Stereochemistry and mechanism of the Brønsted acid catalyzed intramolecular hydrofunctionalization of an unactivated cyclic alkene.

Published

Journal Article

Through employment of deuterium-labeled substrates, the triflic acid catalyzed intramolecular exo addition of the X-H(D) (X=N, O) bond of a sulfonamide, alcohol, or carboxylic acid across the C=C bond of a pendant cyclohexene moiety was found to occur, in each case, with exclusive formation (≥90%) of the anti-addition product without loss or scrambling of deuterium as determined by (1)H and (2)H NMR spectroscopy and mass spectrometry analysis. Kinetic analysis of the triflic-acid-catalyzed intramolecular hydroamination of N-(2-cyclohex-2'-enyl-2,2-diphenylethyl)-p-toluenesulfonamide (1a) established the second-order rate law: rate=k(2)[HOTf][1a] and the activation parameters ΔH(++)=(9.7±0.5) kcal mol(-1) and ΔS(++)=(-35±5) cal K(-1) mol(-1). An inverse α-secondary kinetic isotope effect of k(D)/k(H) =(1.15±0.03) was observed upon deuteration of the C2' position of 1a, consistent with partial C-N bond formation in the highest energy transition state of catalytic hydroamination. The results of these studies were consistent with a mechanism for the intramolecular hydroamination of 1a involving concerted, intermolecular proton transfer from an N-protonated sulfonamide to the alkenyl C3' position of 1a coupled with intramolecular anti addition of the pendant sulfonamide nitrogen atom to the alkenyl C2' position.

Full Text

Duke Authors

Cited Authors

  • Brooner, REM; Widenhoefer, RA

Published Date

  • May 2011

Published In

Volume / Issue

  • 17 / 22

Start / End Page

  • 6170 - 6178

PubMed ID

  • 21506179

Pubmed Central ID

  • 21506179

Electronic International Standard Serial Number (EISSN)

  • 1521-3765

International Standard Serial Number (ISSN)

  • 0947-6539

Digital Object Identifier (DOI)

  • 10.1002/chem.201003128

Language

  • eng