alkylarylstannanes is such a method. The corresponding versatility of the trialkylvinylstannanes has been less well defined. In the present study we have clearly demonstrated that a polyfunctional precursor, the (E)-2l-(tri-n-butylstanny1)-( 1701)-19-norpregna-1,3,5( 10) ,20-tetraene-3,17@-diol, which can be prepared in good yields with the defined E stereochemistry, undergoes facile ipso substitution with a variety of electrophiles. These reactions which include protonation, deuteriation, halogenation, and phenylselenation proceed at ambient temperatures or lower, within 1-30 min, except in the case of the phenylselenation. In all cases a single product resulting from ipso substitution is obtained in isolated yields of 76-97%. The compounds could be identified by the mass spectra which provided the parent ions, and the stereochemistry could be clearly assigned as the basis of the vinylic coupling constants. No evidence of electrophilic reactions of electrophilic reactions on the unprotected phenolic A ring could be detected. This supports our selection of the trialkylstannyl moiety for activation of sp2 carbon bonds toward electrophilic substitution in the development of radiopharmaceuticals labeled with the radionuclides of hydrogen, selenium, bromine, or iodine.
Experimental SectionGeneral Methods. IR spectra were obtained via a Perkin-Elmer Model 599B infrared spectrophotometer. 'H and ' % NMR spectra were taken at ambient temperature in CDCH,, CD3CO-CH3, or CD30D, with tetramethyleilane as an internal standard on a Varian 300-MHz instrument. Tetrahydrofuran (THF) was distilled under nitrogen from sodium benzophenone ketyl. Flash chromatography employed silica gel (230-400 mesh) as the absorbent. Thin layer chromatography was performed on both normal (silica gel) and reverse phase (C-18) plates using chloroform/ethyl acetate (91) and ethanol/water (91) as the eluents.The n-butyllithium, trifluoroacetic acid, trifluoroacetic anhydride, deuterium oxide, diphenyl diselenide, iodine, and bromine were obtained commercially from Aldrich Chemical Co. and used without further purification. (17a,20E)-21-(Tri-n -butylstannyl)-19-norpregna-1,3,5-(10),2O-tetraene-3,17-diol (1). This compound was synthesized from estrone and (E)-1,2-bis(tri-n-butylstannyl)ethene according to the procedure of Hanson et al:5 ' H NMR (CDCl,) 6 0.67-2.67 (41, H, m, steroid nucleus plus (n-C,H,), 2.67-2.93 (3 H, m), 6.12 (E)-1,2-bis(tri-nbutylstannyl)ethene, 14275-61-7. 6.44 (d, J = 3 Hz, Cd-H), 6.47 (dd, J = 3 Hz, J = 3 Hz, Cz-H), 6.60 (d, J = 16 Hz, CZO-H), 7.10 (d, J = 8 Hz, Cl-H), 7.21-7.46Thiocarbamate herbicides are used extensively worldwide for controlling the growth of undesirable plant species. These herbicides are relatively nonpersistent in the environment, but the preferred mode of degradation is not well established.*,* Thermal reactions could be an
