Thiophenol-Mediated 1,5-Hydrogen Transfer for the Preparation of Pyrrolizidines, Indolizidines, and Related Compounds

2007 ◽  
Vol 9 (21) ◽  
pp. 4375-4378 ◽  
Author(s):  
Fabrice Dénès ◽  
Florent Beaufils ◽  
Philippe Renaud
Keyword(s):  
Hydrogen Transfer ◽  
Related Compounds

Photochemistry of cyclic α-hydroxy ketones. I. The nature and genesis of the photoproducts from steroidal 5-hydroxy 6-keto steroids and related compounds

1988 ◽  
Vol 66 (2) ◽  
pp. 214-226 ◽  
Author(s):  
Shirley Stiver ◽  
Peter Yates
Keyword(s):  
Hydrogen Transfer ◽  
Deuterium Atom ◽  
Radical Center ◽  
Nonplanar Geometry ◽  
Restricted Rotation ◽  
Development Control ◽  
Preferred Direction ◽  
Hydroxyalkyl Radical ◽  
Major Factors ◽  
Related Compounds

Photolyses of 5-hydroxy-5α- and 5β-cholestan-6-one and their 3β-acetoxy- and 3β-benzyloxy derivatives 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 stereospecifically 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.

Flavin catalysis of hydrogen transfer from dihydropyridines and related compounds

1965 ◽  
Vol 14 (9) ◽  
pp. 1657-1659
Author(s):  
D. D. Mozzhukhin ◽  
M. L. Khidekel' ◽  
E. N. Aleksandrova ◽  
S. N. Zelenin ◽  
V. M. Berezovskii
Keyword(s):  
Hydrogen Transfer ◽  
Related Compounds
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