Synthesis of the ABC ring system of Azaspiracid. 2. A systematic study into the effect of C(16) and C(17) substitution on bis-spirocyclization.

[reaction: see text] A systematic study into the effect of C(16) and C(17) substitution on the stereochemical outcome of bis-spirocyclization to form the ABC ring system of azaspiracid is disclosed. Successful construction of the natural 10R,13R bis-spirocyclic stereochemistry has been accomplished on the C(16) benzyloxy-containing precursor.