Circular dichroism, nuclear magnetic resonance, and crystal structure of 4α-bromo-5α-androst-2-ene-1,17-dione

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Abstract
The stereochemistry of the bromination of 5α-androst-2-ene-1,17-dione with N-bromosuccinimide has been established by examination of the circular dichroism, nuclear magnetic resonance, and crystal structure of the product, which is shown to be 4α-bromo-5α-androst-2-ene-1,17-dione. The bromo-steroid crystallizes in the orthorhombic space group P212121, with Z= 4 in a unit cell of dimensions a= 9·894, b= 25·77, c= 6·636 Å. The X-ray intensities were measured on a four-circle diffractometer with Mo-Kα radiation. The atomic co-ordinates were determined by Fourier and least-squares methods, and R converged to 8·1% over 902 independent reflections. The hydrogen atoms were unambiguously located in a difference electron-density distribution. The conformation of ring D approximates closely to an envelope form, with C(14) the out-of-plane atom. Rings B and C have chair conformations for which the torsion angles, apart from the angle associated with the C(13)–C(14) bond at the C–D ring junction, are smaller than 60°. From the X-ray results the H–C(3)–C(4)–H and H–C(4)–C(5)–H torsion angles are –85°± 5° and –167°± 5°, respectively, and the n.m.r. measurements show that J3,4 is 2 Hz and J4,5 9 Hz; the magnitudes of the 3–4 torsion angle and coupling constant are in accord with Garbisch's treatment of vinyl spin couplings.

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