The earlier described reaction of homophthalic anhydrides with aromatic ketones and
ammonium acetate was tested for cyclic ketones (yielding spirocyclic motifs) and aliphatic
aldehydes. In contrast to previous findings, the reaction was found to require no
catalyst at all and to be applicable, in the non-catalyzed format, to these new carbonyl
substrates as well as aromatic ketones. The reaction typically proceeds with high
diastereoselectivity; if not, the initial diastereomeric mixture can be quantitatively
equilibrated into a single, trans-diastereomer on treatment with aqueous base.
Key words
Castagnoli–Cushman reaction - homophthalic anhydride - tetrahydroisoquinolonic acids
- catalyst-free - spirocyclic compounds - diastereoselectivity
