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Selective Partial Reduction of Various Heteroaromatic Compounds with Bridgehead Nitrogen via Birch Reduction Protocol
journal contribution
posted on 2005-03-18, 00:00 authored by Joseph T. Kim, Vladimir GevorgyanFor the first time various heteroaromatic compounds with bridgehead nitrogen, including indolizines,
bispyrrolopyrimidines, pyrroloquinolines, pyrroloisoquinolines, and bispyrrolopyrazines, were
selectively partially reduced under Birch reduction conditions. It was found that the double bond
in the fused heterocycles which possesses the highest LUMO density can be selectively reduced
under these conditions. Indolizine 6, containing an ester group at C-6, was reductively alkylated
to give dihydroindolizines 8 and 9 possessing a quaternary carbon center in good yield. It was
found that ambident substrate 12, under Birch reduction conditions, underwent smooth partial
reduction to give 4,5-dihydroquinoline 14 as a sole product with no evidence of reduction of the
side chain olefin. It was also shown that electron-rich pyrroloisoquinoline 15, which cannot be
reduced via catalytic hydrogenation conditions, was efficiently transformed into its dihydrocounterpart 16 by using the Birch reduction protocol. Finally, it was shown that various fused diazines
were smoothly and stereoselectively reduced under Birch reduction conditions to give trans-4,5-disubstituted dihydropyrimidines 30 and 32 in virtually quantitative yields.
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heteroaromatic compoundsreductively alkylateddihydroindolizines 8side chain olefindihydrocounterpart 16Indolizine 6quaternary carbon centerBridgehead NitrogenBirch reduction protocolSelective Partial Reductionester groupLUMO densityambident substrate 12Birch Reduction ProtocolBirch reduction conditionsVarious Heteroaromatic Compoundshydrogenation conditionsbridgehead nitrogen
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