Profe4yor of Chemistry, in charge of major

3,3-Dimethoxy-2,2-dimethylpropionaldehyde was prepared from isobutyr-aldehyde and formaldehyde in four steps. Heptanal, benzaldehyde, iso-butyraldehyde, 3,3-dimethoxy-2,2-dimethylpropionaldehyde, acetone, and cyclopentanone were each condensed with the dianions of crotonic acid and tiglic acid at-78°C, 25°C, and 65°C, and the proportions of the a and y condensation products were determined. The results indicated that the proportions of a and y condensation products are dependent on the steric size of the aldehyde or ketone, on the presence of a methyl substituent at the a carbon of the acid, on the reaction temperature, and on the duration of the reaction. A mechanism, which involves reversible formation of the a product and recombination to the y product is proposed. A required precursor to boromycin, 7,7-dimethoxy-5-hydroxy-2,6,6-trimethylheptanoic acid lactone was prepared by con-densing 3,3-dimethoxy-2,2-dimethylpropionaldehyde with the dianion of tiglic acid to give 7,7-dimethoxy-5-hydroxy-2,6,6-trimethy1-2-heptenoic acid. This acid was hydrogenated and lactonized to give the corresponding S-lactone