Synthesis of ten membered di-oxa-carbocyclic annulated flavones and olefin tethered bisflavone derivatives–olefin ring closing / cross metathesis
A practical and efficient synthetic strategy to a series of unique ten membered dioxa carbocycle annulated 6-6-10-6 tetracyclic flavones (52-58%) and oxa-olefin bridged bisflavone/chromone derivatives (50-62%) has been developed in this scheme. 3-Hydroxyflavone and C-2 styryl/heteryl chromones were synthesized and utilized as scaffolds for oxacarbocycle annulations and homocouplings at pyran ring through olefin ring-closing and cross metathesis using Grubbs’ 2nd generation catalyst. The potential application of flavones and chromone derivatives in new drug discovery discriminates the importance of powerful synthetic pathways to obtain such diverse heterocyclic derivatives.
Enantioselective synthesis of 3,4-chromanediones via asymmetric rearrangement of 3-allyloxyflavones
(Figure presented) Asymmetric scandium(III)-catalyzed rearrangement of 3-allyloxyflavones was utilized to prepare chiral, nonracemic 3,4-chromanediones in high yields and enantioselectivities. These synthetic intermediates have been further elaborated to novel heterocyclic frameworks including angular pyrazines and dihydropyrazines. The absolute configuration of rearrangement products was initially determined by a nonempirical analysis of circular dichroism (CD) using time-dependent density functional theory (TDDFT) calculations and verified by X-ray crystallography of a hydrazone derivative. Initial studies of the mechanism support an intramolecular rearrangement pathway that may proceed through a benzopyrylium intermediate.
Marie, Jean-Charles,Xiong, Yuan,Min, Geanna K.,Yeager, Adam R.,Taniguchi, Tohru,Berova, Nina,Schaus, Scott E.,Porco, John A.
supporting information; experimental part
p. 4584 - 4590
(2010/10/01)
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