The diagnosis and staging of breast cancer could be improved by the development of imaging radiopharmaceuticals that provide a noninvasive determination of the estrogen receptor status in the tumor cells. Toward this goal, we have synthesized a number of novel Re-containing 7α-substituted estradiol complexes. The introduction of the 7α side chain involves the alkylation of tetrahydropyranyloxy-protected 6-keto estradiol. The methods ...