Abstract
The synthesis of N,N′-diaryl-1,3-benzene-dicarbothioamides was accomplished in only two steps with good yields, and their ability to act as hydrogen-bond donors in Diels–Alder reactions was evaluated. These new organocatalysts were indeed able to promote the cycloaddition of cyclopentadiene to α,β-unsaturated aldehydes. In the attempt to control the absolute stereochemistry of the reaction, chiral catalysts were also prepared by simple condensation of isophthalic acid and α-amino acid derivatives. Molecular mechanics calculations were performed to elucidate the mode of action of these metal-free catalytic systems and to find a rationale for the achieved enantioselectivity.
ACKNOWLEDGMENTS
This work was supported by Ministero Istruzione, Università e Ricerca (MIUR) (Rome) within the national project “Nuovi metodi catalitici stereoselettivi e sintesi stereoselettiva di molecole funzionali.”
Notes
a Determined by 1H NMR and confirmed after chromatographic purification after 72 h at 25°C.
b Determined by 1H NMR and confirmed by HPLC analysis.
a Determined by 1H NMR and confirmed after chromatographic purification after 72 h without any solvent.
b Determined by 1H NMR.
c Determined by GC on chiral stationary phase (Agilent HP-chiral) t major exo = 59.1 min, t min exo = 59.6 min, t major endo = 60.6 min, t min endo = 62.2 min.