Preparation of 3-heterospiro[5.5]undec-7-en-9-ones

The Robinson annulation to 3-heterospiro[5.5]undec-7-en-9-ones (A) was carried out under basic conditions using Triton B solution [5] for all cases except 3-oxaspiro[5.5]undec-7-en-9-one, which was prepared in a higher yield under acidic conditions using phosphoric acid.

a: X = N-CH3, N-COOC(CH3)3, S: MVK, Triton B/ButOH; yields: 40 - 50%; X = O: MVK, H3PO4/benzene; yield: 70%

3-Heterospiro[5.5]undec-7-en-9-ones (A) serve as key intermediates. From this class of compounds ketones (B) are accessible via reduction methodology and dienones (C) are accessible via oxidation methodology. Both types of compounds, ketones and dienones, enable transformations to various heterocyclic target systems.