Abstract
An efficient synthesis of the 4(3H)-quinazolinone-based alkaloids, tryptanthrin and deoxyvasicinone has been achieved in good overall yields by using the strategy of regioselective lithiation-intramolecular electrophilic reaction as a key–step. Both the molecules have been synthesized in just two-steps from readily available starting materials.
Highlights
4(3H)-Quinazolinone is a building block for approximately 150 naturally occurring alkaloids isolated to date from a number of families of the plant kingdom, from animals, and from microorganisms
Regioselective lithiation of 6 at C-2 was achieved by using lithium diisopropylamide (LDA) which proceeded readily at -78 °C in dry THF under inert atmosphere to give a reddish solution indicating the formation of lithiated anion which subsequently reacted with the electrophile viz. methyl carboxylate in an intramolecular fashion by forming C-C bond to afford the cyclized product tryptanthrin 1 (Scheme 1)
The regioselective lithiation of 9 at C-2 was achieved by using LDA which proceeded readily at -78 °C in dry THF under inert atmosphere to form lithiated anion which subsequently reacted with the electrophile viz. methylene bromide in an intramolecular fashion by forming C-C bond to afford the cyclized product, deoxyvasicinone 2 (Scheme 2)
Summary
4(3H)-Quinazolinone is a building block for approximately 150 naturally occurring alkaloids isolated to date from a number of families of the plant kingdom, from animals, and from microorganisms. To the best of our knowledge, there is no report on regioselective lithiation of 2-unsubstituted quinazolinone at C-2 together with the subsequent reaction with an electrophile in an intramolecular fashion to afford cyclized products. The synthesis of deoxyvasicinone 2 was initiated with the formation of 3-(3-bromopropyl)quinazolin-4(3H)-one 9, obtained by alkylation of 4(3H)-quinazolinone 7 with 1,3-dibromopropane 8, and potassium carbonate in dry DMF at room temperature.
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