Diastereoselective Strategy for Stereotetrads Synthesis

Significance

With this new strategy to access polypropionate fragments, an epoxide was ring-opened by the S_N2′ addition of 3,5-dimethylpyrra­zole to provide the isolable pyrrazole allylic alcohol. An alkoxide-directed Grignard addition ejected the pyrrazole moiety (second S_N2′). Out of several methyl nucleophiles examined, only the organomagnesium reagents gave the desired products 3 and 6. The oxidative cleavage of the heptene rings yielded the stereotetrads 7 and 8 with chemically differentiated termini.