A concise and regioselective approach to the synthesis of chromenopyridine and chromenopyridinone derivatives was developed. The synthetic strategy relies on the O-propargylation of aromatic hydroxyaldehydes followed by reaction with propargylamine. The intramolecular cycloaddition reaction between the alkyne and azadiene, which is formed as an intermediate, furnished the desired skeletons.
A regioselective approach to the synthesis of benzo[h][1,6]‐naphthyridine and chromenopyrazinone derivatives was developed. The synthetic route to benzo[h][1,6]‐naphthyridines involves the N‐propargylation of aromatic aminobenzaldehydes, followed by reaction with propargylamine in the presence of DBU (1,8‐diazabicyclo[5.4.0]undec‐7‐ene). For the synthesis of chromenopyrazine and chromenopyrazinone derivatives, the acetonitrile group was introduced to salicylaldehyde derivatives, and a DBU‐promoted cyclization reaction between aldehydes and propargylamine gave the chromenopyrazines. The intramolecular heterocycloaddition reaction between the triple bond and the azadiene, which is formed as an intermediate, gave the desired structures.
Bastimolide B is a polyhydroxy macrolide isolated from marine cyanobacteria displaying antimalarial activity. It features a dense array of hydroxylated stereogenic centers with 1,5-relationships along a hydrocarbon chain. These 1,5-polyols represent a particularly challenging motif for synthesis, as the remote position of the stereocenters hampers stereocontrol. Herein, we present a strategy for 1,5-polyol stereocontrolled synthesis based on iterative boronic ester homologation with enantiopure magnesium carbenoids. By merging boronic ester homologation and transition-metal-catalyzed alkene hydroboration and diboration, the acyclic backbone of bastimolide B was rapidly assembled from readily available building blocks with full control over the remote stereocenters, enabling the total synthesis to be completed in 16 steps (LLS).
The AgOTf-catalyzed reaction of C-2 substituted pyrrole hydrazones having an N-propargyl group was studied. The selective 6-endo-dig mode of cyclization was observed, giving rise to the formation of pyrrole-fused C,N-cyclic azomethine imine derivatives. The reaction of one azomethine imine derivative with various dipolarophiles resulted in the formation of cycloadducts having a pyrazolopyrrolopyrazine skeleton. The aromaticity of C,N-cyclic azomethine imines as well as that of pyrazolopyrrolopyrazines was determined by calculating of nucleus-independent chemical shifts values.
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