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.

Synthesis of 3,4-, 4,5- and 5,6-unsaturated 19-substituted cholestane derivatives and related epoxides

1980 ◽  
Vol 45 (11) ◽  
pp. 3008-3022 ◽  
Author(s):  
Pavel Kočovský
Keyword(s):  
Double Bond ◽  
Unsaturated Compound ◽  
Acid Addition ◽  
Hypobromous Acid

Starting from the 5,6-unsaturated compound X, 19-hydroxy-, 19-methoxy and 19-acetoxy derivatives with the double bond in positions 5,6- (XIV-XVI), 4,5- (XXI-XXIII) and 3,4- (XXX, XXXIII, XXXIV) were prepared by stepwise transposition of the 5,6-double bond. The route to 4,5-unsaturated steroids involves hypobromous acid addition (XVI → XVIII) followed by reductive removal of bromine and dehydration (XIX → XXI), Transposition of the 4,5-double bond to the 3,4-position is based on the conversion of the 4,5-olefin into 4β-alcohol (XXIII → XXVII) and pyrolysis of its benzoate (XXVIII → XXX).

Electrophilic additions to 10β-vinyl cholestane derivatives

1983 ◽  
Vol 48 (10) ◽  
pp. 2994-3019 ◽  
Author(s):  
Pavel Kočovský ◽  
Ivo Starý ◽  
František Tureček ◽  
Vladimír Hanuš
Keyword(s):  
Reaction Mechanism ◽  
Double Bond ◽  
Hydroxyl Group ◽  
Acid Addition ◽  
Hypobromous Acid ◽  
Markovnikov Rule ◽  
Vinyl Group ◽  
Electrophilic Additions

Hypobromous acid addition to steroid dienes I-VI proceeds in four steps. The reaction commences by the attack on more reactive endocyclic double bond from the α-side yielding intermediary diaxial bromohydrins XXVIII, XXXIV, XL, XLIV, L and LVI via corresponding α-bromonium ions. The 10β-vinyl group of the bromohydrins then reacts with a second equivalent of the reagent forming transient 19-epimeric bromonium ions. The ions generated from I, II, V and VI are cleaved intramolecularly by the hydroxyl group, in accordance with the Markovnikov rule, giving rise to 19-epimeric dibromo epoxides XXXIa and XXXIIa, XXXVII and XXXVIII, LIIIa and LIVa, LIX and LX. By contrast, the ions generated from III and IV are cleaved in an anti-Markovnikov manner to yield dibromo epoxides XLII, XLVII and XLVIII. Products due to formation of a new C-C bond were not observed. The reaction mechanism and differences in the behaviour of the dienes I-VI are discussed.

Competition of 5(O)n and 6(O)n participation by 19a-substituent in hypobromous acid addition to 2,3- and 5,6-unsaturated 19-homocholestane derivatives

1983 ◽  
Vol 48 (12) ◽  
pp. 3606-3617 ◽  
Author(s):  
Pavel Kočovský
Keyword(s):  
Functional Groups ◽  
Major Product ◽  
Unsaturated Alcohol ◽  
Methoxy Derivative ◽  
Acid Addition ◽  
Hypobromous Acid ◽  
Preceding Case

19-Substituted 2,3-unsaturated cholestane derivatives IIIa-IIIc react with hypobromous acid to give the cyclic bromo ether VI as sole or major product arising by cleavage of the 2α,3α-bromoion V with 6(O)n participation by the 19a-group. The 5,6-unsaturated alcohol IVa reacts with hypobromous acid to yield the cyclic bromo ether X as product of 5(O)n participation. Under the same conditions, the methoxy derivative IVb yields two products, X and XI, with violation of Fürst-Plattner rule. In similar manner as in the preceding case, the products arise by cleavage of the bromonium ion IXb with 5(O)n participation by the 19a-methoxyl. In contrast, the 5,6-unsaturated acetoxy derivative IVc reacts without participation via two diastereoisomeric bromonium ions VIIIc and XV to give the corresponding diaxial bromohydrins XVI and XVII which undergo spontaneous cyclization to the epoxides XVIII and XIX. The course of these reactions, comparison with the lower homologs of the type I and II, the role of Markovnikov and Fürst-Plattner rules and capability of the particular functional groups to participate in 5(O)n and 6(O)n processes are discussed.

An unusual rearrangement in hypobromous acid addition to 10β-vinyl cholestane derivatives

1981 ◽  
Vol 46 (11) ◽  
pp. 2892-2897 ◽  
Author(s):  
Pavel Kočovský ◽  
František Tureček
Keyword(s):  
Methyl Ether ◽  
Product Analysis ◽  
Acid Addition ◽  
Unusual Rearrangement ◽  
Hypobromous Acid

On treatment with hypobromous acid, 19-nor-10β-vinyl-5α-cholestan-5-ol (VIIa) rearranges to the spirocyclic ketone X. The rearrangement is postulated to proceed via the intermediate (19R)-bromonium ion VIIIa. The same reaction was observed with the methyl ether VIIb. The mechanism of the rearrangement was elucidated by 18O-labeling and product analysis.

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.

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.

Double bond terminated Ln3+-doped LiYF4 nanocrystals with strong single band NIR emission: simple click chemistry route to make water dispersible nanocrystals with various functional groups

2016 ◽  
Vol 40 (4) ◽  
pp. 3080-3085 ◽  
Author(s):  
Brahmaiah Meesaragandla ◽  
Debashrita Sarkar ◽  
Venkata N. K. B. Adusumalli ◽  
Venkataramanan Mahalingam
Keyword(s):  
Double Bond ◽  
Click Chemistry ◽  
Functional Groups ◽  
Single Band ◽  
Water Dispersible ◽  
Nir Emission

A simple thiol–ene click chemistry strategy to develop upconverting nanocrystals with different functional groups.

Cu(II)-Catalyzed [3+2] Annulation of Thioamides with AIBN: Facile Access to Highly Functionalized Thiazolidine-4-ones

Synthesis ◽  
2021 ◽  
Author(s):  
Pragya Pali ◽  
Dhananjay Yadav ◽  
Gaurav Shukla ◽  
Maya Shankar Singh
Keyword(s):  
Double Bond ◽  
Functional Groups ◽  
Dual Role ◽  
Direct Access ◽  
One Pot ◽  
Simple Method ◽  
Two Component ◽  
Thiazolidine Ring ◽  
Coupling Partner

An efficient and versatile copper-catalyzed unprecedented intermolecular radical [3 + 2] annulation of thioamides with azobisisobutyronitrile (AIBN) is described. This two-component one-pot copper(II)-catalyzed transformation has been achieved via cascade formation of C-S/C−N bonds through the cyclization of in situ generated N,S-acetal intermediate from β-ketothioamide. This operationally simple method allows direct access to synthetically demanding thiazolidin-4-ones in good to excellent yields containing diverse functional groups of different electronic and steric nature. Remarkably, the readily available reaction partners, avoidance of expensive/toxic reagents and the gram scale synthesis are additional attributes to this strategy. AIBN here plays a dual role as radical initiator and unusual source of two carbon coupling partner. Notably, the products possess Z-stereochemistry with regard to the exocyclic C=C double bond at the 2-position of the thiazolidine ring.

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