Palladium-Catalyzed Construction of Polycyclic Heterocycles by an Alkyne Insertion and Direct Arylation Cascade

Abstract

Cascade cyclization of bromoenynes bearing an aryl group with catalytic amounts of palladium(II) acetate and cesium carbonate led to the direct construction of tri- or tetracyclic heterocycles. Direct arylation of a pyrrole, furan or thiophene ring in the cascade reaction affords the corresponding fused heteroarenes in moderate to good yields.

Key words

tandem reaction - palladium - polycycles - fused-ring systems - ring closure

References

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11

For example, the reaction of 11b with Pd(OAc)₂ (2 mol%) using K₂CO₃ (2 equiv) as the base stereoselectively gave the monocyclic product 13b in 94% yield (Scheme  [4] ).

Scheme 4

12

A similar result was obtained with malonate congener 19c, which produced diyne 21 in 69% yield (Scheme  [5] ).

Scheme 5