Electrooxidative tricyclic 6-7-6 fused-system domino assembly to allocolchicines by a removable radical strategy.

Natural allocolchicine and analogues derived thereof a tricyclic 6-7-6-system have been found as key scaffold of various biologically relevant molecules. However, the direct preparation of the allocolchicine motif remains difficult to date. Herein, we report on an electrooxidative radical cyclization of biarylynones with various carbon- and heteroatom-centered radical precursors via a sequential radical addition/7-endo-trig/radical cyclization domino reaction. This approach provides a step-economical and strategically novel disconnection for the facile assembly of a wide range of carbocyclic 6-7-6 fused ring systems. Remarkably, the sulfonyl group on the products could be easily removed by photocatalysis at room temperature with high yields.

Dibenzocycloheptanones construction through a removable P-centered radical: synthesis of allocolchicine analogues.

Dibenzocycloheptanones containing a tricyclic 6-7-6-system are present in numerous biologically active natural molecules. However, the simple and efficient preparation of derivatives containing a dibenzocycloheptanone scaffold remains difficult to date. Herein, we report a versatile strategy for the construction of these challenging seven-membered rings using a 7-endo-trig cyclization which is initiated by a phosphorus-centered radical. This approach provides a step-economical regime for the facile assembly of a wide range of phosphorylated dibenzocycloheptanones. Remarkably, we also have devised a traceless addition/exchange strategy for the preparation of dephosphorylated products at room temperature with excellent yields. Therefore, this protocol allows for the concise synthesis of biorelevant allocochicine derivatives.