Steroids. Part 21. Photorearrangement of steroidal nitronate salts and a N-butyl spiro-oxaziridine

Steroids Part 22. Photochemistry of 5,6-epoxy-4,4-dimethylcholestan-3-ones and 5,6-epoxy-17-hydroxy-4,4-dimethylestran-3-ones

“…However, similar effects may also allow rationalisation of our earlier observations on the photochemistry of the 6-keto 9,lOepoxides (1) and (2). The diradical (40; 9a,10a) would not readily achieve the planar conformation at C-5 in which the semioccupied orbital is coplanar with the C-9-0 bond owing to a severe steric interaction between the 5-methyl group and the 7-methylene group.…”

“…We report here an investigation of the photoreactions of the 5,6-epoxy-4,4dimethylcholestan-3-ones (5) and ( The 3-keto 19-nor-5~,6a-epoxide (7) was prepared by monoperphthalic acid oxidation of the A5-compound (10) and the 5P,6P-epimer (8) was obtained from the latter by successive treatment with N-bromosuccinimide (NBS)-aqueous perchloric acid and potassium acetate. Similar photolysis of the 3-keto 5P,6P-epoxide (6) led to rapid decarbonylation and the unsaturated 5P,6P-epoxide (1 1) (29%) and the 4-nor-SP,6P-epoxide (12) (12%) were isolated after preparative t. 1 compound showed singlets for the methyl groups of the 5isopropyl group (6 0.72 and 0.85), confirming that deuterium is transferred from C-2 to C-4 in the photolysis. spectra of the epoxides (7) and (8) respectively at 6 3.14 ( J 5 Hz) and 3.18 (J 3 Hz) confirmed the assigned stereo~hemistry.~ Photolysis of the 3-keto 5a,6a-epoxide (5) in ether solution in Pyrex apparatus, using a medium-pressure Hg lamp, afforded an extremely complex inseparable mixture.…”

“…The photoreactions of the 9,l0-epoxy-19-norcholestan-6-ones (1) and (2)2 are not fully rationalised by the general Scheme 1 proposed for the photolyses of P,y-epoxy ketones of this type. In particular, there is a significant difference in reactivity between isomers (1) and (2) and the decarbonylation of compound (2) in ether appears to involve an unusual 1,5hydrogen transfer., The absence of products arising from cleavage of the epoxide moiety is interesting since, in general, the radicals (a) (Scheme 1) might be expected4 readily to give oxide radicals (b) especially since stereoelectronic effects have been reported to be unimportant in this type of r e a~t i o n .~ The photoreactions of the l-oxaspiro[2.n]alkan-5-ones (3) and (4) are reported6 to be adequately accounted for by a reaction scheme which is analogous to Scheme 1.…”

Inhibition of 2,3-oxidosqualene cyclases

“…The imine was prepared from ketone XVIII, and the imine double bond was selectively oxidized. The resulting oxaziridine, XIX, upon photolysis (Marples et al, 1984) in cyclohexane gave an amide in fairly good yield. The exclusive formation of the desired stereoisomer suggests that a concerted mechanism was involved in the ring expansion reaction.…”