Selective C-7 Functionalization of Phenanthridines by Microwave-Assisted Claisen Rearrangements of 8-Allyloxyphenanthridines

Carbon-carbon bond formation in the phenanthridine 7-position was achieved by microwave-assisted Claisen rearrangement of 8-allyloxyphenanthridines. The reactions took place with excellent regioselectivity and high chemical yields. If the 7-position was substituted, rearrangement to C-9 took place, but the reaction occurred less readily. Rearrangements of 8-allyloxy-5,6-dihydrophenanthridines (phenanthridines with a saturated B-ring) gave a mixture of 7- and 9-substituted products. The experimental results were supported by DFT (density functional theory) calculations.

Automated summary

Microwave-assisted Claisen rearrangement of 8-allyloxyphenanthridines allows for the formation of carbon-carbon bonds at the phenanthridine 7-position. The reaction exhibits excellent regioselectivity and high chemical yields. If the 7-position is substituted, rearrangement to C-9 occurs with lower reactivity. Rearrangement of 8-allyloxy-5,6-dihydrophenanthridines (phenanthridines with a saturated B-ring) results in a mixture of products at both the 7- and 9-positions. DFT calculations support the experimental findings.