Neighboring-group participation in carbohydrate chemistry. III. Neighboring-group participation of the 6-hydroxyl group in a nucleophilic displacement of a 5-p-toluenesulfonate

1972 ◽  
Vol 37 (16) ◽  
pp. 2536-2540 ◽  
Author(s):  
M. Miljkovic ◽  
D. Miljkovic ◽  
A. Jokic ◽  
V. Andrejevic ◽  
E. A. Davidson
Keyword(s):  
Hydroxyl Group ◽  
Carbohydrate Chemistry ◽  
Neighboring Group ◽  
Group Participation ◽  
Nucleophilic Displacement ◽  
Neighboring Group Participation

Neighboring group participation in electrophilic additions: The role of Markovnikov and Fürst-Plattner rule in hypobromous acid addition to 5,6-unsaturated cholestane derivatives

1983 ◽  
Vol 48 (12) ◽  
pp. 3618-3628 ◽  
Author(s):  
Pavel Kočovský
Keyword(s):  
Methyl Ether ◽  
Hydroxyl Group ◽  
Unsaturated Alcohol ◽  
Neighboring Group ◽  
Group Participation ◽  
Acid Addition ◽  
Hypobromous Acid ◽  
Neighboring Group Participation ◽  
Electrophilic Additions

On reaction with hypobromous acid, the unsaturated alcohol IIIa yields the diequatorial bromo epoxide XIX arising from the 5α,6α-bromonium ion XVIIIa on cleavage at C(5) by 19b-hydroxyl group with 6(O)n participation. By contrast, the bromonium ion XVIIIb generated from the unsaturated methyl ether IIIb is cleaved by water as external nucleophile to yield the unstable diaxial bromohydrin XX which undergoes cyclization to the oxirane derivative XXI. A comparison with the reaction course in homologs of the type I and II permits the conclusion that the change in regioselectivity, generally possible outcome of the 5(O)n participation, is only possible for the 6(O)n process if the participating group is a hydroxyl.

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