Westphalen rearrangement. Mechanism of formation of 5α-acetoxy derivatives

1979 ◽  
Vol 44 (1) ◽  
pp. 234-245 ◽  
Author(s):  
Pavel Kočovský ◽  
Václav Černý ◽  
František Tureček
Keyword(s):  
Mechanism Of Formation ◽  
Neighboring Group ◽  
Group Participation ◽  
Rearrangement Mechanism ◽  
Neighboring Group Participation ◽  
By Products

5α-Acetoxy derivatives formed as by-products in the course of Westphalen rearrangement of [5-18O]-5-hydroxy-5α-cholestanes Ia and Ib are shown to preserve their 18O content. This fact rules out previously proposed neighboring group participation of the 6β-substituent involving a 5β,6β-„onium" intermediate (F).

Neighboring group participation in hypobromous acid addition to 19-substituted 5α-cholest-1-enes and in acid cleavage of their epoxy analogs

1982 ◽  
Vol 47 (11) ◽  
pp. 3062-3076 ◽  
Author(s):  
Václav Černý ◽  
Pavel Kočovský
Keyword(s):  
Neighboring Group ◽  
Group Participation ◽  
Acid Addition ◽  
Acid Cleavage ◽  
Hypobromous Acid ◽  
Neighboring Group Participation

Reactions of the title compounds (bearing an OH, OCH3 or OCOCH3 group at C(19)) involve 5(O)n, 7(O)π,n-participation by the 19-substituent or attack by an external nucleophile. The 6(O)π,n-participation does not occur. The behavior of 1,2-unsaturated (or epoxidated) compounds has been compared with the earlier described 2,3-unsaturated or epoxidated analogs. The 1,2-type is genarally less prone to participation. The reasons for this behavior are discussed.

Mechanism of acid cleavage of some steroid epoxides. Competition between neighboring group participation and external nucleophile attack

1982 ◽  
Vol 47 (1) ◽  
pp. 124-129 ◽  
Author(s):  
Pavel Kočovský ◽  
František Tureček ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Cyclic Ether ◽  
Oxirane Ring ◽  
Neighboring Group ◽  
Group Participation ◽  
Acid Cleavage ◽  
Neighboring Group Participation

The mechanism of perchloric acid cleavage of epoxides I and II was established on the basis of experiments using H2 18O. The 2α,3α-epoxide I gave two products: the cyclic ether V (60%) arising by 5(O)n participation of the 19-acetoxyl and the diol VI (40%). The latter compound is formed by two mechanisms: 1) By direct cleavage of the oxirane ring with H2 18O as external nucleophile and 2) by 7(O)π,n participation via the ion III. Under the same conditions the 5α,6α-epoxide II yielded two diols: The diequatorial diol VIII (96%) arising by 6(O)π,n participation and the diaxial diol IX which is again formed by both direct cleavage of the oxirane ring with H2 18O and by 7(O)π,n participation via the intermediate ion X. The competition of several mechanisms is discussed.

ChemInform Abstract: Remote Asymmetric Induction Using Neighboring Group Participation of a Sulfenyl Group.

ChemInform ◽  
2010 ◽  
Vol 25 (49) ◽  
pp. no-no
Author(s):  
Y. HASHIMOTO ◽  
Y. SATO ◽  
N. TAKESHITA ◽  
K. KUDO ◽  
K. SAIGO
Keyword(s):  
Asymmetric Induction ◽  
Neighboring Group ◽  
Group Participation ◽  
Neighboring Group Participation

Neighboring group participation in radicals: pulse radiolysis studies on radicals with sulfur-oxygen interaction [Erratum to document cited in CA107(11):96206Y]

1988 ◽  
Vol 53 (21) ◽  
pp. 5192-5192
Author(s):  
Sabine Mahling ◽  
Klaus Dieter Asmus ◽  
Richard S. Glass ◽  
Massoud Hojjatie ◽  
Mahmaad Sabahi ◽  
...  
Keyword(s):  
Pulse Radiolysis ◽  
Neighboring Group ◽  
Group Participation ◽  
Neighboring Group Participation ◽  
Oxygen Interaction
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