STUDIES TOWARDS CD-INTERMEDIATES OF VITAMIN-D-3 - ENOLATE TRAPPING OFKETONE ENOLATES WITH NOVEL SULFONYL ELECTROPHILES

The phenyl sulfonyl electrophile (3) reacts with the titanium enol of cyclopentanone to provide an alkylated adduct (8). Conversion into the model hydrindanol (11) [71% from (8)] was readily effected by hydroge nation, and subsequent annelation with potassium t-butoxide. Applicati on of the model study to the synthesis of a CD intermediate, through t he use of the conjugate addition of lithiated butenyldiphenylphosphine oxide (2) to 2-methylcyclopentenone (1), followed by trapping with th e electrophile (3), was not straightforward. Hydrogenation of the addu ct (12) proceeded with loss of stereoselectivity. Instead, use of the alternative electrophiles, the alpha-(trimethylsilyl)butadienyl sulfon es (18) and (19), gave the desilylated unsaturated adduct (22). Hydrog enation of (22) proceeded smoothly to give the saturated adduct (15) a s one isomer. However, in contrast to the model study, attempts at cyc lization of the CD intermediate precursor (15) were unsuccessful.