Reactions of ortho-quinones with ethoxycarbonylmethylene(triphenyl)-phosphorane. Trapping of the ortho-quinone methanide intermediates

Abstract

The reactions of the ortho-quinones (5a-d) with the phosphorus ylide (6) afforded, besides the expected coumarin derivatives ( l o a d ) , compounds (9d), ( l l b and c), (13), and (14). When the reactions between compounds (5a-d) and (6) were carried out in the presence of ethyl vinyl ether (20) the pyran derivatives (21a, b, and d) and (22a, b, and d) were obtained as main products, by a [4 + 21 trapping process of the ortho-quinone methanide intermediates (7a, b, and d) with the dienophile (20). Similarly, the reaction between compounds (5a) and (6) in the presence of a-methylstyrene afforded mainly the pyrans (23 I and 11). Compounds (16), (19), and (24) were also prepared and studied.

Antioxidants and Inflammatory Disease: Synthetic and Natural Antioxidants with Anti-Inflammatory Activity

“…Fylaktakidou and co-workers [72] reported the synthesis and evaluation of fused 1,3-dioxolocoumarins as antioxidants and anti-inflammatory agents. These compounds were synthesized according to Scheme 3 and 4 in connection to their previous work on the synthesis of coumarin derivatives [73][74][75][76][77][78][79]69] and based on their recent studies on the synthesis and biological activities of 4-substituted coumarins with a heterocyclic ring [69][70][71][72]80], which were found to possess significant antiinflammatory and antioxidant activities, as well as inhibition of soybean lipoxygenase.…”

Synthesis and biological evaluation of new benzo[f]furo[2,3‐h]‐and benzo[f]pyrano[2,3‐h]coumarin derivatives.

“…The reaction mixtures in both methods were separated by column chromatography. From the reaction of 1 with o-quinone 2 only ethyl 2-isopropenyl-2-methyl-5-oxo-2,3-dihydro-5H-benzo[f]-furo [2,3- The formation of coumarins 3, 5, 7 can be explained by the known [16,17] mechanism depicted in Scheme 2. Wittig monoolefination of the o-quinone used with ylide 1 gives the o-quinonemethide intermediate 8, which by further Michael addition of a second ylide species 1 affords the betaine 9.…”

“…For the reactions two methods were used. According to the first method (A), used earlier by our group for analogous reactions [16][17][18], a solution of the easy prepared [19] o-quinone 2, 4, 6 and excess of the ylide 1 (2.2 equivalents) was refluxed in dry dichloromethane (DCM) for 3-6 hours. In the second method (B) a mixture of o-quinone and the ylide in dry toluene was heated in a commercial microwave oven (800 W) for 3 min.…”

A Catalyst‐Controlled Aerobic Coupling of ortho‐Quinones and Phenols Applied to the Synthesis of Aryl Ethers

“…As the two carbonyl groups in 5 are electronically differentiated, deoxyfluorination, [31] Wittig olefination, [32] and nucleophilic addition [33] occur selectively at the more electrophilic carbon atom, directly elaborating 5 into ortho-fluorophenol 7, coumarin 9,o ra-epoxy ketone 8.A lternatively,c leavage of the diketone with lead tetraacetate in methanol [34] provides muconic ester 6 as as ingle geometric isomer, which underscores the diversity of aryl ethers that can be accessed from asingle ortho-quinone precursor. As the two carbonyl groups in 5 are electronically differentiated, deoxyfluorination, [31] Wittig olefination, [32] and nucleophilic addition [33] occur selectively at the more electrophilic carbon atom, directly elaborating 5 into ortho-fluorophenol 7, coumarin 9,o ra-epoxy ketone 8.A lternatively,c leavage of the diketone with lead tetraacetate in methanol [34] provides muconic ester 6 as as ingle geometric isomer, which underscores the diversity of aryl ethers that can be accessed from asingle ortho-quinone precursor.…”

“…Thedecagram synthesis and diversification of 5 highlights the versatility of ortho-quinones (Scheme 3A). As the two carbonyl groups in 5 are electronically differentiated, deoxyfluorination, [31] Wittig olefination, [32] and nucleophilic addition [33] occur selectively at the more electrophilic carbon atom, directly elaborating 5 into ortho-fluorophenol 7, coumarin 9,o ra-epoxy ketone 8.A lternatively,c leavage of the diketone with lead tetraacetate in methanol [34] provides muconic ester 6 as as ingle geometric isomer, which underscores the diversity of aryl ethers that can be accessed from asingle ortho-quinone precursor.…”