Reported herein is a Rh-catalyzed redox-neutral annulation of primary benzamides with diazo compounds, representing an efficient and economic protocol to isoquinolinones. The procedure exhibited good functional group tolerability, scalability, and regioselectivity, obviating the need for oxidants, and only environmentally benign N2 and H2O were released. Further utilization of the method provided an alternative route to functionalized isoquinolines.
AR h III -catalyzed tandem C À Ha ctivation and C À Nb ond formation reaction between oximes and diazo compounds for the synthesiso fh eterocycle-fused pyridine N-oxides hasb een developed. Ther eaction exhibitsg ood functional group tolerance andr egioselectivity.A fter simple transformation, the 1-substituted, 1,3-disubstituted, 1,4-disubstituted and 1,3,4-trisubstituted heterocycle-fused pyridineswere all obtained in high efficiency.Moreover,t his strategyh as also been expanded to the synthesis of ak ey intermediate for the construction of one potential anti-HIV agent.Keywords: C À Ha ctivation;d iazo compounds;h eterocycle-fused pyridine N-oxides;o ximes;R h III -catalysis Pyridine N-oxidesa nd their derivatives constitute ac ore skeleton of various natural products, [1] pharmaceutical agents, [2] ligands [3] andf unctional organic materials.[4] Methods for the rapid access to andfunctionalization of these compoundsh ave attracted continuous synthetic interest. Oxidationo fp yridinesi so ne of the most frequentw ays at the earlys tage,e ven thought he pre-synthesis of pyridines and the risk of over-oxidation of some sensitive groups could restrict the substrate scope and diversity (Scheme 1, a).[5] Recently,s ignificant progress has been madei nm any protocols for constructing pyridine N-oxides employing transition-metal catalysis.[6] Gold-or silver-catalyzed intramolecular electrophilic cyclizations of oximes offering isoquinoline N-oxidesh aveb eend escribedb yS hin (Scheme 1, b); [7] however, the oximes are prepared from halogenated aromatic ketones or aldehydesw ith terminal alkynes in several steps,a nd only 3-substitutedo r1 ,3-disubstituted productsc ould be achieved. To address these shortcomings,n ickel [8] -, rhodium [9] -, or palladium [10] -catalyzed intermolecular annulations between oximes and internal alkynes affording 3,4-disubstituted or 1,3,4-trisubstituted isoquinoline N-oxidesh aveb eene xplored (Scheme 1, c). Them ajor limitation of these reactions was the Scheme1.Synthesis of compounds containing pyridine Noxides.
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