Metal-Free [2 + 2]-Photocycloaddition of (Z)-4-Aryliden-5(4H)-Oxazolones as Straightforward Synthesis of 1,3-Diaminotruxillic Acid Precursors: Synthetic Scope and Mechanistic Studies

  1. García-Montero, A. 3
  2. Rodriguez, A.M. 4
  3. Juan, A. 4
  4. Velders, A.H. 45
  5. Denisi, A. 3
  6. Jiménez-Osés, G. 1
  7. Gómez-Bengoa, E. 2
  8. Cativiela, C. 3
  9. Gómez, M.V. 4
  10. Urriolabeitia, E.P. 3
  1. 1 Universidad de La Rioja
    info

    Universidad de La Rioja

    Logroño, España

    ROR https://ror.org/0553yr311

  2. 2 Universidad del País Vasco/Euskal Herriko Unibertsitatea
    info

    Universidad del País Vasco/Euskal Herriko Unibertsitatea

    Lejona, España

    ROR https://ror.org/000xsnr85

  3. 3 Universidad de Zaragoza
    info

    Universidad de Zaragoza

    Zaragoza, España

    ROR https://ror.org/012a91z28

  4. 4 Universidad de Castilla-La Mancha
    info

    Universidad de Castilla-La Mancha

    Ciudad Real, España

    ROR https://ror.org/05r78ng12

  5. 5 Laboratory of BioNanoTechnology, Wageningen University, Bornse Weilanden 9, Wageningen, Netherlands
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Revista:
ACS Sustainable Chemistry and Engineering

ISSN: 2168-0485

Año de publicación: 2017

Volumen: 5

Número: 9

Páginas: 8370-8381

Tipo: Artículo

DOI: 10.1021/ACSSUSCHEMENG.7B02140 SCOPUS: 2-s2.0-85028920511 WoS: WOS:000410006200102 GOOGLE SCHOLAR

Otras publicaciones en: ACS Sustainable Chemistry and Engineering

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Resumen

The direct [2 + 2]-photocycloaddition of (Z)-2-phenyl-4-aryliden-5(4H)-oxazolones 1 to give 1,3-diaminotruxillic cyclobutane derivatives 2 in very good yields (75-100%) is reported. The reaction takes place by irradiation of CH2Cl2 solutions of 1 with blue light (465 nm) provided by light-emitting diode (LED) lamps of low power (around 1 W) for 72 h. Four isomers of the 1,3-diaminotruxillic cyclobutanes 2 were obtained; all of them fully characterized by a combination of nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction analysis. The reaction shows a certain selectivity, since one of the isomers (the epsilon) is obtained preferentially, and works for electron-releasing and electron-withdrawing substituents at the arylidene ring. A novel setup is presented for the in-line monitoring of the continuous flow photoassisted synthesis of the cyclobutane derivatives 2 by NMR spectroscopy, with the microreactor dramatically reducing reaction times to only 30 min with clear product distribution of up to four isomers. The mechanism of this [2 + 2]-photocycloaddition has been calculated by density functional theory (DFT) methods, explaining all experimental findings. The reaction takes place through a stepwise formation of two new C-C bonds through a transient diradical singlet intermediate. The isomeric distribution of the final products is not due to equilibration processes but instead reflects the kinetic preference during the rate limiting C-C bond formation step. © 2017 American Chemical Society.