Hydroxymethylation of protoberberine alkaloids by photoinduced SET. The total synthesis of(+/-)-solidaline

The direct insertion of a hydroxymethyl group at position C-8 in a protober berinium ion by photoaddition of methanol was approached via two mechanisti c pathways: acetone-sensitized and single-electron transfer. The latter pro duces 8-hydroxymethylberbines in good yields after reduction. By combining this photochemical reaction with the oxidation of the photoproduct, synthes es of (+/-)-solidaline and its C-13 epimer from palmatine chloride were acc omplished for the first time. On the other hand, insertion of a hydroxymeth yl group at position 14 of the berberine skeleton in order to open a synthe tic pathway for zijinlongine proved unsuccessful. (C) 1999 Elsevier Science Ltd. All rights reserved.