans. This sequence was applied to the formal