Reductive cyclization of aryl and vinyl iodides tethered to vinylogous acyl triflates (VATs) induces a ring-expanding fragmentation to provide cyclic alkynyl ketones, including strained nine-membered cycloalkynes, in fair to excellent yield. The tandem cyclization/C-C bond-cleavage is initiated under carefully optimized conditions by halogen-metal exchange in the presence of carbonyl and vinyl triflate functionality. A modified protocol for alkylation of 1,3-cyclohexanedione is described for preparing the relevant VAT substrates.
A new and mild synthetic approach for the synthesis of 6-unsubstituted phenanthridine and phenanthridine-like compounds under metal-free conditions at room temperature has been developed. The strategy involved a tandem azide rearrangement/intramolecular annulation and oxidation reactions of biarylmethyl azide precursors to obtain the desired products in up to 99% yields with high regioselectivity.
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