Efficacious Entry Into Substituted 5,6-Dihydro-4-Hydroxy-2H-Pyran-2-Ones and 2,3-Dihydro-4H-Pyran-4-Ones Utilizing Ketonic Dianions

Regioselective Synthesis of Highly Substituted Aromatic Sulfides via Carbonyl−Alkyne Exchange Reaction

“…The products were formed under very mild conditions, tolerating a wide range of functional groups. The high degree of regioselectivity observed in this reaction is in accordance with simple FMO considerations and earlier published work. , Since both dihydropyranone and α-alkynyl ketone derivatives are synthetically readily available building blocks, ,− this reaction allows the synthesis of a wide range of aromatic compounds. Nevertheless, this method showed some limitations.…”

A Convergent, Scalable Synthesis of HIV Protease Inhibitor PNU-140690

“…That the reaction is truly a saponification followed by cyclization rather than direct lactonization of the hydroxy ester is suggested by the inability of potassium tert -butoxide to mediate the closure. Use of sodium hydroxide in THF, conditions used successfully for several related substrates, resulted in unexpectedly high levels of decarboxylation to form an open-chain ketone. Use of an alcoholic medium led to improvement, but there was little difference over the series methanol−ethanol−2-propanol.…”

Natural and Synthetic 6-Aryl Pyrones. An Unexpected Reaction of Dihydropyrones with NBS Leads to the First Synthesis of Allantopyrone C

“…Many 5,6-dihydropyrones are readily available from the reaction of the dianion of ethyl acetoacetate and an aromatic aldehyde followed by base-mediated cyclization. 7 Surprisingly, there are few successful reports of the direct conversion of these compounds into the corresponding pyrones. A report by Soldi describes the failure of DDQ, CAN, IBX and manganese dioxide to oxidize 5,6-dihydro-4-methoxy-6-vinylpyrone.…”

“…8 Dihydropyrone 6 was synthesized from benzaldehyde and the dianion of ethyl acetoacetate followed by O-methylation. 7 Attempts to oxidize 6 using DDQ, trityl tetrafluoborate, or elemental sulfur returned recovered starting material. 9 Reactions employed to cleave benzyl esters (DDQ, MeOH) also returned starting material.…”