93748-64-2Relevant academic research and scientific papers
STEREOSPECIFICITY IN THE PHOTOISOMERIZATION OF STEROIDAL α-KETOLS TO LACTONES
Stiver, Shirley,Yates, Peter
, p. 3289 - 3292 (1984)
The photoisomerization of 5-hydroxy-6-cholestanones to lactones involves ketene intermediates formed by migration of H-7α; its stereospecificity is independent of hydrogen bonding and is attributed to slowing of rotation about the C-9 - C-10 bond in the alkyl acyl diradicals that are the ketene precursors.
Photochemistry of cyclic α-hydroxy ketones. I. The nature and genesis of the photoproducts from steroidal 5-hydroxy 6-keto steroids and compounds
Stiver, Shirley,Yates, Peter
, p. 214 - 226 (2007/10/02)
Photolyses of 5-hydroxy-5α- and 5β-cholestan-6-one and their 3β-acetoxy- and 3β-benzyloxy derivates in benzene or ethanol proceed stereospecifically with retention of configuration at C-5 to give the corresponding lactones, 6-oxa-B-homocholestan-7-ones.Photolyses of 3β-acetoxy-7α-deutero-5-hydroxy-5α- and 5β-cholestan-6-ones also proceed sterospecifically to give the corresponding 5-deutero lactones. 3β-Acetoxy-5-deuteroxy-5α- and 5β-cholestan-6-one give on irradiation 1:3 and 7:1 mixtures, respectively, of the corresponding 7aα- and 7aβ-deutero lactones.Irradiation of 3β-acetoxy-5-methoxy-5α-cholestan-6-one in ethanol leads to the stereoselective formation of ethyl 3β-acetoxy-5-methoxy-5,6-seco-5α-cholestan-6-oate, while that of 3β-acetoxy-5α-cholestan-6-one gives mainly photoreduction products.These observations are interpreted in terms of α-cleavage of the C-5 - C-6 bond of the ketols to give alkyl acyl diradicals that undergo hydrogen transfer to give hydroxy ketenes, which then form the lactones.It is proposed that retention of configuration at C-5 results from two major factors - the nonplanar geometry of the hydroxyalkyl radical center, and fast hydrogen transfer in the diradical, the latter resulting from restricted rotation about the C-9 - C-10 bond.The specific transfer of the 7α-deuterium atom in the 7α-deutero ketols is attributed to these factors and to the preferred direction of opening to the diradical on α-cleavage.The O-deuterium labelling results are interpreted in terms of product development control in the conversion of the hydroxy ketenes to the lactones and are in accord with restricted rotation about the C-9 - C-10 bond.The photolysis of 3β-acetoxy-5-amino-5α-cholestan-6-one proceeds stereoselectively to give the 5β-lactam analogue of the 5β-lactone formed from the analogous 5α-ketol.
