Divergent Reactivity of δ- and β'-Acetoxy Allenoates with 2-Sulfonamidoindoles via Phosphine Catalysis: Entry to Dihydro-α-carboline, α-Carboline, and Spiro-cyclopentene Motifs

The reactivity of 2-sulfonamidoindoles with acetoxy allenoates under phosphine catalysis depends on the disposition of the acetoxy (OAc) group on the allenoate. In the temperature-controlled [3 + 3] annulations, d-acetoxy allenoates afforded dihydrocarboline and carboline scaffolds with carbon-nitro...

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Bibliographic Details
Published in:Journal of organic chemistry Vol. 86; no. 17; pp. 11583 - 11598
Main Authors: Debnath, Shubham, Kumar, A. Sanjeeva, Chauhan, Sachin, Swamy, K. C. Kumara
Format: Journal Article
Language:English
Published: WASHINGTON Amer Chemical Soc 03.09.2021
Subjects:
Chemistry
Chemistry, Organic
Physical Sciences
Science & Technology
MIGRATION
CYCLOADDITION REACTIONS
ADDITION/CYCLOADDITION
ENANTIOSELECTIVE SYNTHESIS
ASYMMETRIC 3+2 ANNULATIONS
BENZOFURANS
ALLENES
CYCLIZATION
ACCESS
INDOLES
ISSN:0022-3263, 1520-6904, 1520-6904
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Summary:The reactivity of 2-sulfonamidoindoles with acetoxy allenoates under phosphine catalysis depends on the disposition of the acetoxy (OAc) group on the allenoate. In the temperature-controlled [3 + 3] annulations, d-acetoxy allenoates afforded dihydrocarboline and carboline scaffolds with carbon-nitrogen nucleophilic 2-sulfonamidoindoles, in which allenoate serves as a beta-, gamma-, and delta-carbon donor. At room temperature (25 degrees C), dihydro-alpha-carboline motifs were obtained exclusively through Michael addition, 1,4-proton shift, isomerization, 1,2-proton transfer, phosphine elimination, and aza-Michael addition. The higher temperature (80 degrees C) cascade protocol using Ph3P-Cs2CO3 combination involves addition-elimination, aza-Claisen rearrangement, tosyl migration, and aromatization as key steps to give alpha-carbolines containing tosyl functionality at the gamma-carbon. In contrast, with beta'-acetoxy allenoate, 2-sulfonamidoindole acts only as a carbo-nucleophile in (p-tolyl)(3)P-directed [4 + 1] spiro-annulation, leading to five-membered spiro-carbocyclic motifs essentially as single diastereomers (dr >20:1) via chemoselective carbo-annulation.
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ISSN:0022-3263
1520-6904
1520-6904
DOI:10.1021/acs.joc.1c01137