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The conformations of (Z)‐ and (E)‐5‐oxo‐B‐nor‐5,10‐secocholest‐1(10)‐en‐3β‐yl acetates (2 and 3, resp.) were examined by a combination of X‐ray crystallographic analysis and NMR spectroscopy, with emphasis on the geometry of the cyclononenone moiety. The 1H‐ and 13C‐NMR spectra showed that the unsaturated nine‐membered ring of (E)‐isomer 3 in C6D6 and (D6)acetone solution exists in a sole conformation of type B1, which is similar to its solid‐state conformation. The (Z)‐isomer 2 in C6D6, CDCl3, and (D6)acetone solution, however, exists in two conformational forms of different families, with different orientation of the carbonyl group, the predominant form (85%) corresponding to the conformation of type A1 and the minor (15%) to the conformation A2 present also in the crystalline state. In this solid‐state conformations of the nine‐membered ring of both compounds, the 19‐Me and 5‐oxo groups are ‘β’‐oriented. The NMR analysis suggests that the nine‐membered ring of 4 has a conformation of type C1 in CDCl3 solution.

Oxidations of 5α‐hydroxy‐B‐norcholestan‐3β‐yl acetate (8) with Pb(OAc)4 under thermal or photolytic conditions or in the presence of iodine afforded only complex mixtures of compounds. However, the HgO/I2 version of the hypoiodite reaction gave as the primary products the stereoisomeric (Z)‐ and (E)‐1(10)‐unsaturated 5,10‐seco B‐nor‐derivatives 10 and 11, and the stereoisomeric (5R,10R)‐ and (5S,10S)‐acetals 14 and 15 (Scheme 4). Further reaction of these compounds under conditions of their formation afforded, in addition, the A‐nor 1,5‐cyclization products 13 and 16 (from 10) and 12 (from 11) (see also Scheme 6) and the 6‐iodo‐5,6‐secolactones 17 and 19 (from 14 and 15, resp.) and 4‐iodo‐4,5‐secolactone 18 (from 15) (see also Scheme 7). Oxidations of 5β‐hydroxy‐B‐norcholestan‐3β‐yl acetate (9) with both hypoiodite‐forming reagents (Pb(OAc)4/I2 and HgO/I2) proceeded similarly to the HgO/I2 reaction of the corresponding 5α‐hydroxy analogue 8. Photolytic Pb(OAc)4 oxidation of 9 afforded, in addition to the (Z)‐ and (E)‐5,10‐seco 1(10)‐unsaturated ketones 10 and 11, their isomeric 5,10‐seco 10(19)‐unsaturated ketone 22, the acetal 5‐acetate 21, and 5β,19‐epoxy derivative 23 (Scheme 9). Exceptionally, in the thermal Pb(OAc)4 oxidation of 9, the 5,10‐seco ketones 10, 11, and 22 were not formed, the only reaction being the stereoselective formation of the 5,10‐ethers with the β‐oriented epoxy bridge, i.e. the (10R)‐enol ether 20 and (5S,10R)‐acetal 5‐acetate 21 (Scheme 8). Possible mechanistic interpretations of the above transformations are discussed.

Oxidations of 14α‐hydroxy‐5α‐cholestan‐3β‐yl acetate (5) with lead tetraacetate under thermal or photolytic conditions or in the presence of iodine proceed mainly by fragmentation of the C(13)−C(14) bond to give as the primary products the 13,18‐didehydro‐13,14‐seco derivative 6 and the (E )‐Δ12‐13,14‐seco ketone 11, respectively. Further transformations of these compounds under conditions of their formation afforded, in addition, the acetoxy derivatives 7 – 9 (from 6), and the D‐homo‐C‐nor compound 12 and (12R,13R)‐epoxide 13 (from 11). Unexpectedly, the photolytic lead‐tetraacetate oxidation of 5 resulted partly (to ca. 20%) in a reversible fragmentation involving scission and recombination of the C(8)−C(14) bond followed by formation of the 14β,22‐ether 10. Possible mechanisms for the observed transformations are discussed.

The two structurally similar 20‐phenyl‐ and 20‐(4‐methoxyphenyl)‐11‐(nitrosooxy)pregnan‐20‐ol derivatives 4 and 7 behave differently under photolytic conditions, the former nitrous acid ester affording, as a main product, the benzo‐fused hexacyclic compound 9, and the latter the 21‐nitro derivative 12. Mechanistic aspects of these transformations are discussed.

Unsubstituted medium‐ring 1,2‐epoxycycloalkanes and certain vic‐epoxyalkanes are reduced to the corresponding alcohols very slowly when LiAlH4 alone is used as reducing agent. However, the combination of LiAlH4 and AlCl3, in a 2:1 molar ratio (with respect to 1 mol‐equiv. of epoxide) used in refluxing Et2O, greatly enhances these reductions, rendering them of interest for practical purposes.