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 hydrogenation, and subsequent annelation with potassium t- butoxide . Application of the model study to the synthesis of a CD intermediate, through the use of the conjugate addition of lithiated butenyldiphenylphosphine oxide (2) to 2-methylcyclopentenone (1), followed by trapping with the electrophile (3), was not straightforward. Hydrogenation of the adduct (12) proceeded with loss of stereoselectivity. Instead, use of the alternative electrophiles, the α-( trimethylsilyl ) butadienyl sulfones (18) and (19), gave the desilylated unsaturated adduct (22). Hydrogenation of (22) proceeded smoothly to give the saturated adduct (15) as one isomer. However, in contrast to the model study, attempts at cyclization of the CD intermediate precursor (15) were unsuccessful.
The preparation of some novel four-carbon electrophiles and electrophile intermediates is described. Thus, the chlorobutenyl sulfone (5), the iodobutynyl sulfone (6) and the hitherto unreported chlorobutynyl sulfone (4) were prepared. The novel intermediates, containing a chelating imidazolyl functionality, the N- methylimidazolyl sulfides (13)-(15) were also prepared. However, they polmerized rapidly, thus preventing further synthetic manipulations. The preparation of the α-( trimethylsilyl ) butadienyl sulfones (17) and (18) is described and the mode of formation of the intermediate α- trimethylsilyl sulfides (21) and (22) from the trimethylsilylbutenyl sulfide (27) is discussed.