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Synthesis of 2-oxindoles via 'transition-metal-free' intramolecular dehydrogenative coupling (IDC) of sp 2 C – H and sp 3 C – H bonds

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ABSTRACT

The synthesis of a variety of 2-oxindoles bearing an all-carbon quaternary center at the pseudo benzylic position has been achieved via a ‘transition-metal-free’ intramolecular dehydrogenative coupling (IDC). The construction of 2-oxindole moieties was carried out through formation of carbon–carbon bonds using KOt-Bu-catalyzed one pot C-alkylation of β-N-arylamido esters with alkyl halides followed by a dehydrogenative coupling. Experimental evidences indicated toward a radical-mediated path for this reaction.

No MeSH data available.


Intramolecular-dehydrogenative-coupling (IDC) of 3a and 5a. Reproduced from [46].
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C7: Intramolecular-dehydrogenative-coupling (IDC) of 3a and 5a. Reproduced from [46].

Mentions: Kündig et al. in their oxidative coupling process using 2.2 equivalent of CuCl2 showed that it is important to have a tertiary carbon α- to the amide for the process to be radical mediated [38–39]. Also, it is well evident from literature that the oxidation processes using Mn(OAc)3 as oxidant follow a radical pathway [82–86]. In fact, the reaction of 3a also afforded 2-oxindole 4a in 69% yield when the oxidative coupling was carried out in presence of 1.2 equiv of Mn(OAc)3 (Scheme 7). A similar result was also observed when reaction was carried out using C-methyl β-N-arylamido ester 5a (Scheme 7) [82–86].


Synthesis of 2-oxindoles via 'transition-metal-free' intramolecular dehydrogenative coupling (IDC) of sp 2 C – H and sp 3 C – H bonds
Intramolecular-dehydrogenative-coupling (IDC) of 3a and 5a. Reproduced from [46].
© Copyright Policy - Beilstein
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4979638&req=5

C7: Intramolecular-dehydrogenative-coupling (IDC) of 3a and 5a. Reproduced from [46].
Mentions: Kündig et al. in their oxidative coupling process using 2.2 equivalent of CuCl2 showed that it is important to have a tertiary carbon α- to the amide for the process to be radical mediated [38–39]. Also, it is well evident from literature that the oxidation processes using Mn(OAc)3 as oxidant follow a radical pathway [82–86]. In fact, the reaction of 3a also afforded 2-oxindole 4a in 69% yield when the oxidative coupling was carried out in presence of 1.2 equiv of Mn(OAc)3 (Scheme 7). A similar result was also observed when reaction was carried out using C-methyl β-N-arylamido ester 5a (Scheme 7) [82–86].

View Article: PubMed Central - HTML - PubMed

ABSTRACT

The synthesis of a variety of 2-oxindoles bearing an all-carbon quaternary center at the pseudo benzylic position has been achieved via a ‘transition-metal-free’ intramolecular dehydrogenative coupling (IDC). The construction of 2-oxindole moieties was carried out through formation of carbon–carbon bonds using KOt-Bu-catalyzed one pot C-alkylation of β-N-arylamido esters with alkyl halides followed by a dehydrogenative coupling. Experimental evidences indicated toward a radical-mediated path for this reaction.

No MeSH data available.