A new regiospecific method for the synthesis of substituted phenanthridines and benzo[j]phenanthridines via aromatic annelation of 1-N- benzenesulfonyl-3-[bis(methylthio)methylene]1,2,3,4-tetrahydroquinoline-4- one

Article abstract of DOI:10.1016/S0040-4020(98)00609-7

A new efficient method for the synthesis of substituted phenanthridines, benzo[j]phenanthridines and naphtho[2,1-j]phenanthridines is described. The method involves reaction of α-oxoketene dithioacetal 2 with allyl (3a), methallyl (3b), benzyl (11a-f) and 1-naphthylmethyl (20) magnesium halides followed by cyclization of the resulting carbinolacetals in the presence of BF₃Et₂O in refluxing benzene. The dihydrophenanthridines thus obtained were aromatized by treatment with a base in the presence of phase transfer catalyst.