A New Central Binaphthalene Building Block for Michellamine Syntheses

The synthesis of a new, suitably protected and activated binaphthalene building block representing the central structural element of all known natural dimeric naphthylisoquinoline alkaloids, is described. This functionalized fragment possesses organometallically robust O-isopropyl (instead of O-acetyl) protecting groups and bromo (instead of trifluoromethanesulfonyloxy) activation at the scheduled coupling positions. Starting from a biphenyl intermediate, the construction of the two `outer' naphthalene rings has been achieved by a Wittig reaction → cyclization sequence.