This work reports new annulations of N-aryl ynamides with benzisoxazoles to form 6H-indolo[2,3-b]quinoline derivatives. The synthetic utility of this new method is manifested by its applicability to access naturally occurring alkaloids including norcryptotackeine, neocryptolepine and 11-methylneocryptol-epine. Our experimental data indicate that high-temperature conditions allow N-aryl nucleophiles to become conformationally flexible, rendering the attack at gold carbenes effective to generate reactive indoles that attack again the benzaldehyde to furnish the observed products.
This work describes gold-catalyzed
additions of vinyldiazo ketones
to N-(o-alkynylphenyl)imines to
yield 3-(furan-2-ylmethyl)-1H-indoles involving skeletal
rearrangement; these new catalytic reactions are applicable to a wide
range of substrates. We postulate a new mechanism involving an initial
addition of diazo ketones to azomethine ylide intermediates to yield
gold-containing N-alkylated indole intermediates
that undergo proton-induced 1,3-group migrations, generating azallyl
gold and allylic cation pairs.
Gold catalyzed [4+1]-annulations of 4-methoxy-1,2-dien-5-ynes with anthranils are described; the reaction mechanism involves initial formation of α-imino gold carbenes, followed by a subsequent 1,2-allene shift.
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