Graduate Program
Chemistry
Degree Name
Master of Science (MS)
Semester of Degree Completion
2006
Thesis Director
Edward Treadwell
Thesis Committee Member
Daniel Sheeran
Thesis Committee Member
Mark McGuire
Thesis Committee Member
Kraig Wheeler
Abstract
Benzofuranones along with their derivatives compose a diverse array of natural products and drugs, and show a wide variety of biological effects. Several synthetic methods have been published that describe the preparation of 2-(3H)-benzofuranones having mono alkyl or aryl substituents attached to the fused furanone ring with moderate to high yields. To date, reports describing the preparation of disubstituted 2-(3H)-benzofuranones, especially with one acyl group, are rare. Early approaches are limited by low yields, economical expenditure and environmental risk.
Direct acylation of benzofuranones consistently provides O-acylated isomers rather than C-acylated isomers, which are desired products in the great majority of cases. This alkylation preference follows the "hard and soft acid and base" theory. In addition, the steric interaction and highly electronic delocalization also contributes to O-acylation greatly. When the benzofuranones are deprotonated, the fused furanone moieties are converted into aromatic furan derivatives, in which the electrons are highly delocalized. While acylation, they prefer keeping this stabilized aromatic forms, and afford O-acylated isomers. Furthermore, the geminal substituents in C-acylated isomers make the fused furanone ring crowded at the C3 position.
A facile transfer of the acyl group from the oxygen to the furanone C3 position in these kinds of compounds was developed in our lab, and provided an attractive method for the preparation of desired C-acylated products in a reliable way. Promoted by a catalytic amount of dimethylaminopyridine (DMAP), the Cacylated rearrangement products were obtained efficiently from the O-acylated isomers. It was believed that this rearrangement occurred via an active acylated pyridinium ion, which formed a supramolecular assembly with the enolate anion of 3-phenylbenzofuranone (PBF) and derivatives via T-TT stacking. It also should be noticed that those rearrangements were characterized by a dramatic color change during the process.
To investigate the scope of this C-acylation rearrangement, several PBFs with different substituents on C5 were prepared, and the transacylations were carried out. The purpose of this study was to explore how the substituents in the fused benzene ring influenced this transacylation, such as the reaction rate and the yield. Following a published method, several mono substituted 3- phenylbenzofuranones were prepared with moderate yields. Independent of the electronic-donating or electronic withdrawing ability of pendant groups, Oacylated enolates were efficiently converted into related C-acylated isomers with high yields in all cases when they were subjected to a catalytic amount of DМАР. However, their durations of deep inky blue color were longer than that of simple PBF. This suggested the reaction rate was affected by the substituent in the fused benzene ring. In addition, the yield of the arrangement with electronwithdrawing group was somewhat lower.
Recommended Citation
Zhao, Xiguang, "The study of carbon acylation of highly delocalized enolates using catalytic DMAP on 3-phenyl benzofuranone derivatives" (2006). Masters Theses. 749.
https://thekeep.eiu.edu/theses/749
