Stereoselective cascade double-annulations provide diversely ring-fused tetracyclic benzopyrones.


Baskar B, Wittstein K, Sankar MG, Khedkar V, Schürmann M, Kumar K.

Org Lett. 2012 Dec 7;14(23):5924-7. doi: 10.1021/ol3028412. Epub 2012 Nov 14.

A cascade double-annulation strategy employing diverse pairs of zwitterions with 3-formylchromones is presented that provides stereoselective access to complex tetracyclic benzopyrones. Different zwitterions incorporated different rings that include aza-, oxa-, and carbocycles fused to a common benzopyrone scaffold and in the process created three contiguous chiral centers including an all-carbon-quaternary center with high efficiency and excellent stereoselectivity.

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