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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.


Substrates scope of ‘transition-metal-free’ IDC using KOt-Bu/I2. Reproduced from [46].
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Figure 3: Substrates scope of ‘transition-metal-free’ IDC using KOt-Bu/I2. Reproduced from [46].

Mentions: Next, we focussed our attention to prenylated, reverse-prenylated, and geranylated hexahydropyrrolo[2,3-b]indole alkaloids showing broad biological activities [55–61]. For the synthesis of these compounds, we thought of utilizing the Pd-catalyzed decarboxylative strategy to install the prenyl, reverse-prenyl, or geranyl group at the 3-position of 2-oxindole starting from the corresponding β-amido esters such as 8 [47]. This further extended the methodology to a variety of β-N-arylamido esters containing allyl, methallyl, dimethylallyl, and geranyl ester groups (9). It is noteworthy that, the substrate of type 9 could undergo smooth IDC in the presence of iodine (conditions A) to provide an access to compounds 8 in synthetically useful yields (Fig. 3).


Synthesis of 2-oxindoles via 'transition-metal-free' intramolecular dehydrogenative coupling (IDC) of sp 2 C – H and sp 3 C – H bonds
Substrates scope of ‘transition-metal-free’ IDC using KOt-Bu/I2. Reproduced from [46].
© Copyright Policy - Beilstein
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4979638&req=5

Figure 3: Substrates scope of ‘transition-metal-free’ IDC using KOt-Bu/I2. Reproduced from [46].
Mentions: Next, we focussed our attention to prenylated, reverse-prenylated, and geranylated hexahydropyrrolo[2,3-b]indole alkaloids showing broad biological activities [55–61]. For the synthesis of these compounds, we thought of utilizing the Pd-catalyzed decarboxylative strategy to install the prenyl, reverse-prenyl, or geranyl group at the 3-position of 2-oxindole starting from the corresponding β-amido esters such as 8 [47]. This further extended the methodology to a variety of β-N-arylamido esters containing allyl, methallyl, dimethylallyl, and geranyl ester groups (9). It is noteworthy that, the substrate of type 9 could undergo smooth IDC in the presence of iodine (conditions A) to provide an access to compounds 8 in synthetically useful yields (Fig. 3).

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.