Participation of ambident neighbouring groups in hypobromous acid addition to some steroidal olefins. Competition of electronic and stereoelectronic effects

1987 ◽  
pp. 1969-1974 ◽  
Author(s):  
Pavel Kočovský ◽  
Irena Stieborová
Keyword(s):  
Stereoelectronic Effects ◽  
Acid Addition ◽  
Hypobromous Acid

Participation of 19-substituents in electrophilic additions. influence of 3β-substitution on hypobromous acid addition to 5,6-unsaturated steroids

1980 ◽  
Vol 45 (11) ◽  
pp. 3023-3029 ◽  
Author(s):  
Pavel Kočovský ◽  
Václav Černý
Keyword(s):  
Acid Addition ◽  
Hypobromous Acid ◽  
Electrophilic Additions ◽  
Competing Reactions

Reactions of 19-hydroxy-, methoxy- and acetoxy-5-cholestenes Ia, IIa, IIIa were studied and compared with those previously obtained with analogous 3β-acetoxy-19-substituted 5-cholestenes Ib, IIb, IIIc. A marked difference was found in 19-acetoxy derivatives where the 3-unsubstituted compound IIIa yields exclusively the bromohydrin XVIa as a product of 6(O)π,n participation while the 3β-acetoxy derivative IIIb gives, apart from the analogous bromohydrin XVIb, also products of competing reactions: The epoxide XIIb and the bromohydrin XIIIb.

Participation by some oxygen containing groups in hypobromous acid addition to double bond

1983 ◽  
Vol 48 (12) ◽  
pp. 3660-3673 ◽  
Author(s):  
Pavel Kočovský
Keyword(s):  
Double Bond ◽  
Functional Groups ◽  
Relative Reactivity ◽  
Product Analysis ◽  
Acid Addition ◽  
Hypobromous Acid ◽  
Electron Withdrawing Substituents

5(O)n and 6(O)π,n participations by some oxygen containing functional groups in the course of reaction with hypobromous acid have been studied on olefinic models of steroid type (I and II). The ability of these groups to participate has been compared on the basis of their relative reactivity with water (as externally attacking nucleophile) competing with participation. The results of the product analysis show that the ability to react with 5(O)n participation decreases in the order HO > CH3O ≃ CH3OCH2O > CH3CO2 > HCO2 > CH3SO3 ≥ (C2H5O)2PO2 > C6H5CO2 > O2NO ≫ CF3CO2, C2H5OCO2; in the last two functional groups is this ability completely suppressed. The 6(O)π,n participation comes in consideration only for compounds of the type II bearing the groups with the -X=O moiety which are ordered in the following sequence: C2H5OCO2 ≃ CH3CO2 ≥ (C2H5O)2PO2 > HCO2 > C6H5CO2. The remaining functional groups (CF3CO2, O2NO and CH3SO3do not undergo this process. Generally, it is valid that introduction of electron-withdrawing substituents into a participating group impedes or completely suppresses its ability to participate.

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.

Synthesis of D-norisomorphinans ((±)-[14α]-D-normorphinans)

1985 ◽  
Vol 63 (5) ◽  
pp. 1013-1017 ◽  
Author(s):  
John P. Yardley ◽  
Richard W. Rees
Keyword(s):  
Intramolecular Cyclization ◽  
Ring System ◽  
Acid Addition ◽  
Hypobromous Acid ◽  
Synthetic Target

A synthesis of the D-norisomorphinan ring system is described. Conversion of the initial synthetic target, trans-1,3,4,9,10,10a-hexahydro-6-methoxy-9-oxo-4a(2H)-phenanthrenecarboxamide (10c) into the D-norisomorphinan (6b) proved possible only after removal of the carboxamide ambident functionality. The successful route proceeds via hypobromous acid addition to trans-1,3,4,10a-tetrahydro-6-methoxy-4a(2H)-phenanthrenemethanamine (21) followed by a facile intramolecular cyclization to the D-norisomorphinan (23).

Synthesis of 14-deoxy-14α-strophanthidol

1980 ◽  
Vol 45 (3) ◽  
pp. 921-926 ◽  
Author(s):  
Pavel Kočovský ◽  
Václav Černý
Keyword(s):  
Characteristic Feature ◽  
Title Compound ◽  
Acetoxy Group ◽  
Hydroxyl Group ◽  
Acid Addition ◽  
Hypobromous Acid

A thirteen-step synthesis of 3β,5,19-trihydroxy-5β, 14α-card-20(22)-enolide (I, title compound) from 3β-acetoxy-5-pregnen-20-one (V) is described. A characteristic feature of this approach is the introduction of the 5β-hydroxyl group by hypobromous acid addition to the 5,6-unsaturated-19-acetoxy derivative XV which proceeds with 6(O)π n participation of the acetoxy group (XV(r)XVI(r)XVII).

Competition of two participating groups in hypobromous acid addition to some 4-cholestene derivatives

1983 ◽  
Vol 48 (12) ◽  
pp. 3643-3659 ◽  
Author(s):  
Pavel Kočovský
Keyword(s):  
Hydroxy Group ◽  
Acid Addition ◽  
Hypobromous Acid

Hypobromous acid addition to the 4,5-unsaturated hydroxy acetate VIII results in formation of the cyclic bromo ether XXIXa as a product of 5(O)n participation. Participation by hydroxy group is thus preferred over 5(O)π,n process by acetoxyl. Under the same conditions the 4,5-unsaturated diacetate IX afforded the diaxial bromohydrin XXXI arising from 4α,5α-bromonium ion with 5(O)π,n participation by the 3β-acetoxyl whereas an alternative 6(O)π,n participation by the 19-acetoxyl is not operative. The 3-epimeric diacetate XV reacts with hypobromous acid in a more complex way: the molecule is attacked by the electrophile from both α- and β-sites to give two diastereoisomeric bromonium ions XXXII and XXXIII. The former is simply cleaved with water as an external nucleophile to afford the diaxial bromohydrin XXXIV. The latter undergoes fission both with 5(O)π,n and 6(O)π,n participation: The first route leads to the trans-bromohydrin XXXVI. In the second pathway the acyloxonium ion XXXVII postulated as an intermediate is further cleaved with 6(O)π,n participation by 19-acetoxyl to give the acyloxonium ion XXXVIII, which is trapped by water to yield an unusual cis-bromohydrin XXXIX. The differences in the reaction course are discussed.

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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